Abstract
Interactions between syrphid predators and their prey are poorly known. The adaptations of syrphids to aphid defences and the consequences for the evolution of life history traits in these predators especially are mostly unstudied. This is the first of two papers investigating the evolution of prey specialization in aphidophagous hoverflies. The study focuses on two questions: (1) Are differences in the body size of syrphid predators reflected in differences in the size of their prey? (2) Are differences in body size, body mass and development time of the syrphid predators correlated with the defence strategies of their aphid prey (e.g. mobility, toxicity)? Platycheirus clypeatus (Meigen, 1822), Platycheirus fulviventris (Macquart, 1829), Melanostoma mellinum (Linnaeus, 1758), and Melanostoma scalare (Fabricius, 1794), which differ considerably in their prey specialization, but are closely related, were chosen as model species. Life history data for these syrphids came from a laboratory study, and that for the aphids from a literature survey. These syrphid species can be arranged on a gradient of increasing prey specialization, from 32 prey species for the generalist M. mellinum and only 3 for the specialist P. fulviventris. Differences in prey specialization were even more evident when the defence ability of the various species of aphid prey was considered. For instance, the specialization on ant-attended aphids in M. scalare. Larvae exhibited a one or two weeks diapause which made the determination of developmental time imprecise. Body size of the predators was not reflected in that of their aphid prey. The postulated relationship between body size of the predator and the defence strategies of their prey was not supported by our data. A comparison of a wider range of syrphid species from different taxonomic groupings together with a phylogenetic correction procedure might reveal clearer trends. The second part of this paper (Dziock, in prep.) will investigate the correlation between prey specialization and reproductive strategies (i.e. clutch size, egg size and number) and will put the results into a broader framework.
Highlights
Predatory hoverflies are good models for investigating the relationships between prey specialization and life history strategies
In this study two questions will be investigated: (a) Are differences in body size/body mass of syrphid predators reflected in the differences in body size of their prey? (b) Are differences in body size, body mass, and development time of the syrphid predator correlated with the defence strategies of their aphid prey?
A comparison with the head widths measured in other studies shows some differences (Table 4)
Summary
Predatory hoverflies (subfamilies Syrphinae and Microdontinae) are good models for investigating the relationships between prey specialization and life history strategies. These include waxy secretions, toxins, hiding in galls, active defence, and recruitment of ants that are effective deterrents (Heie, 1982–1995; Malcolm, 1992; Stern & Foster, 1996; Dixon, 1998; Branquart, 1999; Elmes et al, 1999; Agarwala & Yasuda, 2001) These aphid defence strategies have lead to numerous adaptations in syrphid predators and their specialization on particular prey species. (b) Are differences in body size, body mass, and development time of the syrphid predator correlated with the defence strategies of their aphid prey (e.g. mobility, toxicity)? The second part will focus on reproductive strategies and their relation to prey specialization and present general conclusions
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