Laboratory evaluation of fipronil against Periplaneta americana & Blattella germanica.

BACKGROUND & OBJECTIVE In cockroach control, bait formulations are extensively used. Fipronil is one of the broad spectrum insecticides from phenyl pyrazole family available in bait formulation. The compound has been tested under field conditions. However, information on its effectiveness on different surfaces and at various density levels is not known. Therefore, the efficacy of a new formulation of fipronil 0.03 per cent (Goliath gel) was tested under laboratory conditions. METHODS The bait formulation was tested against Periplaneta americana at the dosages of 0.025, 0.05, 0.1, 0.15 and 0.2 g/m(2), and Blatella germanica at 0.025, 0.05, 0.075, 0.1 and 0.125 g/m(2) on wood, cement, mud and thatch surface with three density levels of cockroaches viz., 5, 10 and 20 numbers/m(2). Mortality after 24 h of exposure was observed daily for five days. RESULTS Rate of mortality varied between 16.0 and 96.0 per cent in P. americana and 51.0 and 100.0 per cent in B. germanica on different surfaces tested. The mortality rate of P. americana increased line rarly from the dosage 0.025g to 0.15 g/m(2) and at 0.2 g/m(2), it was independent. The LD(80) values of the gel against P. americana at high density were 0.208, 0.246, 0.361 and 0.466 g/m(2) on wood, cement, mud and thatch surfaces, whereas against B. germanica the values were 0.079, 0.081, 0.089 and 0.055 g/m(2) respectively, indicating a significantly (P<0.001) higher efficacy of Goliath gel against B. germanica than P. americana. The results of fitting logistic regression model to the observed percentage mortality with log dose and cockroach density as explanatory variables satisfactorily described the observations at all densities on each surface. The pattern of response to increasing dosages was similar for all the three density levels on each of the surfaces in P. americana and B. germanica. INTERPRETATION & CONCLUSION The effectiveness assessed against P. americana and B. germanica using logistic regression model suggested that the gel when applied at the appropriate dosages on wood, cement, mud and thatch surfaces could cause >80 per cent mortality of these species in dwellings having these types of surfaces.