Effect of selected insecticides on Scapteriscus vicinus (Orthoptera: Gryllotalpidae) neurophysiology

Mole crickets (Scapteriscus spp.) are destructive turfgrass pests. Their tunneling and root feeding disrupt the soil surface and kill plants. Most insecticides used against them are neurotoxic and could alter their behavior, resulting in avoidance of treated areas, or increased/decreased tunneling activity. Our objective was to determine the neurotoxic effects of five insecticides (acephate, bifenthrin, fipronil, imidacloprid and indoxcarb). Toxicity bioassays were conducted to determine the lethal time (LT50) of the insecticides. Solutions of technical grade insecticides and dimetyl sulfoxide were injected into individual adult female tawny mole crickets. Mortality and knockdown effects were evaluated hourly for 12 h, then every 4 h for 7 d. Neurophysiological recordings of nerve cord spontaneous activity were conducted using a suction recording electrode in a saline solution for each specimen for the first 5 min (baseline) and for 15 min after the addition of saline, dimethyl sulfoxide (0.4%) and insecticide (10ìM). Significant neuroexitatory effects of bifenthrin, fipronil and the combination of bifenthrin and imidacloprid were demonstrated, which resulted in increased spontaneous neural activity. Bifenthrin, fipronil and the combination of imidacloprid and bifenthrin had the lowest LT50s (38.3h, 35.5h and 10.3h, respectively). Bifenthrin and imidacloprid caused immediate knockdown, but partial recovery was observed for imidacloprid. The combination of bifenthrin and imidacloprid caused immediate knockdown without recovery.