Comparing efficacy of insecticides against cabbage maggot (Diptera: Anthomyiidae) in the laboratory

Abstract

The efficacy of 29 insecticides was determined against cabbage maggot, Delia radicum (L.) through a laboratory bioassay by exposing field collected D. radicum maggots to insecticide-treated soil immediately after application. In an assay, 10 D. radicum maggots were exposed to insecticide treated soil and then efficacy of insecticides was determined using three parameters: (1) proportion of maggots on the soil surface after 24 h, (2) proportion of change in weight of turnip bait, and (3) dead maggots after 72 h. Efficacy index (scale of 0–100) was developed based on the three parameters. Efficacy index of 11 insecticides was ≥70 against D. radicum and they were zeta-cypermethrin, tolfenpyrad, fenpropathrin, clothianidin, bifenthrin, lambda-cyhalothrin, chlorpyrifos, ethoprop, thiamethoxam + lambda-cyhalothrin, pyrethrins, and oxamyl in the order of highest to lowest efficacy. There was a significant positive correlation (R2 > 0.5) among the three parameters. Furthermore, persistence of efficacy was examined on eight insecticides, where D. radicum maggots were exposed to field aged (1, 3, 7, 14, and 30 d) insecticide treated soil. Percentages of D. radicum maggots dead and on the soil surface were significantly greater when field aged soil was treated with bifenthrin, tolfenpyrad and clothianidin than other insecticides for most of the field age interval treatments. Efficacy of clothianidin did not change through field age interval treatments. The implications of these results on D. radicum management in the central coast of California are discussed.