Project

Discipline

plant-herbivore interactions; plant volatiles; insect invasions; Brassica rapa; BVOCs; natural enemies; parasitoids

Lead
Lay summary
Alien interference: disruption of volatile-mediated interactions between plants and parasitoids by invasive insect herbivores Plant volatiles are of key importance for the foraging behavior of predators and parasitic wasps (parasitoids) in search of prey or hosts, and the specificity of these chemically-mediated interactions results from shared evolutionary history between the interacting species.  We propose that parasitoids can readily use plant-produced volatiles to distinguish between native hosts and non-hosts, but that invading insect herbivores may disrupt these finely-tuned interactions and negatively impact the foraging behavior of native parasitoids.  We test this hypothesis by using Brassica rapa (wild turnip) and its complex of native herbivores and parasitoids.  The effect of invasive herbivores on the foraging behavior of 4 native parasitoids will be evaluated in olfactometers by simultaneously testing parasitoid attraction to plants that are damaged by the parasitoid’s host herbivore, plants damaged by a native non-host, and plants damaged by an exotic non-host. The results will show to what extent invasive herbivores can impact chemical signaling between plants and natural enemies. Additional experiments will evaluate the relevance of these results in more natural settings and quantify the realized fitness impact of attraction to plants damaged by non-hosts on native parasitoids. The research is conducted in the context of a European-wide project that involves groups in four other countries, with the other groups studying the mechanisms of volatile emissions and evaluating the effects of invasive insects on herbivores and pollinators.  The data will be used in models to predict the overall population level consequences of the disruptive impact of invasive insects on chemically-mediated interactions between plants and insects.

Direct link to Lay Summary

Last update: 21.02.2013

Active participation

Self-organised

Number	Title	Start	Funding scheme

In the proposed project we join forces to determine how invading insects affect and disrupt the evolved communicative infochemical networks in native plant-insect communities. We will test our hypothesis with the use of two extremely polyphagous herbivores that have high potential to invade European natural and agro-ecosystems: the Egyptian cotton leafworm Spodoptera littoralis (Lepidoptera: Noctuidae) and the banded cucumber beetle Diabrotica balteata (Coleoptera: Chrysomelidae). The larvae of the former feed on the leaves and reproductive tissues of plants of at least 40 families, whereas the larvae of the latter are root feeders and have also been recorded on numerous different plant species, such as maize, beans, cotton and various cabbage species. These two major pests of crops in more tropical regions of the world have a high probability to be introduced into Europe as a result of human activity. The only current obstacle is the colder European climate, which does not yet allow them to survive the winters. This could rapidly change if the increase in average annual temperature continues.As plant model systems, we will largely focus on Brassica rapa and Silene latifolia. These plants are known to emit a range of different BVOCs, both from leaves and flowers. Among the BVOCs emitted by Brassica sp. flowers are the aromatics phenylacetaldehyde, 2-phenylethanol, benzaldehyde, a range of monoterpenes and sesquiterpenes as well as isothiocyanate28. Silene is characterized by the aromatics veratrole, phenylacetaldehyde, as well as the lilac aldehydes (monoterpenes)29. Brassica plants emit over one hundred volatiles after damage by Pieris caterpillars. These included green leaf volatiles, alcohols, and esters, as well as glucosinolate breakdown products such as isothiocyanates and nitriles30,31. In preliminary experiments we have found also considerable increase in the quantity and quantity of the BVOCs emitted by S. latifolia after caterpillar attack.We will study how the larval stages of both herbivores affect the volatile emissions of the native plants and how possible changes in the emissions affect attraction of local parasitoids and pollinators. We will also specifically study the responses of natural enemies that may follow the invading herbivores into the new habitats in order to determine how readily these “followers” adapt to novel odor cues. For S. littoralis we will also study the role of VOCs in neuro-physiological and genetic aspects of the host selection process and, using European wild and cultivated plants, we will determine how readily they will adopt novel host plants. Finally, we aim to assess the ecological and evolutionary consequences of the changes in BVOCs and insect behavior in field studies. The results of our studies will be used to provide parameter values for dynamic models that predict the ecological impact of the interference of invading insects in the native infochemical networks. Hence, the project will optimally exploit the expertise of the consortium to eventually make predictions about the indirect effects of invading insects on native plant-insect interactions. With the studies we aim to answer the following questions:1)What BVOVs are emitted by native plants in response to herbivory by invading insects and how different are these emissions from those induced by native shoot and root herbivores?2)How do native parasitoids and pollinators respond to novel volatile emissions and do the emissions interfere with the successful location of respectively, suitable hosts and flowers?3)How readily can parasitoids and pollinators adapt their responses at the individual level (associative learning) and over evolutionary time (local adaptation)?4)What are the ecological and evolutionary consequences of these changes in the infochemical web for plant gene flow, and the multitrophic foodweb associated with plants?The results of our studies will be used to provide parameter values for dynamic models that predict the consequences of interference of invading insects in the native infochemical networks. Hence, the project will optimally exploit the expertise at hand to eventually make predictions about the indirect effects of invading insects on native plant-insect interactions.