Variation in susceptibility and selection for resistance to imidacloprid and thiamethoxam in Mediterranean populations of Orius laevigatus.

Imidacloprid and thiamethoxam are neonicotinoids that have been tested in several Orius species, including Orius laevigatus (Fieber) (Hemiptera: Anthocoridae), but not the variability in their effect among Orius populations of a single species. In this study, the variation in susceptibility to imidacloprid and thiamethoxam in 30 Mediterranean wild populations and four commercial populations of O. laevigatus was investigated in the laboratory using a standard dip bioassay method. Lethal concentration values (LC50) and the mortality of adults at the maximum field rate (MFR) were calculated. The range of LC50 of thiamethoxam was from 0.7 to 5.9 mg l−1, an 8.4‐fold variability, obtaining mortality at MFR (100 mg l−1) of >89.1% in all populations. The baseline obtained a value of 2.1 mg l−1, which is very low compared to the MFR. For imidacloprid, the LC50 varied from 7.7 to 94.7 mg l−1 (12.3‐fold variability). Mortalities at the MFR (150 mg l−1) were 57.7–99.2%, that is, more variable than for thiamethoxam. The LC50 value of the baseline was 48.7 mg l−1, also low compared to the MFR. This variation was exploited to select two populations resistant to thiamethoxam and imidacloprid, respectively. Artificial selection for on average 40 cycles significantly increased the resistance to thiamethoxam (LC50 = 149.1 mg l−1) and imidacloprid (LC50 = 309.9 mg l−1). Mortalities at the MFR in the thiamethoxam‐ and imidacloprid‐resistant populations were 44.5 and 36.9%, respectively. These results demonstrate that resistance can be enhanced in biocontrol agents by artificial selection under laboratory conditions, starting with populations showing no or very low tolerance. Our neonicotinoid‐resistant populations might enhance the wider adoption of biological control by allowing punctual or hotspot applications of neonicotinoids to control several main and secondary pests. [ABSTRACT FROM AUTHOR]