Effects of mutualistic interactions on the trophic structure of insect food webs: an ant -aphid- parasitoid food web as a model system

• Applicant: Dr. Dirk Sanders
• Subject Area: Sensory and Behavioural Biology
• Term: from 2009 to 2011
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 126033453

The structure of food webs is important for stability and function of ecological systems. The interplay of mutualistic and antagonistic interactions within food webs is crucial for understanding food web dynamics. We want to study the effect of a mutualistic interaction on the trophic structure of an insect food web. Many ant species tend honey-dew producing aphids and reduce levels of parasitism and predation on the tended aphids. There is a large guild of insect parasitoids that depend on aphids as host. Beside the primary parasitoids, there occur two groups of secondary parasitoids: the hyperparasitoids which oviposit in the primary parasitoid larvae in the still living aphid, and the mummy parasitoids which attack the pre-pupa of the primary parasitoid in the mummified aphid therefore imposing mortality also on the hyperparasitoids. Ants play a significant role in this interaction because in contrast to the mummy parasitoids, many primary parasitoids and hyperparasitoids are highly specialised and have evolved mechanisms of dealing with ants. A shift from hyperparasitoids to mummy parasitoids in the absence of ants results in stronger connections to the rest of the food web, with implications for community stability and ecosystem functioning. In order to evaluate the impact of ants on these food web interactions we will manipulate the access of two ant species to aphid colonies by exclusion in the field. The mummies will be collected to score the levels of hyperparasitism and mummy parasitism. With a new DNA based identification of parasitoids it is possible to study such complex food web interactions in depth. A diagnostic PCR on mummies from which a mummy parasitoid has emerged will detect whether it also contained a hyperparasitoid, which is a direct evidence for tertiary parasitism. To evaluate how to obtain enough hyperparasitoid DNA we will create tertiary parasitized mummies in the laboratory and test the success rate of the molecular methods.

• DFG Programme: Research Fellowships
• International Connection: United Kingdom
• Host: Professor Dr. Frank Van Veen