Genetic improvement of spinosad resistance in the biocontrol agent Orius laevigatus

Augmentative biological control has experienced a remarkable success, particularly in protected crops. Yet integrated pest management (IPM) still requires corrective treatments to manage some pests, which may result in detrimental effects on biological control agents (BCAs). Hence, the choice of selective pesticides is crucial for an effective pest management. A complementary approach is the genetic improvement of BCAs resistant to some key pesticides, allowing their joint use in IPM. The predator Onius laevigatus (Fieber) (Hemiptera: Anthocoridae) is widely introduced in protected crops to supress thrips and other small pests. Spinosad is a naturally derived biopesticide and a key compound in both conventional and organic crops. However, spinosad has been reported as slightly to moderately harmful to O. laevigatus. Here we explored and exploited the intraspecific variation in spinosad susceptibility in wild and commercial populations of O. laevigatus to select a spinosad-resistant strain. We found a 48.8-fold variation in susceptibility to spinosad among 35 populations, obtaining a lethal concentration (LC50) of 166.3 mg l(-1) for the baseline. A spinosad-resistant strain (SPI38) was successfully obtained (LC50- = 2110.0 mg l(-1)). The resistance was stable for ten generations without selection pressure and was expressed in all life stages, particularly from the 3rd nymphal instar to adult. SPI38 showed cross-resistance to spinetoram and inhibitors of the detoxification enzymes were not able to restore susceptibility, which suggest a target-site resistance mechanism. The resistance achieved may be sufficient to allow survival of adults and nymphs of O. laevigatus exposed to field applications of spinosad across the cropping season.