The contribution of non-consumptive effects to the biological control of pest caterpillars

The conservation biological control of caterpillar pests in crop production focuses on promoting natural enemies that reduce caterpillar abundance by consuming them. However, natural enemies that do not use caterpillars as prey, but are present foraging in the crop environment for other prey, may also contribute to caterpillar biological control by causing the caterpillars to engage in costly defensive behaviors. Such behaviors include dropping from the plant, thrashing, and curling up which could potentially have an impact on survival and, therefore, abundance. Our objective was to evaluate the intensity of the defensive behavioral response of caterpillars to natural enemies that consume them and to natural enemies that do not consume them. In the lab, we observed encounters between three caterpillar species in the family Noctuidae and two parasitoid species in the family Braconidae, one that attacks the caterpillars and one that attacks aphids. The caterpillars’ time spent feeding on the plant was lower when the aphid parasitoid was present due to foraging interactions that led to behavioral responses. The finding that caterpillars respond defensively to non-enemy parasitoids and decrease time spent feeding on crops should lead to an advanced thinking of what can be considered an agent of biological control.