TOXICITY OF FIPRONIL TO GERMAN AND AMERICAN COCKROACHES

Topical and oral toxicity of fipronil, compared to chlorpyrifos, was d etermined for the German cockroach, Blattella germanica (L.), and Amer ican cockroach, Periplaneta americana (L.). Fipronil and Combat bait m atrices were evaluated for their attractancies to both species. In the topical toxicity tests, LD50's of fipronil, at 72 h after topical app lication, were 0.03 and 0.02 mu g/g for adult B. germanica and P. amer icana, respectively. Fipronil was significantly more toxic than topica lly applied chlorpyrifos (LD50's were 0.06 and 0.16 mu g/g for B. germ anica and P. americana, respectively). The oral toxicity of fipronil a nd chlorpyrifos in Petri dish experiments, against both species, was a ffected by stage (for B. germanica), diet concentration, and feeding a ssay. Fipronil caused higher mortality of B. germanica than chlorpyrif os in two feeding assays (continuous and abbreviated). Both compounds were equally toxic to adult males of P. americana at all rates. Fipron il caused higher nymphal mortality than chlorpyrifos 48-72 h after exp osure in both feeding assays. In large population chamber tests, fipro nil bait was more effective and faster in killing P. americana than Ra id and Combat. LT50's were 0.8, 2.4, and 7.6 d for fipronil, Raid (a.i . = chlorpyrifos), and Combat (a.i. = hydramethylnon) baits, respectiv ely. Mortality reached 96.5, 93.4, and 84.6%, respectively, at the end of the 14 d test. In the bait attractancy tests, both strains of B. g ermanica were attracted similarly to fipronil and Combat bait matrices . P. americana were attracted more to fipronil than to Combat bait mat rix or to other alternative foods.