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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Voorbereiden op de winterslaap
Dicke, M. - \ 2006
Natura 5 (2006). - ISSN 0028-0631 - p. 138 - 139.
insecten - diapauze - biologische ontwikkeling - winter - insects - diapause - biological development
Insecten bereiden zich al vroeg voor op hun winterverblijf. Zodra wij de verwarming aanzetten, zijn vele insecten al lang breed in het warme zuiden. Sommigen ondernemen daarvoor een reis van zo'n drieduizend kilometer. Veel insecten gaan in diapauze, een soort van winterslaap. Om die toestand te bereiken moeten de insecten wel heel zeker weten dat de winter echt is aangebroken. Een ingewikkeld systeem zorgt dat het allemaal goed komt
Evaluation of Orius species for biological control of Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae)
Tommasini, M.G. - \ 2003
Wageningen University. Promotor(en): Joop van Lenteren. - [S.I.] : S.n. - ISBN 9058089002 - 215
frankliniella occidentalis - thysanoptera - insectenplagen - orius - heteroptera - anthocoridae - biologische bestrijding - diapauze - organismen ingezet bij biologische bestrijding - frankliniella occidentalis - thysanoptera - insect pests - orius - heteroptera - anthocoridae - biological control - biological control agents - diapause
Extrinsic and intrinsic control of diapause termination in the Colorado potato beetle
Lefevere, K.S. - \ 1988
Agricultural University. Promotor(en): L.M. Schoonhoven; C.A.D. de Kort. - S.l. : Lefevere - 120
Chrysomelidae - diapauze - hibernatie - aestivatie - Chrysomelidae - diapause - hibernation - aestivation
The adult Leptinotarsadecemlineata enters a winter diapause, which is mainly induced by short photoperiod. The effects of environmental factors (such as temperature, humidity, daylength and food) on the behaviour and the metabolism of some haemolymph components, as for example the juvenile hormone, were analysed in diapausing and post- diapausing females. During diapause three consecutive phases could be distinguished, based on changing response to temperature: 'diapause development' or true diapause, followed by a quiescence which is facultative, and a transient phase of post-diapause development leading to emergence from the soil (or diapause termination). After diapause, high metabolic rates are resumed and postdiapause development culminates in reproduction. The endocrine control of the termination of diapause was investigated by means of hormonal injections. Only the combined injections of 20-hydroxyecdysone and juvenile caused a temporary break of diapause only, lasting as long as the JH titre in haemolymph was high. 20-Hydroxyecdysone (20-HE) injected before JH suppresses the effects of exogenous JH on the endogenous metabolism of JH. It is suggested that 20-HE could be responsible for triggering the programme for diapause termination by the brain. Allatectomy experiments after diapause confirm the role of JH in reproduction and reveal the endocrine control of the Induction of a second diapause. The presented results corroborate the theory that the brain is the primary organ controlling diapause.

Ecological and physiological aspects of aestivation-diapause in the larvae of two Pyralid stalk borers of maize in Kenya
Scheltes, P. - \ 1978
Landbouwhogeschool Wageningen. Promotor(en): J. de Wilde. - Wageningen : [s.n.] - 110
insecten - plantenplagen - Zea mays - maïs - Tortricidae - diapauze - hibernatie - aestivatie - groei - Kenya - Pyralidae - microlepidoptera - insects - plant pests - Zea mays - maize - Tortricidae - diapause - hibernation - aestivation - growth - Kenya - Pyralidae - microlepidoptera
Stalk borers are highly destructive to a large number of important graminaceous crops all over the world. Some examples of economically important stalk borers and a general description of their life-cycle are mentioned in chapter 1. In the same chapter difficulties in controlling the insects are described. The crucial role of aestivation- diapause in the life history of tropical stalk borers is elucidated and the importance of further research on this subject is demonstrated.

Aestivation-diapause in two Pyralid stalk borers, Chilopartellus (Swinhoe) and Chilo orichalcociliella (Strand) was investigated under field and laboratory conditions.

The relation between diapause and climate during three consecutive years is described in chapter 2. Yearly and seasonal fluctuations in the larval and pupal populations of the two stalk borers in maize appeared to be considerable. As long as the water conditions for plant growth were suitable, insects had a continuous development. Under these conditions larvae had pigmented spots and could not survive dry conditions. Soon after cessation of the rains (or irrigation) rates of pupation decreased. At that time larvae lost their cuticular pigmentation and became resistant to drought. Comparison of the incidence of aestivation in the field with the prevailing climatic conditions showed that only lack of rain could be associated with the arrested larval development. No effects of temperature, relative humidity or photoperiod could be found. These results indicate that the host plant may be involved in the induction of diapause.

Chapter 3 is concerned with characteristics of pre-diapause and diapause larvae. Evidence was obtained that under natural conditions larvae do not feed during diapause as long as they are not disturbed. The physiological condition of field-collected stem borer larvae changed considerably upon entering diapause: a decreased rate of oxygen consumption, rate of heart beat and water content, an increased fat content, and arrested development of the testes were found. These changes normally occurred before larvae were turning unspotted and/or were becoming resistant to drought.

The condition of the host plant in relation to diapause induction is described in chapter 4. Diapause could be induced inside maize plants of different developmental stages. It was shown that the first (physiological) signs of the diapause syndrome appear in larvae feeding in stems containing 70-80% water and very little (< 1.3% of the fresh wt.) protein. The considerable variation in the sugar content of stems containing pre-diapause larvae suggests that sugar is not important in the induction of diapause.

Marked differences were found in the consumption and utilization of stems of maize plants in different developmental stages. Its possible relevance to diapause is discussed.

In chapter 5 experiments are described on the induction of aestivation-diapause by varying the food condition. Most early 5th instar larvae of C. partellus entered diapause after being introduced into aged maize stems containing 75% water, 8% sugar and 1.3% protein (fresh wt.). Pupation rate, cuticular pigmentation, QO 2 and water content of these larvae were
comparable to values obtained from field-collected aestivating larvae. Larvae which had developed beyond the early 5th instar were less sensitive to the diapause inducing factors of the aged maize stem : most of them pupated.

Test of 30 different diets with varying protein, sugar and water contents, indicated that diets containing 0.9-1.1% protein and 70% water were best in inducing diapause. Early 5th instar larvae on diets with the above mentioned protein content grew slowly (but reached normal weights), moulted into the unspotted form and had a retarded rate of pupation. Larvae on diets with lower protein contents hardly developed at all, whereas on diets with higher protein contents larvae pupated normally. Larvae reared on diets in which the water content had been reduced from the normal level of 86% to 70%, resulted in a
reduction of the larval water content and respiratory rate, close to values normal for field-collected diapause larvae. Evidence was obtained that larvae reared on diapause inducing diets attained a certain degree of drought resistance. Early 5th instar or younger larvae were the most sensitive stages to diapause induction by diet.

Many larvae on aged maize stems and artificial diets turned unspotted even though pupating soon thereafter. The relevance of the cuticular pigmentation as a criterion for aestivation-diapause is discussed.

The endocrine involvement in the aestivation- diapause is described in chapter 6. From juvenile hormone titre determinations and ligation experiments evidence was obtained that the diapause is regulated by an intermediate level of JH. Application of JH to non-diapause larvae prevented pupation of these larvae but did not evoke other aspects of the diapause syndrome.

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