Effects of several insecticide formulations on oothecal drop and hatchability in German cockroaches (Dictyoptera: Blattellidae).

Formulations used for control of German cockroaches, Blattella germanica (L.), were investigated. The insecticides tested on gravid females were bendiocarb, chlorpyrifos, cyfluthrin, cypermethrin, fenvalerate, hydramethylnon, malathion, propetamphos, propoxur, and pyrethrins. Exposure to each insecticide increased the frequency of oothecal drop and reduced the percentage oothecal hatch. The percentage of oothecae that were dropped increased as a curvilinear function of insecticide concentration. An LD50 of propoxur to female German cockroaches resulted in the greatest oothecal drop (83.50%); fenvalerate caused the least drop (22.60%). LD50's of cypermethrin, propetamphos, and propoxur resulted in 29.60, 31.807, and 37.30% hatch from dropped oothecae, respectively. The smallest percentage hatch from retained oothecae was caused by LD50's of propoxur (1.5%) and cyfluthrin (7.70%). Retained oothecae from females treated with an LD50 of fenvalerate (68.70%) or pyrethrins (68.70%) had the greatest percentage hatch. Total percentage hatch (dropped and retained oothecae) declined exponentially as the insecticide concentration increased. An LD50 of cypermethrin limited total oothecal hatch to 24.50%, whereas LD50's of fenvalerate, malathion, and pyrethrins resulted in 53.60, 52.20, and 58.90% hatch, respectively. Mean time to oothecal hatch increased linearly with increasing insecticide concentration for all insecticides tested.