Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Older adults, mealtime-related emotions, and functionalities : tailoring protein-enriched meals
    Uijl, Louise C. den - \ 2016
    Wageningen University. Promotor(en): Kees de Graaf, co-promotor(en): Stefanie Kremer; Gerry Jager. - Wageningen : Wageningen University - ISBN 9789462578920 - 178
    meals - emotions - elderly nutrition - elderly - smell - food preferences - protein - proteins - questionnaires - young adults - chocolate - maaltijden - emoties - ouderenvoeding - ouderen - reuk - voedselvoorkeuren - eiwit - eiwitten - vragenlijsten - jongvolwassenen - chocolade

    Background and aim

    Dietary proteins are of special interest for the heterogeneous group of older adults, since these people do not always have an adequate protein intake. When protein-rich products are better aligned with the requirements of older persons, an adequate nutrient intake is more likely. In this thesis we therefore explored two approaches for tailoring protein-enriched meals to older consumer subgroups; emotion-based and functionality-based. We expected a better ‘product-cluster fit’ (i.e. a more positive meal experience) when the clusters’ meal associations are congruent to their mealtime expectations.


    We conducted an online survey in which vital community-dwelling older adults (n=392) reported their mealtime-related emotions and mealtime functionality. Using a hierarchical clustering analysis we described clusters within our population. Subsequently, we explored the extent to which the expectations of these clusters can be applied for the development of tailored protein-enriched meals. For the emotion-based approach, we conducted two central location tests (CLTs, n=461) to explore older adults’ food-evoked emotions. For the functionality-based approach we conducted in-depth interviews in order to get further insights regarding functional mealtime expectations and attitudes towards proteins and protein-enrichment. Based on the latter insights we tailored PE meal concepts to two functionality-based segments. In a final home-use test, the members of the functionality-based segments (n=91) prepared and evaluated the tailored PE meal concepts.


    The emotion-based approach resulted in four clusters; pleasurable averages, adventurous arousals, convivial indulgers, and indifferent restrictives. These emotions that these segments associated with their mealtimes varied along the two dimensions valence and arousal. However, from both CLTs we learned that the variation in valence-arousal as observed for mealtime-related emotions was not observed for emotions related to actual foods. The latter makes it challenging to identify products that evoke emotions congruent to the mealtime expectations of the emotion-based clusters.

    With regard to the functionality-based approach, we encountered three clusters; physical nutritioners, cosy socialisers, and thoughtless averages. The cosy socialisers value the social interactions and cosiness during their mealtimes, whereas the physical nutritioners focus more on the health and nutrient aspects of meals. Thoughtless averages have the least distinctive mealtime expectations. We translated these functional mealtime expectations into two PE meal concepts; one tailored to cosy socialisers and one tailored to physical nutritioners. These meal concepts were well-accepted by the participants. However, congruency between mealtime expectations and functional meal associations did not result in a better ‘product-cluster fit’.


    Given the challenge to identify congruency between the meal associations and the mealtime expectations of the emotion-based clusters, we consider the emotion-based approach to be not yet actionable enough as a basis for tailoring PE products to older consumers. In contrast, the functionality-based approach appeared to be more promising, since the functional meal expectations could be translated to well-accepted tailored PE meal concepts. However, the effectivity of our functionality-based approach was not yet confirmed in this thesis, since congruency between functional meal associations and functional meal expectations did not necessarily result in a better ‘product-cluster fit’. Future studies, focussing on e.g. other meal types, are recommended to further explore mealtime functionality as a basis for tailoring PE meals to older consumer subgroups.

    Vertrouwde geur geeft minder stress bij spenen
    Rotgers, G. ; Oostindjer, M. ; Bolhuis, J.E. - \ 2011
    V-focus 8 (2011)6. - ISSN 1574-1575 - p. 36 - 37.
    varkenshouderij - biggen - reuk - geurstoffen - diergedrag - stressfysiologie - dierenwelzijn - pig farming - piglets - smell - odours - animal behaviour - stress physiology - animal welfare
    Varkens hechten zeer aan geur: de aroma’s die de ongeboren biggen al in de baarmoeder ‘opsnuiven’, hebben lange tijd een gunstig e…ffect op het dier. Bijvoorbeeld na het spenen. Biggen die dan de vertrouwde aroma’s kunnen ruiken, hebben daardoor minder stress. Dit blijkt uit onderzoek van Marije Oostindjer en Liesbeth Bolhuis, onderzoekers van de Leerstoelgroep Adaptatiefysiologie van Wageningen UR.
    Unravelling the malaria mosquito's sense of smell: neural and behavioural responses to human-derived compounds
    Suer, R.A. - \ 2011
    Wageningen University. Promotor(en): Willem Takken; Marcel Dicke, co-promotor(en): Joop van Loon. - S.l. : s.n. - ISBN 9789085858584 - 204
    anopheles gambiae - reuk - geurstoffen - mens - neurofysiologie - receptoren - diergedrag - anopheles gambiae - smell - odours - man - neurophysiology - receptors - animal behaviour
    Tailor-made memory: natural differences in associative olfactory learning in two closely related wasp species
    Berg, M. van den - \ 2009
    Wageningen University. Promotor(en): Marcel Dicke; Louise Vet, co-promotor(en): Hans Smid. - [S.l. : S.n. - ISBN 9789085853725 - 171
    cotesia glomerata - cotesia rubecula - vespidae - insectenplagen - pieris brassicae - pieris rapae - reuk - leren - geheugen - africhten van dieren - genexpressie - aminozuursequenties - modellen - sluipwespen - multitrofe interacties - cotesia glomerata - cotesia rubecula - vespidae - insect pests - pieris brassicae - pieris rapae - smell - learning - memory - training of animals - gene expression - amino acid sequences - models - parasitoid wasps - multitrophic interactions
    Learning and memory formation are often seen as traits that are purely beneficial, but they are associated with metabolic costs as well. Since costs and gains of learning and memory are expected to vary between species, the ease and speed with which stable (consolidated) long-term memory (LTM) is formed, is expected to differ between species. For animals that occupy different ecological niches, ‘slow’ learning may be as adaptive as ‘fast’ learning. If an animal encounters a relatively predictable environment during its lifetime, fast learning is a good strategy. If the environment is relatively unpredictable, however, an animal may need more time and experiences to evaluate information before storing it as long-lasting memories. This concept is known as tailor-made memories: a species learns in the way that is most favourable, given the circumstances. In order to assess how such tailor-made memories evolve, I have used a multitrophic model system. This system consisted of (1) two closely related parasitic wasps (Cotesia glomerata and C. rubecula) that show a profound difference in learning, (2) the herbivorous cabbage white butterfly larvae Pieris brassicae and P. rapae, in which the parasitic wasps lay their eggs, and (3) the host plants Brussels sprouts (Brassica oleracea var. Gemmifera) and nasturtium (Tropaeolum majus).

    In my experiments, the wasps could learn to associate the odours of a plant with the presence of suitable hosts, by having one or more oviposition experiences (‘conditioning trials’) on that plant. Previous experiments showed that C. glomerata needs only one conditioning trial to form LTM, whereas C. rubecula needs three trials spaced in time to do so. In addition to LTM, another form of consolidated memory exists; anaesthesia-resistant memory (ARM). Both LTM and ARM are resistant to retrograde amnesia, which can be induced by cooling the wasps after conditioning. In contrast to LTM however, ARM is not protein synthesis-dependent. It can therefore be seen as a ‘cheap’ form of long lasting memory. Consolidated memory in C. glomerata is thought to consist exclusively of LTM, whereas in C. rubecula it appears to be a mixture of both ARM and LTM.

    LTM formation requires protein synthesis, a process in which the transcription factor cAMP response element-binding protein (CREB) plays a key role. As a result of alternative splicing of the CREB mRNA transcript, the CREB protein occurs in different forms called isoforms. In model organisms such as the fruit fly Drosophila melanogaster, the mollusc Aplysia californica, and also in mammals such as mice and men, CREB isoforms have been shown to activate or repress transcription. Therefore, it has been hypothesized that the ratio of activator and repressor isoforms acts as a molecular switch for LTM formation. Such a switch could be responsible for species-specific differences in learning and memory.

    In this study the CREB gene of C. glomerata and C. rubecula was cloned and sequenced, and nine isoforms were identified in the two Cotesia species. The abundance of two of the nine mRNA variants coding for these isoforms differs significantly between C. glomerata and C. rubecula; the other variants are expressed similarly in both species. A conditioning trial, however, seems to induce changes in the expression of some of the major isoforms, indicating that the learning process itself may establish a ratio between activators and repressors that determines whether LTM is consolidated or not.

    Although such molecular mechanisms can potentially act very quickly, it may sometimes take up to days or weeks before information is stored in long-lasting memories. To explain how and why such differences in memory dynamics occur, we need insight in what happens when selection acts on natural variation in learning rate. In order to investigate this, I applied a bidirectional selection regime and reared two lines of C. glomerata wasps that differed significantly in learning rate (the decreased-learning line (DLL) and the increased-learning line (ILL)).

    By applying the protein synthesis inhibitor anisomycin before conditioning and measuring memory retention after conditioning, I showed that the memory consolidation dynamics of the selection lines differed. The DLL did not consolidate LTM anymore, whereas the ILL still did. By combining this study with experiments in which I induced retrograde amnesia by cooling at certain time intervals after conditioning, I demonstrated that in C. glomerata, anaesthesia-sensitive short-term memory directly consolidates into LTM, without an intermediate ARM phase. ARM represents a low-cost form of long-lasting memory (since it is not protein synthesis-dependent) and its presence is assumed to be favourable in animals that need more time to evaluate information, before storing it in the form of consolidated memories (e.g., in C. rubecula). The inability of C. glomerata to form ARM is costly because it may lead to an expenditure of energy (i.e., protein synthesis) on the ‘premature’ storage of unreliable information.

    Comparison of my selection lines showed that a high learning rate has costs. Longevity appeared to be significantly higher in wasps from the DLL than in those from the ILL. Moreover, females of the ILL have significantly larger brains than females from the DLL, while retaining a similar body size. These exciting results show that trade-offs occur (i.e., brain size vs. longevity) as a result of the bidirectional selection pressure that we applied. Moreover, the costs associated with a high learning rate seem to be of a constitutive nature. This means that animals that are able to quickly form consolidated memory pay for it by maintaining a large, costly brain and having a decreased lifespan, even when they do not actually use their learning abilities.

    The results of my work show that comparative research involving a model system consisting of two closely related animals with a natural difference in learning rate yields unique information, and is preferred over the use of ‘traditional’ model organisms. It enables testing of various hypotheses with an ecologically relevant learning paradigm. Neuroscience (and biology in general) would benefit greatly from an increase in the use of model systems that consist of closely related species that show differences in the trait of interest. The work described in this thesis shows how fruitful such a comparative approach can be.
    Geurend sortiment verkoopt : maak de juiste keuze
    Hoffman, M.H.A. - \ 2007
    De Boomkwekerij 2007 (2007)14. - ISSN 0923-2443 - p. 10 - 11.
    plantenkwekerijen - sierplanten - overblijvende planten - welriekendheid - aroma - reuk - cultivars - rassen (planten) - nurseries - ornamental plants - perennials - fragrance - aroma - smell - cultivars - varieties
    De laatste jaren komt er meer erkenning voor de eigenschap 'geur' in sierplanten, die eigenschap is jarenlang miskend en verwaarloosd bij het selecteren van nieuwe cultivars. Planten die lekker ruiken hebben zonder twijfel een streepje voor op planten die niet geuren. Steeds vaker komen geuraanduidingen in catalogi en labels te staan. Met lijst van Top 10 geurende gewassen
    Sensory and behavioural responses of the malaria mosquito Anopheles gambiae to human odours
    Qiu, Y.T. - \ 2005
    Wageningen University. Promotor(en): Joop van Lenteren, co-promotor(en): Joop van Loon; Willem Takken. - [S.l.] : S.n. - ISBN 9789085042921 - 210
    anopheles gambiae - culicidae - diergedrag - geurstoffen - reuk - mens - malaria - lokstoffen - gedrag bij zoeken van een gastheer - anopheles gambiae - culicidae - animal behaviour - odours - smell - man - malaria - attractants - host-seeking behaviour
    Malaria is one of the most serious human diseases, affecting between 300 and 600 million people per year and killing, on average, two children per minute. In tropicalAfricathe mosquito Anopheles gambiae Giles sensu stricto is responsible for much of the transmission of malaria parasites between humans. This mosquito species preferably feeds on human blood, rests inside human houses and breeds close to human dwellings, making it an effective malaria vector. The major cues guiding Anopheles gambiae females to their human hosts are volatiles emanating from the human body. The main aim of the present thesis was to investigate the chemical components in human emanations that play a role in the host-seeking behaviour of this mosquito species and how these human odours are perceived by the olfactory system of the mosquito. The knowledge obtained can be applied in developing odour-baited traps that can be used to protect humans from being bitten by mosquitoes or to decrease the chance of being bitten by mosquitoes and to provide an alternative for the traditional but questionable "human landing" method in the investigation of mosquito population size.

    Glass beads to which skin emanations from human hands had been transferred elicited a level of attraction similar to a human hand ( Chapter 2 ). The attractiveness of these handled glass beads faded away four hours after transfer onto the beads. The headspace of handled glass beads elicited a dose-dependent EAG response. Glass beads provided a suitable neutral substrate for the transfer of human odour to enable the investigation of behavioural and electrophysiological activities of An. gambiae exposed to these odours and to allow chemical analysis of the human skin emanations by gas-chromatography-mass spectrometry performed in a twin-project.

    To study the chemical basis for the inter-individual differences in human attractiveness to mosquitoes , emanations from 27 human individuals, collected on glass beads, were tested against ammonia in a dual-choice olfactometer to establish the degree of attractiveness to An. gambiae ( Chapter 3 ). There were clear differences in the trap entry response as well as in the attractiveness relative to that of ammonia between the skin emanations of different volunteers. Consistency of the differences was observed when emanations of the three most and the three least attractive volunteers were tested pair-wise. Emanations from males elicited a higher trap entry response than those from females. Odours of younger volunteers significantly raised the trap entry response and were preferred over odours from older volunteers. Electroantennogram responses to skin emanations from volunteers with different behavioural attractiveness were not in all cases positively related to the behavioural response level, suggesting the involvement of repellent components.

    Stockings worn by humans were previously shown to be highly attractive to females of An. gambiae . The headspace of nylon stockings was collected and analysed with gas chromatography coupled on-line to electroantennography (EAG). EAG responses were detected consistently at 23 retention times, and 14 compounds that elicited such EAG responses were tentatively identified. These compounds, however, were not of typically human origin ( Chapter 4 ).

    Ammonia, L-lactic acid and a mixture of carboxylic acids were previously found attractive to An. gambiae. These compounds are all present in human skin odours, therefore a mixture of these components was studied in a dual-choice olfactometer ( Chapter 5 ). Ammonia was an attractant on itself, whereas lactic acid alone was not attractive. Carboxylic acids, offered as a mixture of 12 compounds, were repellent at the concentration tested. The addition of ammonia to the carboxylic acid mixture overruled the repellent effect of the latter. Combining ammonia with either lactic acid or the carboxylic acid mixture did not enhance the attractiveness of ammonia alone. However, a synergistic effect was found when ammonia, lactic acid and the carboxylic acids were applied as a blend.

    Human odour compounds that elicited electrophysiological or behavioural responses were tested in combination with ammonia + L-lactic acid against ammonia alone ( Chapter 6 ). The results showed that C3-C8 and C14 carboxylic acids augmented the attractiveness of ammonia + lactic acid at certain concentrations, whereas alcoholsketones4-ethylphenol and indole only reduced the attractiveness at the concentrations tested. For some compounds, no effect was found at any of the concentrations tested.

    Based on the behavioural and electrophysiological findings, a field study in The Gambia (West Africa) was carried out to investigate the efficiency of mosquito traps baited with synthetic odour blends or human odour ( Chapter 7 ). This study showed that odours released from counterflow geometry (CFG) traps baited with up to nine compounds that were mixed during release were in many cases more attractive than odours from a tent occupied by a human. Carbon dioxide substantially increased the catch of the CFG traps for all mosquito species. CFG traps baited with the mixture of ammonia + lactic acid + 3-methyl butanoic acid + CO 2 resulted in the highest catches for most mosquito groups; the mixture is considered to be a promising candidate odour blend in the control of nuisance mosquitoes. Experiments with traps indoors showed that one odour mixture, consisting of ammonia + lactic acid + CO 2 + geranyl acetone + indole + 4-ethyl phenol was more attractive for An. gambiae than the control odour; this mixture holds promise for further experiments under conditions of higher An. gambiae abundance and for implementation in vector control programs.

    Using a single sensillum recording method, an electrophysiological study on the olfactory neuron responses of female An. gambiae mosquitoes was undertaken ( Chapter 8 ). Six functional types of sensilla trichodea and five functional types of sensilla basiconica (grooved peg sensilla) were identified. "Generalist" ORNs that are tuned to a broad range of odours were found in sensilla trichodea subtype E, whereas "moderate specialist" ORNs that are tuned to a narrow range of odours were found in subtype C and grooved peg sensilla, with two "extreme specialist" ORNs tuned to only one odour. There was overlap in response spectra between sensilla trichodea E and C or grooved peg sensilla, but no overlap was found between sensilla trichodea C and grooved peg sensilla except that both responded to ammonia. Neurons associated with the same sensillum tended to respond to similar odour stimuli but with different sensitivities. Neurons in grooved peg sensilla were tuned to more polar compounds including the important behavioural attractant ammonia and its synergist lactic acid, responses to which were only found in grooved peg sensilla. Phenols were among the most effective stimulants for several neuron types belonging to different functional classes. Across-fibre patterning is the most plausible coding principle operating in the olfactory system of this mosquito species.

    After a blood meal, female mosquitoes minimise host seeking activity and rest during egg maturation. To investigate whether the sensitivity of olfactory neurons changed after a blood meal and whether these changes correlate with the observed behavioural change, we compared the responses of ORNs in sensilla trichodea and grooved peg sensilla 2 - 24 h post blood meal with that of mosquitoes that had not fed on blood ( Chapter 9 ). Three instead of two functional types of sensilla trichodea E were found following a blood meal. A functional type that had not been detected in mosquitoes deprived of blood was found repeatedly. The most responsive neuron of the "new" functional type of sensillum showed a high sensitivity to indole. This neuron was also highly responsive to C6-9 carboxylic acids and moderately responsive to the human-specific odour compounds 7-octenoic acid and 3-methyl-2-hexenoic acid. These results indicate that changes in sensitivity and response profile of ORNs as a result of a blood meal are involved in modulating behaviour of An. gambiae females.

    The main conclusions from this thesis can be summarised as follows. This thesis provides additional evidence that chemical cues play a substantial role in the host attraction of An. gambiae (Chapter 2) and that skin emanations alone contribute significantly to inter-individual differences in attractiveness of humans to mosquitoes (Chapter3). The GC-EAG method can be used in the detection of kairomones used by An. gambiae , but a suitable substrate for collecting odours is essential (Chapter 4). Synergism was demonstrated to operate between ammonia, lactic acid and a mixture of carboxylic acids in attracting females of An. gambiae (Chapter 5) and olfactometric studies demonstrated the dose-dependent effects of human odour components to An. gambiae in addition to ammonia and lactic acid (Chapter 6). The results of our field study provided evidence that mosquito traps baited with synthetic mixtures were superior to those baited with a human being, suggesting great potential of these traps in future malaria control programs (Chapter 7). Based on the response to several compounds, olfactory receptor neurones were classified into functional groups, providing fundamental information for future studies of these neurons (Chapter 8). Qualitative and quantitative changes were found in olfactory neuron responsiveness before and after a blood meal, suggesting the involvement of the peripheral nervous system in the modulation of mosquito behaviour observed in different physiological stages (Chapter 9).

    Associative learning in two closely related parasitoid wasps: a neuroecological approach
    Bleeker, M.A.K. - \ 2005
    Wageningen University. Promotor(en): Louise Vet, co-promotor(en): Hans Smid; Joop van Loon. - [S.l.] : S.n. - ISBN 9789085043201 - 135
    nuttige insecten - cotesia glomerata - cotesia rubecula - leervermogen - geurstoffen - reuk - neurofysiologie - vespidae - neurobiologie - beneficial insects - cotesia glomerata - cotesia rubecula - learning ability - odours - smell - neurophysiology - vespidae - neurobiology
    Insects are useful model organisms to study learning and memory. Their brains are less complex than vertebrate brains, but the basic mechanisms of learning and memory are similar in both taxa. In this thesis I study learning and subsequent memory formation in two parasitoid wasp species that differ in associative learning of the odours of plants on which they have encountered a host caterpillar. After ovipositing in a caterpillar on a certain plant species C. glomerata shifts its preference to the experienced plant odour, whereas C. rubecula does not shift plant odour preference after a similar experience. This difference in learning between these two closely related wasp species provides an attractive model to study physiological and ecological factors that could influence learning.

    As a first step to analyse possible physiological differences that could influence learning, I describe morphological, anatomical and histochemical aspects of the neural pathways that mediate associative learning of odours in these wasps. The two wasp species display a high degree of similarity in morphology of the olfactory pathway at both the level of the sensilla, and the level of the glomeruli, the primary olfactory neuropile. I furthermore identify the octopaminergic neurons that could mediate the reward stimulus in the two wasp species, but the results did not allow us to distinguish possible dissimilarities between the species.

    In addition I redefined the difference in preference learning between the two species in terms of associative and non-associative learning and analysed the temporal dynamics of the memory trace. Both wasps display associative learning after an oviposition reward conditioning, but the temporal dynamics differ. C. glomerata displays a stable memory for the experienced odour that lasts for at least five days, whereas in C. rubecula the memory starts to wane after one day.

    Finally, I studied the effect of physiological and ecological traits of hosts as possible factors influencing memory formation. For this I used two geographically disjunct populations of C. glomerata that differ in their host use. Both populations only change preference after an oviposition reward on their preferred host species, suggesting that physiological factors exert a major influence on learning in these two populations. I discuss the ultimate factors that could have contributed to a difference in learning in C. glomerata and C. rubecula
    Fatal attraction. Control of the housefly (Musca domestica)
    Smallegange, R.C. - \ 2004
    Entomologische Berichten 63 (2004). - ISSN 0013-8827 - p. 87 - 92.
    musca domestica - plagenbestrijding - diergedrag - fototaxis - reuk - musca domestica - pest control - animal behaviour - phototaxis - smell
    Despite its long association with man, the housefly (Musea domestica Linnaeus) remains one of the most difficult pests to control. It is a ubiquitous insect that can be found in houses, stables, food processing factories and other domesticated areas and buildings. Reliance on insecticides for fly control is decreasing because of increased environmental constraints and insecticide resistance. So far, biological control with natural enemies often has disappointing results. Light- and odour-baited traps are considered to be promising devices to control houseflies indoors, although they are not yet effective enough to reduce fly populations to acceptable levels. Therefore, possibilities to improve the effectiveness of these types of traps were examined
    Taste perception with age
    Mojet, J. - \ 2004
    Wageningen University. Promotor(en): J.H.A. Kroeze; Fons Voragen. - Wageningen : s.n. - ISBN 9789085040583 - 215
    smaakgevoeligheid - smaakdrempel - leeftijd - leeftijdsverschillen - reuk - taste sensitivity - taste threshold - age - age differences - smell
    Keywords: age, thresholds, supra-threshold intensities, pleasantness, optimally preferred concentration, olfactory deprivation,signal-to-noise ratio

    This thesis describes experiments studying age-related diferences in taste perception. Thresholds, supra-threshold intensities and pleasantness for ten different tastants, representing the five taste qualities sweet, sour, salty, bitter and umami were measured in the same group of elderly and young subjects. The tastants were dissolved in water and in product. Age has a deteriorating effect on taste sensitivity, which is already noticeable in the young-old group of elderly. First, this effect is generic in nature, i.e. more than 90% of the total variance attributable to age is due to age alone and less than 6% to age-related differences in the perception of the different taste qualities. Secondly, the differentiation between the different taste qualities is less distinct for elderly than for young people. A change in the signal-to-noise ratio at neural or perceptual level might be put forward to explain these phenomena. The outcome might support the hypothesis that the primary taste cortex is the locus of most accurate coding. Neither thresholds nor supra-threshold sensitivity were good predictors of the most preferred concentration of the tastants in product. Although the perceived intensities were lower for the elderly than for the young, the most preferred concentration of the tastants in product were similar for both age groups. It is suggested that the information about perception and affection might be processed in different regions of the brain. The most intriguing finding in this thesis is that smell seems to play a crucial role in taste perception. When the olfactory input is blocked, about 70% of the age differences in taste perception disappeared. Since taste and smell are so intimately related and accompanied by other sensations, such as mouthfeel, temperature and spiciness, it might not be a bad idea to investigate taste perception with a multimodal/multimethod approach, including all oral sensations in the investigation.

    Differential attractiveness of humans to the African malaria vector Anopheles gambiae Giles : effects of host characteristics and parasite infection
    Mukabana, W.R. - \ 2002
    Wageningen University. Promotor(en): J.C. van Lenteren; W. Takken; B.G.J. Knols. - S.l. : S.n. - ISBN 9789058087546 - 142
    anopheles gambiae - culicidae - gedrag bij zoeken van een gastheer - gastheerpreferenties - mens - reuk - gastheer parasiet relaties - plasmodium falciparum - malaria - anopheles gambiae - culicidae - host-seeking behaviour - host preferences - man - smell - host parasite relationships - plasmodium falciparum - malaria

    The results of a series of studies designed to understand the principal factors that determine the differential attractiveness of humans to the malaria vector Anopheles gambiae are described in this thesis. Specific attention was paid to the role of body emanations and infection (of humans) with the malaria parasite Plasmodium falciparum . The main findings of these studies are summarised in the following sections.

    Differential attractiveness of humans to Anopheles gambiae ( Chapter 1 )

    Although it has frequently been reported that human beings differ in their degree of attractiveness to mosquitoes, the principal causes that make certain individuals to be preferred more than others are not well known. This gap in knowledge has hindered the understanding of the transmission dynamics of malaria and other mosquito-borne diseases. From an epidemiological point of view, high malaria transmission rates are expected if mosquito vectors preferentially select infective humans for a blood meal, become infected, survive long enough for the parasites to develop to infective stages and proceed to bite uninfected individuals selectively. In terms of fitness, mosquito vectors would be better off if they select hosts that (1) are docile and less defensive so as to minimise feeding-associated risks of mortality, (2) have blood of a high nutritional value, (3) are free of (gametocyte) parasites, healthy and (4) have no anti-mosquito immunity. The answers to these epidemiological and fitness factors are still lacking. Furthermore, since host seeking is odour-mediated, the identification of chemical compounds responsible for attracting mosquitoes to their vertebrate hosts would help in developing traps that are useful for vector surveillance and control. Research in this area is rapidly advancing but has not produced tools for field application. It is felt that more research effort is needed so that new approaches towards understanding and combating disease vectors can be developed.

    Characterisation of mosquito blood meals using DNA markers (Chapters 2 & 3)

    The analysis of arthropod blood meals using molecular genetic markers was reviewed and forensic techniques borrowed from the Federal Bureau of Investigation (FBI), USA, used to evaluate the effect of blood meal size and extent of digestion on the ability to identify human DNA extracted from blood meals of Anopheles gambiae . The review recommended that proper and appropriate storage, determination of the concentration of host DNA and collection within few hours after ingestion are important parameters for improving the success of identifying blood meal sources of field-collected mosquitoes. Further, microsatellite markers were highlighted as being more appropriate than minisatellites in analysing blood meals that have been highly degraded e.g. through prolonged digestion. Also, mitochondrial DNA targets were recommended to be better than nuclear DNA targets for analysing blood meals that have been highly degraded. Blood meal size and (microsatellite) locus (analysed) were shown not to affect the success of amplifying human DNA extracted from blood meals of An. gambiae after having been digested for 0, 8, 16, 24 and 32 hours. However, a significant negative relationship between the time since ingestion and the success probability of obtaining positive PCR reactions among blood meals digested for between eight and 32 hours was demonstrated. There was no significant difference in the success probability of amplifying human DNA from blood meals of mosquitoes killed at zero and 8 hours after ingestion. The research demonstrated that not the quality of ingested blood, but the time since ingestion determined the success of blood meal analysis.

    Host characteristics and differential attractiveness of humans to An. gambiae (Chapter 4, 5 & 6)

    A tent olfactometer that accommodates complete humans as sources of host-seeking stimuli was designed, developed and tested. The olfactometer was used to study (1) differential attractiveness of humans to host-seeking An. gambiae and (2) how the differences, so elicited, are affected by human breath, body odour, heat and moisture. Nine human subjects were successfully ranked for their attractiveness to the mosquitoes based on (mosquito) responses to their complete body emanations encompassing body odour, heat and moisture. The nine subjects were classified into least (3 persons), medium (4 persons) and most attractive groups (2 persons). Breath was shown to reduce mosquito responses, whereas body odour was highly attractive. Breath was also shown to be an important contributor to between-person differences in relative attractiveness to An. gambiae . Whereas differential attractiveness of two human subjects for the mosquitoes could be demonstrated based on their total body emanations (breath plus body odour), the attractiveness of the two subjects did not differ significantly based on body odour alone. Body odour from either individual was consistently more attractive than total emanations from the other. The same results were obtained with another pair of individuals. It was concluded that breath, although known to contain attractive semiochemicals like carbon dioxide, may also contain compounds that inhibit attraction and may thus serve as an important contributor to between-person differences in relative attractiveness to this important malaria vector. The inhibitory effect of breath was postulated to be allomonal as it benefits the emitter (human being) but does not harm the recipient (mosquito vector). Body heat and moisture were shown to have significant effects on the attraction of An. gambiae to humans. In general, An. gambiae was more attracted to the individual whose body emanations were warmer but less moist than those of an opposing counterpart, in choice experiments. It was concluded that body heat and moisture influence host-selection by An. gambiae at short range and that their effect is probably achieved through interaction with breath components.

    Parasite infection and differential attractiveness of humans to An. gambiae (Chapter 7 & 8)

    A rare window of opportunity allowed for the investigation of the effect of clinical symptoms and parasitaemia due to Plasmodium falciparum on variability in human attractiveness to the malaria mosquito An. gambiae using the tent olfactometer previously developed. The relative attractiveness of an individual who was always more attractive than a specific counterpart (when both were uninfected) was suppressed when he (the 'putatively' more attractive individual) displayed clinical symptoms (fever and profuse sweating) of malaria caused by P. falciparum . This finding provided both new and alternative evidence, within the intricate web of Anopheles-Homo-Plasmodium interactions, that the malaria parasite P. falciparum influences the olfactory signals produced by human hosts. Field studies, in which a twin pair of male humans was recruited as a follow-up to the olfactometer study, found that being positive with malaria parasites (trophozoites and possibly gametocytes of P. falciparum ) is associated with higher numbers of attracted mosquitoes ( An. gambiaesensu lato ). This effect was not a consequence of the time of the year and the higher number of mosquitoes present in that period. It was recommended that further investigations be carried out. If these results are confirmed to be true, this work will constitute the first evidence that P. falciparum is capable of enhancing its own transmission by manipulating the physico-chemical characteristics of its vertebrate hosts in such a way that infected individuals are preferentially selected as blood meal sources by host-seeking malaria vectors.

    What questions remain unanswered (Chapter 9)

    Much as this thesis has provided some answers to why humans differ in their degrees of attractiveness to mosquitoes ( An. gambiae ), many more questions remain unanswered. The key questions in point include the following: (1) How can we tell whether one is more or less attractive to host-seeking mosquitoes? (2) How do parasites affect the host-seeking behaviour of their insect vectors? and (3) How do evolutionary processes related to host-seeking behaviour affect the fitness of mosquito vectors? The answers to these questions and those to a myriad of others are still waiting to be resolved.

    Aromaonderzoek in de lift
    Kan, E.J.M. van; Boelrijk, A. - \ 2000
    Voedingsmiddelentechnologie 33 (2000)14/15. - ISSN 0042-7934 - p. 28 - 29.
    sensorische evaluatie - organoleptische kenmerken - geur en smaak - geurstoffen en smaakstoffen - aromatische stoffen - reuk - smaak - voedselindustrie - voedseltechnologie - productontwikkeling - consumenten - consumentenvoorkeuren - aroma - chemotaxis - sensory evaluation - organoleptic traits - flavour - flavour compounds - flavourings - smell - taste - food industry - food technology - product development - consumers - consumer preferences - aroma - chemotaxis
    Verslag van het in mei gehouden minisymposium te Wageningen. Het werd georganiseerd door de Vereniging voor Voedingsleer en Levensmiddelentechnologie
    Olfaction in the malaria mosquito Anopheles gambiae : electrophysiology and identification of kairomones
    Meijerink, J. - \ 1999
    Agricultural University. Promotor(en): J.C. van Lenteren; J.J.A. van Loon. - S.l. : S.n. - ISBN 9789058081179 - 139
    anopheles gambiae - reuk - kairomonen - elektrofysiologie - identificatie - anopheles gambiae - smell - kairomones - electrophysiology - identification

    Female mosquitoes of the species Anopheles gambiae Giles sensu stricto are important vectors of human malaria in Africa. It is generally assumed that they locate their human host by odours. These odours are detected by olfactory receptor neurons situated within cuticular extensions on the antenna. These cuticular extensions, called sensilla, contain numerous pores through which the odours can enter the sensillum and reach the olfactory receptor neuron membrane. Despite the fact that these mosquitoes are so important for the transmission of malaria, hardly any sensory studies have been performed to date. Therefore, the goal of this study was to analyze the response spectra and characteristics of the olfactory receptor neurons encoding human-derived odours in female An. gambiae . Another goal of this study was the identification of human odours which guide female An. gambiae to its host. This was accomplished by making chemical analyses of the odour profile of human sweat.

    Firstly, a scanning electron microscopic (SEM) study was undertaken to identify the different types of sensilla exhibited on the antennae of female An. gambiae . Chapter 2 shows SEM photographs of the six different types of antennal sensilla: large and small sensilla coeloconica, grooved peg sensilla, sensilla trichodea, sensilla ampullacea and sensilla chaetica. The distribution of the different sensilla on the thirteen segments is tentatively described. Odours present on the human skin or identified in the headspace of human sweat evoked responses of grooved peg- and sensilla trichodea receptor neurons (chapter 4 and 6). Although the grooved peg sensillum is easily recognized during SEM studies and light microscopic observations, the different subtypes of sensilla trichodea are hard to distinguish in An. gambiae . SEM photographs of two different types of sensilla trichodea housing receptor neurons responsive to sweat-borne components are shown in chapter 2.

    The antennal olfactory responses of female An. gambiae were studied by means of electroantennography (chapter 3). The electroantennogram (EAG) is considered to be the summed activity of all (or a part of the) responsive sensory receptor neurons on the antenna. Initially, the technical aspects of the EAG recording technique were closely examined. It was found that when using tungsten electrodes, artefactual electrode potentials were generated by the carboxylic acids, propionic acid, butyric acid and hexanoic acid. No artefactual electrode potentials were obtained with glass electrodes. A blend of carboxylic acids has been reported to be attractive for female An. gambiae mosquitoes. These are present on the human skin where they display an enormous diversity in chemical structure. To quantify the antennal olfactory sensitivity to carboxylic acids, EAG studies were conducted with glass electrodes. Carboxylic acids with carbon chain lengths of 5-8 (C 5 -C 8 )elicited high EAG amplitudes, while lower responses were evoked by the less volatile acids, C 9 -C 14 . Hexanoic acid evoked the highest EAG response.

    Single sensillum studies were undertaken to reveal antennal olfactory receptor neurons responsive to carboxylic acids (chapter 4). Neurons innervating one or two of the morphologically different subtypes sensilla trichodea were found to respond to the short chain carboxylic acids: acetic acid (C 2 ), propionic acid (C 3 ), butyric acid (C 4 ), iso-butyric acid (iC 4 ) and iso-valeric acid (iC 5 ). Usually the receptor neurons responded by inhibition, but receptor neurons were also found responding by excitation to the short chain carboxylic acids. Occasionally receptor neurons were found which responded by excitation to 1-octen-3-ol. Dose-response characteristics were assessed for the carboxylic acid-inhibited cell type. It was demonstrated that the carboxylic acid-inhibited neuron was equally sensitive to the short chain acids tested. This was revealed by making corrections for the differences in volatility of the different short chain acids. It is suggested that in this case an inhibitory response might function to block the response of a specialised cell normally responding by excitation to other stimuli (chapter 7).

    Because behavioural studies indicated that in addition to carboxylic acids other components are involved in the host-seeking behaviour of female An. gambiae , studies were undertaken to identify new putative attractants (chapter 5). Rather than searching for minor differences in chemical odour profiles between different individuals, we focussed on components which are generally produced by every human host. Freshly collected pooled sweat samples obtained after physical exercise from a group of volunteers neither attracted female An. gambiae in a windtunnel bioassay, nor evoked a detectable EAG response. Incubation of the sweat samples, however, resulted in a behaviourally attractive source of volatiles which evoked reproducible EAG responses. Sweat obtained during physical exercise is most likely to originate from the eccrine and sebaceous glands. Several observations strongly indicated that during incubation attractants are produced by microbial activity. Although the fresh sweat did not elicit a behavioural or EAG response, it was possible that it may contain components which acted as synergists at the behavioural level together with components produced during incubation. Headspace analysis of the fresh and incubated sweat revealed that geranyl acetone (5%-6%) and 6-methyl-5-hepten-2-one (1.8%-1.9%) were relatively abundant in both the fresh and incubated headspace samples. Headspace samples of the incubated sweat comprised large amounts of indole (27.9%), 1-dodecanol (22.4%) and 3-methyl-1-butanol (10%). These components were absent or only present in minor amounts in the headspace samples of the fresh sweat. Indole, geranyl acetone and 6-methyl-5-hepten-2-one evoked an EAG response, while 1-dodecanol did not elicit any response. 3-Methyl-1-butanol was only tested at the single cell level (chapter 6).

    In order to reveal olfactory receptor neurons responsive to the identified sweat-borne components, studies were conducted at the single cell level (chapter 6). For other mosquito species, such as Aedes aegypti , the grooved peg sensillum is considered to house receptor neurons sensitive to host odours. Indeed, incubated sweat elicited excitation of a receptor neuron innervating a subpopulation of the grooved peg sensilla in An. gambiae . The same receptor neuron was excited by ammonia, which was found to be present in large amounts in the incubated sweat. This strongly implies that ammonia is causing (most of) the attractiveness of the incubated sweat.

    However, chemically identified components from the headspace of the fresh and incubated sweat (chapter 5) did not elicit responses of grooved peg receptor neurons. They evoked excitation of receptor neurons associated with the sensilla trichodea. Two different subpopulations were found, one was innervated by receptor neurons sensitive to indole, while the other subpopulation housed receptor neurons sensitive to geranyl acetone. 3-Methyl-1-butanol and 6-methyl-5-hepten-2-one elicited responses of receptor neurons associated with both subpopulations. Receptor neurons displayed lower sensitivity to 3-methyl-1-butanol and 6-methyl-5-hepten-2-one. Sensilla trichodea receptor neurons only occasionally responded to the source of the components, the incubated sweat.

    It is suggested that not only the grooved peg receptor neurons encode host-odours but also the sensilla trichodea receptor neurons fulfill a function. The incubated sweat may evoke an increase in the spike frequency of only a few spikes per second and responses like these are very hard to detect. Another explanation might be that sensilla trichodea receptor neurons encode other behavioural activities, such as nectar feeding or location of oviposition sites. Identified sweat-borne components are very likely of microbial origin. Microbial products are very common in nature and therefore not restricted to human emanations (chapter 6).

    Further studies on the behavioural level might elucidate the role of the identified sweat-borne components for the behaviour of An. gambiae . The function of the different olfactory receptor neurons in host-seeking An. gambiae is further discussed in chapter 7.

    The behaviour of tsetse flies in an odour plume
    Groenendijk, C.A. - \ 1996
    Agricultural University. Promotor(en): J.C. van Lenteren; W. Takken. - S.l. : Groenendijk - ISBN 9789054855217 - 162
    Anthomyiidae - Muscidae - Drosophilidae - Calliphoridae - Agromyzidae - Tachinidae - Glossinidae - Tephritidae - dieren - voedingsgedrag - diergedrag - chemotaxis - reuk - smaak - Glossina - schizophora - Anthomyiidae - Muscidae - Drosophilidae - Calliphoridae - Agromyzidae - Tachinidae - Glossinidae - Tephritidae - animals - feeding behaviour - animal behaviour - chemotaxis - smell - taste - Glossina - schizophora

    The tsetse flies Glossina pallidipes Austen and G. m. morsitans Westw. (Diptera: Glossinidae) are obligatory blood feeding insects that do not live in close association with their hosts (mainly mammals). Tsetse flies are relatively long lived insects and have to take a blood meal regularly. Tsetse flies use smell and vision to find their hosts. In the last decade, many aspects of tsetse foraging and host-location behaviour have been elucidated. A range of kairomones has been identified. These kairomones can be used to which increase the number of tsetse caught with a trap or a target. However, some aspects of tsetse behaviour remained unclear. Not much known about the effects of the identified kairomones on the host-location behaviour of tsetse at long distance for example. Also, the effect of the physiological state of a tsetse on its foraging behaviour, was unclear.

    This thesis describes a field study, conducted in the Zambezi valley, Zimbabwe, that aimed at clarifying these questions. Chapter 2 and 3 describe studies of the foraging behaviour of tsetse. Studies of tsetse host location behaviour are presented in the following five chapters.

    Foraging behaviour

    In the field, G. pallidipes and G.m. morsitans are mostly caught in the early morning and the late afternoon. Spontaneous activity of G. morsitans in the laboratory also showed peaks in the morning and evening. How the activity patterns in the field are and what the effects of sampling methods on the apparent rhythm are, was not clear, however. In chapter 2 , 1 describe studies in the diurnal rhythm in catches with different devices.

    From before sunrise until after sunset, hourly catches of G. m. morsitans and G.pallidipes were made from a stationary unbaited electric net; an ox flyround; an electrified target; an epsilon trap and a biconical trap. The latter three were baited with artificial host odour, consisting of acetone, 1-octen-3-ol (henceforth termed octenol), 3-n-propylphenol and 4-methylphenol.

    Catches of tsetse were low from dawn to early afternoon, peaking just before sunset. Despite the broad similarity in diurnal patterns, there were some consistent differences between the sampling methods. The fraction of the daily catch caught in the afternoon with the target or the traps was larger for males than for females. The catch at the unbaited electric net probably gave the best estimate of the diurnal rhythm of flight activity of tsetse. Compared to the net catch, trap catches of tsetse were relatively high during the middle of the day and low in the early morning and late afternoon. The differences were attributed to sampling biases of traps. The pattern of the target catches was not significantly different from the pattern of unbaited net catches. The catch pattern at the mobile bait was significantly different from that of the net. This is attributed to the response of tsetse sitting on vegetation, which were not sampled by the unbaited net, to the ox fly-round. It is concluded that target catches can be used to monitor diurnal rhythms in tsetse activity. The pattern of Stomoxynae -catches on targets resembled that of tsetse. However, no peak was evident in the electric net catches. Catches of the tabanid Philoliche (Stenophara) zonata Walker showed a sharp peak in the early afternoon.

    The daily patterns in catches at the unbaited net and the baited target were similar. This suggested that active search was the most important strategy for tsetse to find a host. In chapter 3 , the catches of targets and unbaited nets and the tsetse sitting on vegetation were studied in more detail to obtain evidence for this suggestion.

    The catches of G.pallidipes and G.m. morsitans at a target baited with odour (acetone, octenol and two phenols) were positively correlated with catches of the same species at an unbaited net. No correlation existed between target catches and hand net catches of tsetse flies sitting on the vegetation. G.pallidipes females caught at a target and at an unbaited net were older than those caught from vegetation. Of the female G.pallidipes caught at the target, 46 % were in the first 3 days of pregnancy. Of those caught at the unbaited net, significantly fewer, 21 %, were in this stage. G.pallidipes males caught from vegetation contained more fat (3.07 ± 0.333 mg) than those caught at the unbaited net (2.06 ± 0.339 mg) or at the target (2.19 ± 0.218 mg). The target catches consisted mostly of tsetse that were already in flight when they sensed the stimuli from the target. Target catches were biased towards female G.pallidipes in the first 3 days of pregnancy.

    Host-location behaviour

    To investigate the effects of odour composition and odour release rate on hostlocation behaviour of tsetse, mark-release-recapture studies were used. Before these experiments were started, the behaviour of tsetse just after their release was studied at 10 m downwind of an odour source with a video camera and with electric nets. This work is described in chapter 4 . Tsetse were collected with traps, marked and released. Only tsetse that were recaptured on the same day were analyzed. The study focused on G.pallidipes, because it is more readily caught in traps than G.m. morsitans.

    Video studies showed that in the absence of odour, 46 % of the released G.pallidipes turn downwind and 32 % turned upwind. Tsetse left the release box at a constant rate and appeared to avoid each other. When an artificial odour mixture containing carbon dioxide, acetone, octenol and phenols was used, 35% turn downwind, significantly less than in the absence of odour, and 37 % turned upwind. Tsetse left the release box later than in the absence of odour and not at a constant rate. Tsetse did not avoid each other.

    When the release box was placed in a complete ring of electrified nets, only natural ox odour changed the distribution of tsetse over the electric nets compared to the no odour treatment. The artificial odour mixture, with and without carbon dioxide, had no effect on the distribution of tsetse over the electric nets. Most tsetse were caught while flying in a downwind direction.

    The electric nets have an efficiency of about 50 %. In this experiment, with a complete ring of nets, the tsetse that survive their first contact with the net, could thus be killed on another net. The difference between the video study and the electric net study is attributed to this effect. The small differences between the odour treatment and the control was probably due to frequent changes in wind direction. Odour did not always reach the box because of these changes. However, if odour is present at the box, tsetse released or departing from the box react to the presence of odour immediately.

    Marked G.pallidipes were released downwind of an odour source and the percentage recaptured at the source on the same day was measured. The influence of release distance, odour composition ( chapter 5 ) and odour release rate ( chapter 6 ) on the recapture percentages were studied.

    In the absence of odour, 1.3 % of the marked tsetse released from a box or refuge were recaptured, independent of the distance between release point and odour source. When natural ox odour or a blend of carbon dioxide, acetone, octenol and phenols was dispensed, untransformed recapture percentages of box-released tsetse decreased from 18 % for tsetse released at 10 m to 2 % for tsetse released at 100 m. Recapture percentages were significantly higher than in the absence of odour at all release distances for ox odour and for release distances up to 75 m downwind for the artificial odour. When a combination of acetone, octenol and phenols or carbon dioxide on its own was dispensed, recapture percentages decreased from 6 % for tsetse released at 10 m to 0 % for tsetse released at 100 m. With these odours, recapture percentages were higher than in the absence of odour when tsetse were released at 20 m from the source, but were lower than recaptures in the presence of ox odour or the artificial mixture with carbon dioxide. Recapture percentages of flies leaving a refuge were higher than those of box-released tsetse. Proximity of source had no effect on the recapture percentage of refugeleaving tsetse.

    The odour mixture consisting of carbon dioxide, acetone, 1-octen-3-ol and phenols was released at three different rates. The medium odour release rate, was identical to the rate used in the comparison of odour composition and the results were similar. The low odour release rate, a quarter of the medium rate, only attracted tsetse from 20 m and less; the recapture percentage declined from 5% at 10 m to 2 % at 30 m. The decrease in odour release rate thus caused a decline in plume length and a decline in host location efficiency or recruitment of tsetse to the plume. When the medium release rate was increased fourfold, the resulting high odour release rate did not increase the recapture percentages from the same distances, nor did the distance from which tsetse were recaptured increase, compared to the medium rate.

    From the experiment described above, we can conclude that: (1) tsetse have an efficient host-location mechanism, 80 to 100 % of the tsetse that detect the odour at less than 30 m from the source found the source; (2) tsetse can detect an ox at 100 m distance downwind.

    An odour plume consists of 'pockets' of odour that are moved by the wind. The flux of kairomones in an 'odour pocket' might be the only cue used by tsetse. The flux is determined by the dose and the number of kairomone compounds present in the mixture. The number of kairomone compounds in the odour pocket seems to be more important than the dose of the components.

    To elucidate the differences in recapture percentages between different odour treatments, I studied the effects of odour composition on the flight behaviour of released tsetse. This work is described in chapter 7 .

    Marked G. pallidipes were released from a box at 10, 20 and 30 m downwind of an odour source. Tsetse were recaptured the same day on a 9 m wide wall of electric nets at 4 m upwind of the release box, or at the inside of an incomplete ring of eight nets at 4 m around the box. The incomplete ring was only used when tsetse were released at 10 m downwind of the source. Four odours were tested: natural ox odour; an artificial blend of acetone, octenol and phenols; the same blend with carbon dioxide and carbon dioxide alone.

    When tsetse were released at 10 m downwind of a source of natural ox odour, they avoided flying upwind. Dense vegetation did not influence their flight direction. Artificial odour did not influence the flight direction of tsetse released at 10 to 20 m downwind of the source in open vegetation, but tsetse avoided entering dense vegetation and preferred flying into crosswind oriented 'game trails'. About 35 % of the recaptured tsetse released at 30 m from the source of the artificial blend with or without carbon dioxide, flew within 20° of the prevailing wind direction. Tsetse released in the absence of odour or in the presence of the other odours flew away at random.

    The results suggest that tsetse change from straight fast upwind flight to more sinuous and slower flight when the flux of kairomones increases.

    In chapter 8 I studied the effect of the physiological state of tsetse on their host-location behaviour. G.pallidipes were marked and released from refuges and boxes placed at 10, 20 and 30 m downwind of an odour baited visual target. The physiological state of all tsetse recaptured on the same day, samples of the populations from which the marked tsetse originated and a sample of unmarked tsetse caught together with the marked tsetse, was assessed by analysis of their fat and haematin content. Before fat and haematin analysis, the females were dissected to determine their ovarian age and pregnancy stage.

    Unmarked tsetse caught with a target had on average fed 2.5 days previously. Among the females from the refuge, the variance in haematin decreased with progressing pregnancy. Females in the last stage of their pregnancy all had a high haematin content, indicating that most had fed less than 24 h ago before being captured. Tsetse recaptured from the refuge had a higher haematin content than unmarked tsetse. Recaptured refuge- leaving females were younger than unmarked females. The fat and haematin content were not related to the distance from which females were recaptured with the target. The females caught at a target baited with acetone, 1-octen-3-ol and phenols contained less fat than females caught at a target baited with the same odour plus C0 2 . The fat content of recaptured males leaving from a refuge, increased with distance of release. There was no such correlation with boxreleased males.

    It appears that haematin or the time since the last blood meal controls the search strategy of tsetse. Resting tsetse with high energy reserves will feed from a host that comes close by, but do not search actively for a host. The fat content, and in females also the pregnancy stage, influence whether tsetse will take a blood meal from a host that has been found.

    The research described in this thesis has resulted in an improved understanding of the foraging and host location behaviour of tsetse. It is now clear that tsetse can detect a host at 100 m distance and that long range host location behaviour of tsetse is influenced by odour flux rather than individual kairomones in the odour mixture. Furthermore, the effect of the physiological state of the tsetse on its behaviour is now more clearly understood. Targets do not catch all tsetse that are searching for a host. To ensure success, target control operations must be sustained, even when stationary baits no longer catch tsetse.

    Methodologische aandachtspunten bij GC-olfactometrie.
    Kleykers, R.W.G. ; Schifferstein, H.N.J. - \ 1995
    Voedingsmiddelentechnologie 28 (1995)21. - ISSN 0042-7934 - p. 26 - 29.
    chemische samenstelling - voedingsmiddelen - gaschromatografie - geurstoffen - organoleptische kenmerken - sensorische evaluatie - reuk - chemical composition - foods - gas chromatography - odours - organoleptic traits - sensory evaluation - smell
    Het identificeren van belangrijke geurcomponenten van voedingsmiddelen met behulp van gaschromatografie
    Flavour release from dried vegetables
    Ruth, S.M. van - \ 1995
    Agricultural University. Promotor(en): A.G.J. Voragen; J.P. Roozen. - S.l. : Van Ruth - ISBN 9789054854685 - 227
    tuinbouwgewassen - organoleptische kenmerken - sensorische evaluatie - reuk - geurstoffen - voedingsmiddelen - voedselbewaring - drogen - horticultural crops - organoleptic traits - sensory evaluation - smell - odours - foods - food preservation - drying

    The research described in this thesis was focused on the development of an in vitro model system for isolation of volatile compounds from dried vegetables under mouth conditions, such as volume of the mouth, temperature, salivation and mastication. Instrumental analysis of these volatile compounds by gas chromatography (GC), combined with mass spectrometry, flame ionisation detection (FID) and sniffing port detection (SP) was correlated with descriptive sensory analysis. Dried vegetables were subjected to these techniques in order to study three aspects. (1) Factors influencing flavour release from dried vegetables under mouth conditions. (2) Suitability of three types of the model system for simulation of flavour release in the mouth. (3) Characterisation of the flavours of rehydrated vegetables, as influenced by cultivar, origin, storage and rehydration conditions.

    Flavour perception, physical aspects of flavour release, flavour analysis and factors affecting the flavour of dried vegetables, including literature concerned were discussed briefly in Chapter 1 . The thesis was outlined at the end of this chapter.

    Three types of the mouth model system were introduced in Chapter 2 and compared for flavour release from rehydrated bell peppers. Release was largest in the 'purge-and-trap1system, followed by the 'dynamic headspace and mastication, (DHM) and dynamic headspace' system, respectively.

    Flavour release influenced by the composition of artificial saliva was studied for bell peppers in Chapter 3 and for French beans in Chapter 4 . Influence of saliva volume on the flavour release from French beans was studied in Chapter 4 as well. Saliva component mucin mainly decreased flavour release in both vegetables, because of flavour~ protein interactions, a similar effect showed α-amylase in bell peppers. Release in French beans was generally increased by α-amylase, probably due to degradation of inclusion complexes of starch. Decrease in flavour release from French beans by saliva volume was evaluated in a model study. GC/SP patterns of odour active compounds were hardly influenced by both saliva composition and volume.

    Chapter 5 revealed that flavour release from rehydrated French beans, red bell peppers and leeks in the DHM model system did not differ significantly from their release in the mouth of 12 assessors. These assessors released volatile compounds with different efficiencies, but they showed a statistically consistent efficiency in flavour release across the vegetables.

    The flavours of the three rehydrated vegetables mentioned above were characterised by GC/SP of volatile compounds released in the DHM model system and by descriptive sensory analysis (Chapter 6). A common odour profile was shown in the vegetables, comprising each of the odour active compounds present in French beans. correlation of rehydrated vegetables with sensory attributes and volatile compounds showed considerable contribution of volatile compounds to the flavour of rehydrated vegetables.

    The flavours of commercially dried bell peppers (origins Chile, Hungary and Turkey) were evaluated by GC/SP and descriptive and hedonic panels ( Chapter 7 ). Although the three origins differed substantially in FID patterns, GC/SP patterns and scores for 'odour' attributes in sensory analysis were hardly different. Differences in appreciation between Chilean and Turkish bell peppers are therefore expected to be due to differences in 'taste' attributes (sour, bitter, sharp and pungent).

    The influence of storage conditions (water activity (aw), temperature and light) on the flavour of dried French beans was studied in Chapter 8 . Elevated temperature at aw 0.3 and 0.5 resulted in an increase in the number of assessors perceiving chemical, rotten odours in GC/SP and in an increase in scores for 'chemical', 'burned', 'musty' and ,bitter, attributes in sensory analysis. Light exposure at aw 0.1 resulted in an increase in the number of assessors perceiving chemical odours at the sniffing port and in increased scores for 'chemical, and 'burned' attributes in sensory analysis. French beans stored at 200C were more appreciated by the hedonic panel than those stored at 400C (absence of light, aw 0.3). Relationships between differently stored French beans, sensory attributes and volatile compounds indicated the latter compounds to be responsible for the difference in flavour and appreciation of dried French beans by storage conditions.

    The flavour of French beans influenced by rehydration conditions was described in Chapter 9 . Extended rehydration resulted in GC/SP in increased intensity for 2-butenal, 2methyl -2 -butenal, 1-octen-3-one and one unknown compound and in increased intensities for chemical,, 'mealy', ,mushroom, and musty, attributes in sensory analysis. Both instrumental and sensory analysis of the texture revealed a gradual decrease with extended rehydration. Relationships between sensory attributes and volatile compounds showed major contribution of volatile compounds to the difference in flavour of French beans resulting from rehydration conditions.

    It can be concluded ( Chapter 10 ) that flavour release from rehydrated vegetables was influenced by both saliva composition and volume. Mouth model system DHM simulated flavour release in the mouth quite well. The flavours of dried vegetables were shown to be influenced by cultivar, origin, storage and rehydration conditions.

    Emissie van ammoniak, distikstofoxide, waterstofsulfide en geur van de beluchtings- en denitrificatieruimten van de KGBI te Ede : intern verslag
    Willers, H.C. - \ 1993
    Wageningen : IMAG-DLO (Nota / Dienst Landbouwkundig Onderzoek, Instituut voor Mechanisatie, Arbeid en Gebouwen P 93-5) - 8
    reuk - geurstoffen - emissie - gassen - ammoniak - distikstofmonoxide - zwavelwaterstof - beluchting - denitrificatie - smell - odours - emission - gases - ammonia - nitrous oxide - hydrogen sulfide - aeration - denitrification
    Olfactory control of insect behavior : neurobiological exploration of the moth's nervous system
    Hildebrand, J.G. - \ 1992
    Wageningen : Landbouwuniversiteit Wageningen - 23
    diergedrag - colleges (hoorcolleges) - Lepidoptera - feromonen - reuk - animal behaviour - lectures - Lepidoptera - pheromones - smell
    Sensorische vergelijking tussen twee partijen kerstomaten van verschillende sorteringen en ronde tomaten
    Mazijk - Bokslag, D.M. van; Cramwinckel, A.B. - \ 1991
    Wageningen : DLO-Rijks-Kwaliteitsinstituut voor Land- en Tuinbouwprodukten (Rapport / RIKILT-DLO 91.42) - 12
    solanum lycopersicum - tomaten - sensorische evaluatie - reuk - geurstoffen - solanum lycopersicum - tomatoes - sensory evaluation - smell - odours
    Twee sorteringen kerstomaten zijn door het Thuispanel en door een analytisch panel beoordeeld. Aan het Thuispanel zijn vragen over het gebruik en de smaak van de kerstomaten gesteld. Het analytisch panel heeft de kerstomaten naast ronde tomaten beoordeeld op de aspecten 'smaakgehalte, 'zoet', 'zuur', 'sappig' en 'melig'. Het analytisch panel is ook gevraagd een totaal oordeel te geven.
    Host odour recognition by the Colorado potato beetle
    Jong, R. de - \ 1988
    Agricultural University. Promotor(en): L.M. Schoonhoven, co-promotor(en): J.H. Visser. - S.l. : De Jong - 65
    chemotaxis - chrysomelidae - reuk - smaak - chemotaxis - chrysomelidae - smell - taste
    Dit proefschrift beschrijft de wijze waarop de Coloradokever een waardplantgeur kan herkennen. De geur van een waardplant wekt bij de Coloradokever een windopwaarts gericht loopgedrag op. Essentieel hierbij zijn de verhoudingen tussen een aantal algemene plantegeur- komponenten die samen de zogenaamde 'groene geur' van een plant vormen (Hoofdstuk l).

    Geurreceptoren in de antenne van de Coloradokever vertonen graduele verschillen in de mate van specialisatie op bepaalde groene geurkomponenten. De receptorrespons op een geurkomponent kan onderdrukt worden door de aanwezigheid van een tweede geurkomponent (Hoofdstuk 3). Dit fenomeen, suppressie genaamd, manifesteert zich in een mate die eerder karakteristiek is voor een receptor dan voor bepaalde kombinaties van geurkomponenten (Hoofdstuk 4). Doordat suppressie sterker optreedt naarmate een receptor meer gespecialiseerd is, ontstaan er binnen de receptorpopulatie zekere verschillen in gevoeligheid voor de hoeveelheid en de samenstelling van een groene geur (Hoofdstukken 3 en 4) .

    De scheiding van informatie betreffende geurkwantiteit en kwaliteit wordt in de antennale lob van de hersenen verder aangescherpt. Met deze twee informatiekanalen kan het centraal zenuwstelsel van de kever op een eenvoudige wijze de waardplantgeur koderen (Hoofdstuk 2; Fig.1).

    Een voedingservaring kan tot op zekere hoogte de waardering van de Coloradokever voor plantegeuren beïnvloeden. Dit verschijnsel is mogelijk voor een deel te verklaren uit een veranderde receptorgevoeligheid (Hoofdstuk 5).

    Host odor perception in phytophagous insects.
    Visser, J.H. - \ 1986
    Annual Review of Entomology 31 (1986). - ISSN 0066-4170 - p. 121 - 124.
    bibliografieën - chemotaxis - entomologie - herbivoren - insecten - plantenplagen - reuk - smaak - bibliographies - chemotaxis - entomology - herbivores - insects - plant pests - smell - taste
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