Artificial selection for emamectin benzoate resistance in the biological control agent Orius laevigatus

Biological control is occasionally supplemented with insecticides treatments, which may have a significant impact on natural enemies. Typically, selective compounds are chosen to overcome lack of compatibility, but an alternative approach is the use of biocontrol agents resistant to pesticides. Orius laevigatus (Fieber) (Hemiptera: Anthocoridae) is the main predator used to control thrips and other small pests in greenhouses. The avermectin emamectin benzoate is a bioinsecticide developed for the control of lepidopteran pests, reported as moderately to highly toxic to O. laevigatus. Firstly, we studied the variation in susceptibility to emamectin benzoate in 32 wild and commercial populations of O. laevigatus. A 62.4-fold variation in response was found (LC50 from 0.8 mg L-1 to 49.9 mg L-1). The baseline LC50 was 4.8 mg L-1. Secondly, we exploited this intraspecific variation to select four distinct emamectin-resistant strains. After 41-47 selection cycles, four resistant strains were successfully obtained (LC50 = 104-203 mg L-1) compared to the reference population (LC50 = 4.7 mg L-1). The resistance was retained for 18 generations without insecticide exposure and was expressed in all life instars, especially from the 4th nymphal instar to adult. The emamectin-resistant strains did not show cross-resistance to abamectin. Inhibitors of the detoxification enzymes failed to restore susceptibility at the concentrations tested. Fecundity and predation capacity in the resistant strain was similar to those in a commercial population. The resistance obtained may be enough to allow survival of adults and nymphs of O. laevigatus exposed to treatments of emamectin benzoate across the crop season.