Bacillus thuringiensis is a Gram-positive sporulating bacterium that produces large amounts of sporulation specific proteins. These proteins accumulate as parasporal inclusions and are protoxins with selective activity for insect larvae. Generally, the inclusion is deposited outside the exosporium and is released into the environment separately from the spore. In subspecies finitimus, however, the inclusion and the spore share the common exosporium and are released together. The exosporium is more hydrophobic than the spore (Koshikawa et al., 1989), and exosporium enclosed inclusions are expected to be more hydrophobic than free inclusions. The availability of protoxins to susceptible larvae may be dependent upon the hydrophobicity of the inclusions. Subspecies israelensis produces inclusions composed of protoxins active on mosquito larvae. The inclusions of israelensis are released separately from the spore and are probably hydrophilic and not readily available to these larvae in nature. If the inclusions of israelensis were enclosed within the exosporium, then the protoxin should be more accessible and thus a more effective biological control agent. The aims of the preliminary planning study are to determine the effects of the exosporium on the hydrophobicity of parasporal inclusions, and to determine the feasibility of engineering, by genetic techniques, the protoxin of israelensis inside an exosporium. %%% This is a planning study to determine the feasibility of developing a biological insecticide effective against mosquito larvae. The approach is to take advantage of natural antilarval proteins produced by a bacterium in the course of sporulation. Mosquito- borne diseases of man and other animals represent an extremely significant world health and economic problem, particularly in the third world; one alone, malaria, is the number one cause of childhood mortality in the world. Chemical insecticides are not only unattractive because of their toxicity to animals and the environment, but they are becoming less and less effective as insects increasingly develop resistance to them. This research on biological pest control is therefore of great significance to both human health and the environment.
