Plant and prey quality interact to influence the foraging behaviour of an omnivorous insect, Dicyphus hesperus

The foraging behaviour of omnivores is often difficult to predict and, thus, our understanding of their role in ecosystems is limited. The majority of our knowledge about omnivores comes from studies examining their preferences for different species of plants and prey under different conditions. The potential effect of intraspecific variation in food quality on omnivore foraging behaviour has received less attention. To enhance our understanding of the foraging behaviour of omnivores, we used focal observations in the laboratory to monitor the foraging behaviour and activity budget of an omnivorous insect, Dicyphus hesperus Knight (Hemiptera: Miridae), in arenas where a single species of plant food and a single species of prey food were provided at varying levels of quality based on nitrogen content. The activity budget of D. hesperus was not balanced; it was dominated by prey feeding, followed by plant feeding and probing. Foraging behaviour of D. hesperus was affected by the interaction of prey and plant quality, such that optimal foraging theory could predict its foraging behaviour in the presence of prey reared on high N-fertilized tomato plants, but not in the presence of low N-fertilized tomato plants. Neither prey quality nor plant quality affected the rate of prey consumption or the handling time of prey by D. hesperus during the observation period. Our results highlight the complexity of omnivore feeding behaviour and indicate that feeding decisions are not based only on the prey or plant species provided, but also on the quality of those resources.