Distribution and insecticide resistance of the plague flea Xenopsylla cheopis in Maharashtra State, India.

Distributions are reported for commensal rat fleas, predominantly Xenopsylla cheopis (Rothschild), in the State of Maharashtra, India, including the city of Bombay, during 1965-80. The X.cheopis flea index was high in most parts of Maharashtra, but low in Bombay. Rattus rattus Linnaeus is the principal host of X.cheopis, but the host range includes Bandicota bengalensis Gray, Golunda ellioti Gray, Mus musculus Linnaeus, Rattus blandfordi Thomas, R. norvegicus Berkenhout, Suncus caerulaeus Lerr, S. murinus Linnaeus and Tatera indica Hardwicke. X.cheopis was found to have high degrees of resistance to DDT, malathion and fenthion, tolerance to gamma HCH (= gamma BCH) but susceptibility to dieldrin. This insecticide resistance situation may contribute to the high flea indices prevailing in the state, with consequent risks of plague outbreaks. Two other species of rat flea, X.astia Rothschild and X.brasiliensis (Baker) were found to be less common than previously recorded. Their apparent replacement by X.cheopis is tentatively attributed, at least partly, to the selective advantage of insecticide resistance in the latter species.