Costs and benefits of alates in a soybean aphid colony under predation

It is thought that predation is a key selective force for aphids. Adaptations to predation are common among aphid species and include a variety of behavioural and physiological responses. Summer parthenogenetic colonies of soybean aphid are composed of apterous and alate individuals, which are thought to have different ecological roles. Alate aphids are presumably able to escape from a variety of stress factors through migration at the cost of having reduced fecundity, increased developmental times and a higher risk of mortality attributed to migration. We hypothesized that these trade-offs associated with alate individuals would be outweighed by migration benefits on overall colony fitness. With a field cage experiment, we tested the effects of alate migration from a colony exposed to predation towards a predator-free space of un-infested plants on overall colony fitness (taken as a total numerical contribution over time). Under this same setup, we also compared the overall numerical contribution between colonies initiated with a mixture of apterous and alate individuals versus colonies initiated exclusively with apterous individuals. Finally we compared apterous versus alate fecundity under controlled laboratory conditions. Contrary to what we hypothesized, our results suggest that even though there is a long-term benefit of predator-free space colonization by alates, this benefit may be outweighed by alate reduced fecundity, thus, increased reproduction by apterous individuals might be a better adaptive strategy to overcome predation.