Laboratory and field performance of an imidacloprid gel bait against German cockroaches (Dictyoptera: Blattellidae)

An experimental 2.15% imidacloprid gel bait containing approximately 44% water was evaluated in laboratory and field studies against the German cockroach, Blattella germanica (L). In continuous exposure tests, toxicity and presumably bait consumption varied with cockroach stage, deprivation of competitive food, and temperature. The LT50 values for cockroaches provided with competitive food ranged from approximately 0.9 h for adult females to 190 h for small nymphs. The LT50s for cockroaches not provided competitive food ranged from approximately 1.7 h for adult females to approximately 31 h for adult males. The LT50s decreased exponentially with temperature between 10 and 30 degrees C. Even though the bait was significantly more repellent (approximately 38%) than an untreated control (approximately 14%) when tested in Ebeling choice boxes, performance index values were positive and increased to nearly 100 (indicating high mortality and low repellency) after 14 d. When applied at 15-45 g per kitchen, the bait significantly reduced German cockroach trap catch in infested homes during a 4-wk period. There was a approximately 50% reduction after 1 wk and approximately 80% reduction 4 wk after treatment.