Dietary self-selection behaviour by the adults of the aphidophagous ladybeetle Harmonia axyridis (Coleoptera: Coccinellidae)

1. Harmonia axyridis is a generalist predator with a high range of accepted prey. Prey differ in nutritive contents, energetic values and cost associated with their capture and ingestion. As a result of selection pressures, animals will tend to hunt for their prey efficiently. In this paper we evaluated the suitability of Myzus persicae and Aphis fabae to the adults of the aulica phenotype of H. axyridis, their feeding preferences and the impact of mixed diets on their fitness. Feeding preference of predators was evaluated through their response to different relative abundance of prey. 2. Under a single diet regime, the adults of the aulica phenotype fed on more individuals M. persicae than A. fabae but consumed less biomass from the former. None of those prey affect relative growth rate and reproductive capacity of the ladybeetles. 3. Males and females present different types of response to three levels of different relative abundance of prey. While males show a constant feeding preference for M. persicae, females did not show a feeding preference (i.e. null switching response). Under a mixed diet regime, adults' voracity gradually increased as the proportion of M. persicae increased, but biomass consumed and relative growth rate was not affected. On the other hand, fecundity and fertility increased. 4. Our results suggest that H. axyridis present self-selection behaviour because they agree with the basic criteria of Waldbauer and Friedman's self-selection, i.e. (i) the animal's choice of food or nutrients is non-random, and (ii) the coccinellid benefits from self-selecting.