The effect of prey quality on the prey preference of Dicyphus hesperus: Are omnivores picky eaters?

The characteristics of prey that attract omnivorous predators must be known to optimize biological control programs. Prey preference research generally investigates preferences for different prey species, although within-species characteristics probably influence prey choice as well. To test this prediction, females of the omnivore Dicyphus hesperus Knight (Hemiptera: Miridae) were observed foraging on whitefly nymphs, Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae). Low and high quality whitefly nymphs were reared on tomato plants (Solanum lycopersicum L., Solanaceae) treated with 50 and 400 ppm nitrogen solutions, respectively. Rate of prey consumption was determined in no-choice arenas with 20 whitefly nymphs and prey preference was tested in choice trials where 15 nymphs of each quality were offered in patches. In all trials, females were starved for 48 hours and allowed three hours to forage. Consumption of whitefly nymphs was determined using a dissecting microscope. In no-choice trials, females consumed low quality nymphs at a greater rate than high quality nymphs, suggesting D. hesperus adjust their rate of prey intake to compensate for low nitrogen gains when feeding on low quality nymphs. In choice trials, females consumed more high quality than low quality nymphs and Chesson’s α-index indicated a significant preference for high quality prey. Therefore, female omnivores do discriminate between prey items of the same species. In a homogeneous habitat of low quality prey, this biological control agent should kill more nymphs than in a homogeneous habitat of high quality prey. In heterogeneous habitats, patches of high quality prey will be preferred.