Effects of surfactins, Bacillus lipopeptides, on the behavior of an aphid and host selection by its parasitoid

Lipopeptides extracted from the Bacillus genus are emerging biopesticides, especially in protecting crops against phytopathogens. Among the three main families of lipopeptides, surfactins have been identified as having insecticidal properties against several insect orders. However, the sublethal effects of these promising biopesticides on insect pests and their natural enemies remain largely unknown. The aim of this study was to evaluate the effects of surfactins topically applied on black bean aphid Aphis fabae mortality. First, the effects of surfactins on aphid mortality were determined by delivering increasing concentrations to adults and nymphs. Second, the sublethal effects of surfactins on locomotor activity and feeding behavior of surviving aphids were evaluated using the electropenetrography method. Finally, the effect of host exposure to surfactins on host selection behavior by Aphidius matricariae parasitoid females was analyzed.

Four surfactins concentrations were studied (0.5, 1, 2.5 and 5 g L^-1 ). There was concentration-dependent mortality in response to surfactins at 24 h after treatment. Surfactins impacted aphid behavior when delivered at 1 g L^-1 by inducing a greater locomotor activity and a reduction in feeding activity. By contrast, at the third trophic level, exposure of aphid hosts to surfactins did not affect behaviors leading to host recognition and acceptance by parasitoid females.

This study highlighted the consequences of aphid exposure to surfactins in the context of bottom-up regulation. Although surfactins could directly impact aphid behavior, they had no apparent consequences on the host selection behavior exhibited by parasitoid wasps.