Published May 1993
This review concerns the oldest microbial insecticide currently in commercial use -- Bacillus thuringiensis (Bt), which contains the insecticidal active d-endotoxin. Bt insecti cides, which are toxic for larvae of lepidoptera, can be used effectively on fruits, vegetables, rice, ornamentals, lawns, forests, shade trees, and tobacco against bagworm, cabbage looper, gypsy moth, diamond back moth, and other leaf-eating caterpillars. A subspecie, Btvar. israelensis, for instance, is especially effective against mosquito and black fly larvae.
Bt insecticides are highly specific, biodegradable, and nonaccumulative. Their applications offer little risk of long-term impact on the ecosystem and contamination of the environment, and insects do not tend to develop resistance to the microorganism as easily as to chemical insecticides. But they must be ingested to be effective, generally act slower than chemical insecticides, and their viability can be affected by weathering and sunlight after application.
Bt insecticides are produced commercially by submerged aerobic fermentation at about 305C (865F) and atmospheric or near atmospheric pressure under sterile conditions in a medium containing energy sources, which are normally carbohydrates such as mo lasses; nitrogen sources, which can be compounds such as cottonseed meal or flour and corn steep liquor; and a minor or trace amount of other ingredients such as vitamins and minerals. From data presented in a patent, we have prepared an economic estimate for the production of a Bt concentrate containing diatomite at 2 million lb/yr (910 t/yr).
