Compensatory Feeding by Lady Beetles: Enhanced Biocontrol Potential of H. Axyridis Against Caterpillars in Salinity-Affected Agro-Ecosystems

Abstract

Effects of plant stress can cascade across trophic levels, affecting insect herbivores and their natural enemies. In this paper, we investigate the effects of salinity-induced changes to tomato fruitworm caterpillar (Helicoverpa zea) nutritional quality and their effect on the prey consumption behavior of a generalist predator (Harmonia axyridis). Using Y-tube olfactometer assays, we demonstrate that predators exhibit equal attraction to salt-stressed and non-stressed plants, irrespective of insect herbivory. We find that caterpillars feeding on salt-spiked artificial diets exhibit reduced nutritional quality, as indicated by lower protein content and higher salt content. The reduced nutritional quality of these “salty” caterpillars does not affect pre-consumption feeding behavior preferences of lady beetles but does impact predator consumption behaviors. Predators consumed a higher number of “salty” caterpillars than “non-salty” caterpillars, exhibiting a compensatory feeding response to lower nutritional quality in “salty” caterpillars. Caterpillars growing on salt-treated diets develop slower, which increases their exposure to predation. Combined with an increased consumption of “salty” caterpillars, this study demonstrates the potential of Harmonia axyridis an effective biological control agent for managing pest populations on salinity-stressed plants. Our study highlights how the effects of abiotic stress can influence predator-prey interactions.

Keywords: Insect herbivory, salt stress, predator-prey interactions, compensatory feeding