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 managing adult beetles to decrease egg deposition. The primary management tool for this approach is a commercial bait composed of a feeding stimulant (cucurbitacin), inert ingredients, and a small quantity of insecticide. Cucurbitacin-based baits have had poor residual insecticidal activity that decreases efficacy and economic practicality. These studies were designed to extend the residual activity of 2 commercial bait formulations, Slam Prader® and Slam SD® (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 lignate to have the greatest potential to provide rainfastness with a trend for less residual activity with higher concentrations (>2% of spray volume) of adjuvant. 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 formulation 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 treatments provided adequate management of the adult corn rootworm for 3 wks after application. Based on sticky trap counts, insecticide treated plots maintained beetle populations below the economic threshold of 5 corn rootworms/trap/day and significantly below the corn rootworm density in the untreated plots.