Dietary history modifies the innate responses of lady beetles (Coleoptera: Coccinellidae) to odors of their prey-infested host plants

Abstract

Oenopia conglobata (L.) and Menochilus sexmaculatus F. are two important predators of pistachio psyllid, a key pest of pistachio in Iran, the former indigenous, and the latter recently adventive. Aphis gossypii Glover infests understory plants in pistachio orchards and is used by both species as an alternative prey when psyllids are scarce. We 'conditioned' beetles by rearing them for five generations on these prey and their respective host plants (Pistacia vera L. and Curcurbita pepo L.), or on eggs of Ephestia kuehniella (Zeller) as a control, and measured the preferences of female beetles for plant and plant/prey odors in an olfactometer. When conditioned on Ephestia eggs, both species found P. vera odors attractive, but not C. pepo odors, and although both plants became more attractive when infested with prey, O. conglobata preferred pistachio/psyllid odors over cucumber/aphid odors, whereas M. sexmaculata showed no preference. Whereas conditioning on pistachio/psyllid caused O. conglobata to prefer (unfamiliar) cucumber/aphid odors, its innate preference for the former disappeared when conditioned on cucumber/aphid. In contrast, conditioning on pistachio/psyllid did not alter the innate responses of M. sexmaculata to cucumber/aphid odors, whereas conditioning on pistachio/psyllid caused odors of this complex to be preferred to those of aphid/cucumber. Thus both species exhibited asymmetric, species-specific responses to conditioning treatments that reflected both innate recognition of plant/prey odors, and some plasticity as a function of recent dietary history, which in some cases led beetles to prefer the novel (unconditioned) plant/prey complex. The observed plasticity of innate olfactory responses as a function of conditioning might be advantageous for generalist predators that must frequently switch among different prey types associated with different plants.