|Title||Foraging under incomplete information: parasitoid behaviour and community dynamics|
|Source||Wageningen University. Promotor(en): L.E.M. Vet; J.C. van Lenteren; A. Hemerik. - S.l. : S.n. - ISBN 9789058084095 - 156|
Laboratory of Entomology
|Publication type||Dissertation, internally prepared|
|Keyword(s)||parasitoïden - cotesia glomerata - pieris brassicae - pieris rapae - koolsoorten - trofische graden - voedingsgedrag - populatiedynamica - landbouwkundige entomologie - insectenplagen - parasitoids - cotesia glomerata - feeding behaviour - population dynamics - pieris brassicae - pieris rapae - insect pests - cabbages - trophic levels - agricultural entomology|
|Categories||Ecological Entomology / Biological Control of Pests|
This thesis describes research on multitrophic interactions between parasitoids, herbivores and plants. These are all involved in a dynamic game of hide-and-seek. Insect herbivores may occur in different spatial distributions across plants. Some species occur in local clusters, while others have a more even distribution. Parasitoids are challenged to deal effectively with such variation in the spatial distribution of their victims. I studied how different species and strains of Cotesia parasitoids make use of chemical information and foraging experience under varying spatial distributions of hosts.
The parasitoids Cotesia glomerata and Cotesia rubecula show clear interspecific variation in foraging decisions when exploiting patches with herbivores. C. glomerata tunes its foraging decisions to the current environment as it gains experience with hosts during subsequent patch visits. In contrast, foraging decisions in C. rubecula seem insensitive to acquired experience. These Cotesia species prefer different herbivore species, that occur in different spatial distributions across plants. C. glomerata prefers to attack Pieris brassicae , that occurs in rare clusters of highly variable density. The parasitoid C. rubecula specialises on Pieris rapae that mostly feeds solitarily on plants. This leads the parasitoid C. glomerata to experience a more variable environment, with a wider scope for increased efficiency through learning.
Both Pieris species are present in Europe, but the clustered host is absent in North America. The parasitoid C. glomerata was introduced to North America in 1883 to control solitarily feeding Pieris rapae , and about 350 generations of C. glomerata parasitoids have now foraged there. The experimental results suggest that American C. glomerata have adapted to forage for solitary host larvae, mostly through a loss of costly traits for finding rare clustered larvae. The European parasitoids spend a lot of time on explorative flights, while their American conspecifics seem to minimise travel costs and effectively focus on the exploitation of patches with solitary hosts.
Herbivores are hard to find victims for parasitoids, and parasitic wasps may use any reliable information from the environment to locate them. Plants play a key role in providing this information. Plants may emit volatile infochemicals, when they are damaged by herbivores. Such volatiles are attractive to parasitoids and may guide them to their hosts. However, this research shows that the reliability of plant infochemicals may be very low when a complex of herbivores feeds on the plant. This is important, as plants are mostly attacked by several herbivore species, both in agricultural and natural ecosystems. The presence of nonhost herbivores causes parasitoids to waste time on damaged plants without hosts. A model study shows that the interaction between this 'wasted time' effect and herbivore diversity stabilises communities of parasitoids and herbivores. However, above a certain diversity threshold parasitoids may waste too much time on nonhost herbivores. This may lead to the local extinction of several parasitoid species. Thus, diversity may promote both stability and extinctions, when plants provide unreliable information.
This thesis shows that the flow of information between all these actors is crucial for the understanding of insect behaviour and community dynamics. This information flow involves plants, parasitoids and, surprisingly, both host and nonhost herbivores.