Rate Determination, Indirect Toxicity, Contact Activity, and Residual Persistence of Lufenuron for the Control of the German Cockroach (Dictyoptera: Blattellidae)

Abstract

Three interrelated laboratory and greenhouse studies were conducted for the chitin synthesis inhibitor lufenuron to determine dose-activity, indirect toxicity, contact activity, and residual persistence against the German cockroach, Blattella germanica (L.). Lufenuron activity was determined by evaluating 3 response variables (percentage of molt inhibition, percentage of affected adults, overall percentage of mortality). These variables were unified in a dose-response rating score (the mean effects rating). In the rate determination study, differences in lufenuron activity on different surfaces (clean masonite, oily-frass masonite, unpainted plywood) had more effect on the results than did the application rate (10, 25, 50 mg/m2), life stage (3rd or 5th instars), and exposure time (15, 30, 60 min). Percentage of molt inhibition and the effects ratings were significantly greater at 25 and 50 mg/m2 than at 10 mg/m2. No differences in percentage of affected 4th instars or adults were found between 3rd and 5th instars, however, higher effects on 5th instars were observed for percentage of molt inhibition, overall percentage of mortality, and effects rating. There was a significant effect on oothecal production from females exposed to lufenuron deposit during oogenesis. The number of viable oothecae decreased, the number of aborted oothecae increased, nymphal hatch decreased, nymphal survival at 7 d after hatch decreased, and nymphal survival of the 1st molt decreased with an increase in the rate at each exposure time. In indirect toxicity tests, lufenuron activity significantly decreased with a decrease in the ratio of exposed to unexposed cockroaches. Exposure time had no effect on the indirect toxicity of lufenuron among cockroaches. In residual persistence tests, surface had more influence on the results than the environment, rate, or residual aging period. Lufenuron was most active on masonite, with deposits on plywood being more active than on oily-frass masonite. Residues aged in the laboratory were significantly more active than those aged in the greenhouse for most response variables and effects rating. A rate of 25 mg/m2 was significantly different from 10 mg/m2 for most response variables and effects rating. Effects rating reduced significantly at 6 and 12 mo of aging. Surfaces produced significant effects in all response variables until 9 mo of aging. After 12 mo, lufenuron activity on plywood and oily-frass masonite declined significantly compared with the activity on Masonite.