Susceptibility of Liriomyza sativae Blanchard (Diptera: Agromyzidae) populations to reduced risk insecticides

Liriomyza sativae Blanchard is a major pest of melon and other crops in the Northeast of Brazil, where it has caused great losses despite the use of insecticides to reduce infestations. Previous studies showed that Liriomyza flies can develop resistance to several groups of insecticides, making difficult its control in the field. Bioassays to estimate the concentration-mortality curves were performed to investigate the response of L. sativae populations to abamectin, spinosad and chlorantraniliprole, as well as to establish a baseline for cyantraniliprole and spinetoram. The LC50 values for abamectin varied from 2.8 (PB1 population) to 4.8 (MSR2 population) mg/L, for chlorantraniliprole from 0.5 (MSR2 population) to 15.8 (PB1 population) mg/L, for cyantraniliprole from 0.7 (MSR1 population) to 5.2 (CMSF population) mg/L, for spinosad from 1.0 (PB3 population) to 13.5 (MSR2 population) mg/L, and for spinetoram from 0.2 (PB3 population) to 0.6 (MSR2 population) mg/L. Resistance ratios higher than 10-fold were observed for the populations PB3 (12.5-fold), CMSF (12.8-fold), PB1 (34.53-fold) for chlorantraniliprole, and MSR2 population (13.1-fold) for spinosad. The highest resistance ratio for abamectin, cyantraniliprole and spinetoram was respectively 1.8-fold (MSR2 population), 7.2-fold (CMSF population) and 3.1-fold (MSR2 population). Recommended doses of abamectin and spinosad caused 100% mortality of assessed populations. Overall, enzyme activities showed no association between susceptibility and insecticides among populations but were variable among populations. Monitoring and product rotation for managing the evolution of L. sativae to resistance is recommended.