Oviposition preference of three lepidopteran species is not affected by previous aphid infestation in wild cabbage

Several studies have shown that pre-infestation with aphids can improve plant quality for herbivorous caterpillars. This effect is often explained by the negative crosstalk between specific plant defence, signal-transduction pathways induced by aphids and caterpillars, respectively. However, in these studies caterpillars are introduced on the plants by the researcher, whereas in nature, the adult mother often chooses the food plants for her offspring. According to the preference–performance hypothesis adult females should choose oviposition sites that result in optimal performance and survival of their offspring. In this study, we investigated whether three lepidopteran species–Pieris brassicae (L.) (Pieridae), Plutella xylostella L. (Plutellidae) and Mamestra brassicae L. (Noctuidae)–prefer aphid-infested over clean plants. Adult females of the three species was given the choice between wild cabbage (Brassica oleracea L., Brassicaceae) plants infested with aphids, Brevicoryne brassicae (L.) (Hemiptera: Aphididae) for 3, 7, or 14 days vs. non-infested clean plants. Pieris brassicae females was also given the choice between plants dually infested with B. brassicae aphids and P. xylostella caterpillars when the order of infestation was varied. For oviposition, adult females of all three species did not discriminate between aphid-infested and clean plants, irrespective of the duration of aphid infestation. Also, P. brassicae females did not discriminate between sets of dually infested plants, irrespective of the order of infestation. Several mechanisms are discussed that could explain this lack of preference.