Does the grass seem greener if your field is more risky? Oviposition strategies of a chemically defended ladybird — ASN Events

Does the grass seem greener if your field is more risky? Oviposition strategies of a chemically defended ladybird (#575)

Sarah Paul 1 , Mike Birkett 2 , Martin Stevens 1 , Jason Baverstock 2 , Jon Blount 1
  1. College of Life and Environmental Sciences, University of Exeter, Penryn, Cornwall, UK
  2. BCCP, Rothamsted Research, Harpenden, Hertfordshire, UK

For oviparous insects with no post-natal care the egg is commonly the life stage most vulnerable to predation and the emerging larval stages are most at risk from resource constraint. Consequently, in order to maximise reproductive success females need to ensure that they lay eggs in low risk but high resource environments. Previous work has shown that many insect species can detect predator presence and adjust oviposition site selection accordingly. However, where predator presence coincides with abundant resources such risk avoidance strategies can come at the cost of food supply for emerging larvae, with females of multiple species avoiding ovipositing in risky environments at the expense of resource quality. What remains comparatively little investigated, however, are the strategies used by those species that are able to protect their eggs from predation, for example via chemical defence, as well as avoiding it. Female 2-spot ladybirds (Adalia bipunctata) produce eggs containing the alkaloid, adaline, which is toxic to the harlequin ladybird (Harmonia axyridis) larvae that predate upon them. The adult and larval ladybirds of both species feed on aphids and consequently resource abundance and predation risk are tightly linked. Using a crossed resource x risk design - where pea aphids (Acrythosiphon pisum) are the resource and harlequin larvae the predators - we demonstrate that aphid abundance and not predation risk affects A. bipunctata oviposition timing, location and likelihood as well as egg toxin level, whereas the reverse is true for the number of eggs laid. The results reflect the biological realities of the reliance of A.bipunctata on a patchily distributed and ephemeral resource for reproduction, which in turn has a strong association with the predators of its offspring.