This study shows that drug resistant strains are able to transfer genes encoding drug resistance.

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A formulation was developed from the metabolite(s) of a novel Pseudomonas fluorescens Migula strain (VCRC B426) and tested against 4th-instar larvae and pupae of three species of vector mosquitoes, Anopheles stephensi Liston, Culex quinquefasciatus Say and Aedes aegypti (L). The larvae and pupae of An stephensi were the most susceptible to the formulation, followed by those of C quinquefasciatus and Ae aegypti, in that order, and the dosage requirement for pupal mortality was less than that required for larval mortality. The LC 50 dosage requirements for larvae of these mosquito species were, respectively, 70.4, 511.5 and 757.3 mg protein ml À1 , whereas for pupae they were, respectively, 2.0, 9.4 and 19.2 mg protein ml À1 . The lethal fraction was purified from the culture broth and its molecular mass, as determined by high performance liquid chromatography, was 44 kDa. This is the first report of a microbial formulation acting upon mosquito pupae, a non-feeding stage. Its mode of action and efficacy to control mosquitoes under field conditions need to be studied further.

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