Improvement of the residual activity of a cucurbitacin-based adult corn rootworm (Coleoptera : Chrysomelidae) insecticide

Areawide management of the corn rootworm, Diabrotica spp., focuses on manag ing adult beetles to decrease egg deposition. The primary management tool f or this approach is a commercial bait composed of a feeding stimulant (cucu rbitacin), inert ingredients, and a small quantity of insecticide. Cucurbit acin-based baits have had poor residual insecticidal activity that decrease s efficacy and economic practicality. These studies were designed to extend the residual activity of 2 commercial bait formulations, Slam Prader (R) a nd Slam SD (R) (MicroFlo Co., Lakeland, FL), by adding materials as a tank- mixed adjuvant or as a part of the formulation to prevent wash-off by rain. Initial assays with Slam Prader identified low pH gluten and sodium lignat e to have the greatest potential to provide rainfastness with a trend for l ess residual activity with higher concentrations (>2% of spray volume) of a djuvant. An additional assay demonstrated that low pH gluten was effective for resisting wash-off by natural rain when added to the Slam SD as a formu lation ingredient. Large-plot experiments conducted over 2 yrs in growers' fields in northwestern Illinois failed to show a statistically significant advantage of gluten and lignin additives. For both years, all bait treatmen ts provided adequate management of the adult corn rootworm for 3 wks after application. Based on sticky trap counts, insecticide treated plots maintai ned beetle populations below the economic threshold of 5 corn rootworms/tra p/day and significantly below the corn rootworm density in the untreated pl ots.