Biolarvicides, based on mosquitocidal toxins of certain strains of Bacillus sphaericus and Bacillusthuringiensis var israelensis H-14 (Bti) are highly effective against mosquito larvae at very lowdoses and safe to other non-target organisms. During past two decades various biolarvicide formulationsproduced in India and abroad have been tested at Malaria Research Centre and some formulationshave undergone large-scale operational trials. Biolarvicide formulations of B. sphaericusare useful in the control of Culex and certain Anopheles spp, such as An. stephensi and An. subpictus,but not much effective against An. culicifacies and almost ineffective against Aedes aegypti.Repeated application of B. sphaericus in the same habitat, however, results in the developmentof resistance in larvae of target mosquitoes. In view of its low specificity for An. culicifacies andthe potential for resistance in An. stephensi, B. sphaericus has limited prospects for control of malariavectors. However, with some resistance management, B. sphaericus can still be used againstCulex mosquitoes. On the other hand Bti formulations, which have broader spectrum of activityagainst Aedes, Culex and Anopheles spp, have not shown significant development of resistance inmosquitoes but their activity in field, particularly against surface feeding anopheline larvae is affectedby various bioenvironmental factors, thus requiring weekly application in most habitats. Toovercome this problem development of slow release formulations and genetically engineered biolarvicidesby transplanting mosquitocidal toxin genes of Bti and B. sphaericus in some other environmentallycompatible organisms have been investigated by different scientists
