Plant and prey consumption cause a similar reductions in cannibalism by an omnivorous bug

Cannibalism is usually more intense when other food sources are scarce, be it prey or plant-based foods. We hypothesized that feeding on plants would reduce cannibalism to a lesser extent than feeding on prey, because plants are considered nutritionally inferior compared to prey. We used the omnivorous bug Orius laevigatus Say (Heteroptera: Anthocoridae) to test this prediction. Starved female bugs were individually held with five second-instar conspecific nymphs and offered (i) Helicoverpa armigera eggs (prey); (ii) pollen (plant); (iii) H. armigera eggs and pollen (prey+plant); or (iv) no eggs or pollen. Fewer cannibalistic events and shorter feedings on conspecifics were recorded in the presence of pollen, prey or both than in their absence. Data therefore do not support our hypothesis that cannibalism is differentially affected by foods of different nutritional values. It seems that omnivorous feeding habits enable predators to sustain themselves on plant sources in the absence of prey, without the need to resort to cannibalism.