Selection for resistance to pyrethroids in the predator Orius laevigatus

BACKGROUND Insecticide resistance in the natural enemies of pest species is a very desirable trait. It allows better integration of biological control with the synthetic and natural compounds applied to manage certain pests, especially secondary pest outbreaks. Insecticide resistance in predatory insects has been documented for lady beetles and lacewings, but intriguingly no cases of field-evolved resistance have been noted in any heteropteran predator. In this work, we first explored the variation in susceptibility to pyrethroids in wild and commercial populations of Orius laevigatus (Fieber). Second, we exploited this genetic variation to artificially select a strain of O. laevigatus resistant to pyrethroids. RESULTS We found significant variation [median lethal dose (LC50) 1.6-77.0 mg L-1] in susceptibility to pyrethroids in wild populations of the heteropteran predator O. laevigatus, with a baseline LC50 value of 14.6 mg L-1. We successfully selected a strain of O. laevigatus highly resistant to pyrethroids (LC50 = 1059.9 mg L-1). In addition, such resistance was expressed in every instar, particularly in the last nymphal stages, increasing the resilience of the whole population present in the crop facing pyrethroid application. CONCLUSION The level of resistance achieved may be sufficient to allow survival of adults and nymphs of O. laevigatus exposed to the maximum field rate of several pyrethroids and natural pyrethrins, widely used to control a number of pests in organic and integrated pest management crops. Therefore, this strain resistant to pyrethrins and pyrethroids would improve the resilience of biocontrol protocols, which is an urgent requirement for wider adoption of biological control.