[Effect of Bacillus thuringiensis var. israelensis (Bti) on detoxification enzyme activity of larvae of Culex pipiens pallens and Aedes aegypti].

OBJECTIVE: To investigate the effect of Bacillus thuringiensis var. israelensis (Bti) on the activities of three detoxification enzymes of Culex pipiens pallens and Aedes aegypti larvae. METHODS: The activities of glutathione transferase, acetyl cholinesterase and carboxyl esterase, were detected after two kinds of mosquito larvae were treated by Bti at different time and concentrations. RESULTS: The activities of three detoxification enzymes of the two kinds of mosquito larvae were influenced by Bti treatment. The activity of glutathione transferase was increased after the Bti treatment, but declined significantly and inhibited at a low level sustainably. The activity of carboxyl esterase was increased after the Bti treatment, but recovered to normal level quickly. Acetyl cholinesterase was affected slightly by the Bti treatment, shortly inhibited in the first time and then recovered. The active effects of the three detoxification enzymes were positively related to the concentration of Bti. CONCLUSION: The enzyme activities of glutathione transferase, acetyl cholinesterase and carboxyl esterase could be affected by Bti significantly.

[Characterization of Bacillus thuringrensis var. israelesis larvicide granules to larvae of mosquitoes].

OBJECTIVE: To develop a new formulation of Bacillus thuringrensis var. israelesis (Bti) granules and assess its effect on mosquito control. METHODS: The Bti granule formulation was produced by coating Bti liquid on the surface of the carrier. and imitation tests, persistence tests and field tests were carried to assess its mosquito larvicidal effect, extended period and stability. RESULTS: A strain of Bti isolated from field had high toxicity to mosquito larvae and its LC50 values for larvae of Culex pipiens pallens and Aedes aegypti were 0.461 0 microl/L and 1.713 3 microl/L respectively. The developed 216 ITU/mg Bti granules had a control effect of 83.3%-100% to larvae of C. pipiens pallens at the dosage of 1-3 g/m2, and 72.7%-100% to A. aegypti at the dosage of 3-5 g/m2. When the 3rd instar larvae of C. pipiens pallens were put in the water that was treated with the granules at the dosage of 0.5 g/m2 13 days before, the larval mortality still reached to 55.3%. The field tests showed that with the treatment of 2-4 g/m2 Bti granules, the control effects on the larvae were high from 92.4% to 100% within the first 3 days and about 51.6%-75.7% after 20 days. CONCLUSION: The developed new formulation of Bti granules with the isolated strain has a preferable control effect on mosquito larvae and reveals a longer persistence and better stability than liquid formulation in the field tests.