Effect of selected neonicotinoid insecticides on Blissus occiduus: Spatial and temporal quantification of clothianidin, imidaloprid, and thaimethoxam in buffalograss

The western chinch bug, Blissus occiduus Barber, is a serious pest of buffalograss grown for turf, sod, and seed. Neonicotinoid insecticides are generally highly efficacious against many turf pests, including several important phloem-feeding insects. However, imidacloprid and thiamethoxam provided only moderate to poor control of B. occiduus in field studies. Interestingly, in concurrent laboratory bioassays these compounds were toxic to both immature and adult chinch bugs. This study investigated the concentration of clothianidin, imidacloprid, and thiamethoxam in buffalograss systemic leaf tissues at 3, 7, 14, and 28 days after topical applications. The relative quantity and degradation rate of these insecticides in the sampled leaf material were documented by HPLC. All three neonicotinoids were present in the assayed plant tissues, but at differing concentrations. At 3 days after treatment (DAT), imidacloprid had the highest mean insecticide concentration (14.24 µg/g of leaf material). By 7 DAT, there were significant reductions in concentrations of imidacloprid (3.25 µg/g), clothianidin (1.56 µg/g), and thiamethoxam (0.60 µg/g). At 14 DAT, the concentration of thiamethoxam (0.16 µg/g) was significantly less than imidacloprid (0.77 µg/g) and clothianidin (0.66 µg/g). By 28 DAT, imidacloprid, clothianidin, and thiamethoxam could still detected with concentrations of 0.20 µg/g, 0.19 µg/g, 0.008 µg/g remaining, respectively. Between day 3 and 28, thiamethoxam concentrations declined by 700-fold, whereas imidacloprid and clothianidin had declined only 70-fold and 60-fold, respectively. This study is the first to document the relative concentrations of topically-applied neonicotinoid insecticides in buffalograss systemic leaf tissues.