Project

Discipline

multitrophic interactions; induced plant defense; indirect plant-mediated effects; local adaptation; parasitoids; plant chemicals; plant-insect interactions; natural enemies; beans; insect ecology

Lead
Lay summary
A major challenge for ecologists is to understand the ecological and evolutionary mechanisms that create differences between and within species in naturally complex environments. Individuals of different species interact in local communities and can influence each other both directly, or indirectly through intermediaries. This is particularly true for the interactions among plants, insect herbivores that feed on these plants and the natural enemies of these herbivores (predators and parasitoids). Plant characteristics, such as chemical compounds not only strongly affect the performance of the herbivores, but also the performance of the natural enemies that feed on these herbivores. Furthermore, by feeding on a plant, an insect can induce the production of chemical defenses that will affect the performance of other herbivore species that feed on the same plant and of the natural enemies of these herbivores. We are testing these ideas using a natural system that comprises several species of bean plants (wild and cultivated), seed beetles that feed on the beans, and the parasitoids that develop on the larvae of these beetles. Using a highly multidisciplinary approach comprising of manipulative laboratory and field studies, this project should provide us insight into how direct and indirect interactions between insects species in natural communities affect the evolution of complex communities.In addition to this fundamental importance the study has potential for application in the development of pest control strategies. Beans are an important staple food and seed beetles can be devastating pest insects, not only on beans, but on many other cultivated grains, especially in storage situations. Adding to the knowledge of how different members of a natural community interact might help in the development of methods to better protect the beans and grains against insect pests.

Direct link to Lay Summary

Last update: 21.02.2013

Active participation

Self-organised

Number	Title	Start	Funding scheme

A major challenge for ecologists is to understand the ecological and evolutionary mechanisms that create differences between and within species in naturally complex environments. Individuals of different species interact in local communities and can influence each other’s fitness both directly, or indirectly through intermediaries. This is particularly true for the interactions among plants, insect herbivores and the natural enemies of these herbivores. Plant traits, such a chemical defenses not only strongly affect the performance of the herbivores, but also the performance of the natural enemies that feed on these herbivores. There is an increasing awareness that chemical defenses are inducible and that herbivory by one insect induces changes in a plant that affect the performance of other herbivore species that feed on the same plant. Because insect communities that feed on a particular plant species can vary considerably among different localities there will also be considerable variability in the induced plant responses that sequential herbivores are exposed to. I hypothesize that within each specific community herbivores and their natural enemies will have adapted to the plant defenses induced by earlier herbivores. As yet, interspecies effects mediated by plant defense responses have rarely taken in account the third trophic level and have not yet been studied in the context of genetic population structure. We have been studying a tritrophic system comprising several species of bean plants (wild and cultivated), bruchid beetles that feed on the beans, and the parasitoids that develop on the larvae of these beetles. We have tested the hypothesis that the host plants affect the performance, behavior and genetic structure of bruchids and parasitoids and the plants mediate the interaction between these two upper trophic levels. The results from our previous research provide mixed support for this hypothesis, mostly due to great differences across populations. These findings and the accumulating evidence for indirect interactions among sequential herbivores have led to the notion that variation in the occurrence and abundance of other herbivore species in this natural system may dictate the strength and nature of the interaction between bean plants, bruchids and their parasitoids. The proposed project will test this novel hypothesis.Two dominating herbivores that attack bean plants before the bruchids are of particular interest, the leaf beetle Epilachna varivestis and the weevil Apion godmani. The co-occurrence of these herbivores with each other and the bruchids varies considerable among populations. Therefore the system lends itself exceedingly well for studies into the plant-mediated effects among sequential herbivores. We will test the above hypothesis by determining the extent to which damage on bean leaves and seeds by the leaf beetle and/or the weevil affects the performance and behavior of the bruchid. More importantly, we will study how such effects may cascade upwards to the next trophic level. We also predict that as a result of differences in the intensity of these cascading factors in different geographic locations, we will find populations of bruchids and parasitoids that are genetically differentiated from each other, and are adapted to their local communities.Using a highly multidisciplinary approach comprising manipulative laboratory and field studies, performance and behavioral assays, as well as chemical and molecular analyses, this project should provide us insight into how direct and indirect interactions between and within different trophic levels affect the evolution of complex communities.