Toxicity of Bacillus thuringiensis var. israelensis formulations, spinosad, and selected synthetic insecticides to Chironomus tepperi larvae.
Three Bacillus thuringiensis var. israelensis (BTi) formulations, the bacterial metabolite spinosad, and 7 synthetic insecticides were bioassayed against 4th instars of Chironomus tepperi, a serious pest of rice in southern Australia. The BTi formulations returned 48-h product median lethal concentration (LC50) values (25 < or = 1 degrees C) of between 0.59 mg/liter (VectoBac water-dispersible granule [WDG], 3,000 international toxic units [ITU]/mg) and 2.15 mg/liter (Teknar suspension concentrate [SC], 1,200 ITU/mg). When LC50 values were adjusted to reflect nominal ITU values of the 3 products, there was still substantial variation, with LC50 values ranging from 1,770 ITU/liter (VectoBac WDG) to 2,580 ITU/liter (Teknar SC). Aquabac SC (1,200 ITU/mg) showed intermediate activity. Differential activity between formulations may reflect faster settling rates in the more active formulations, which may be a beneficial characteristic when controlling benthic species such as C. tepperi. Spinosad (24-h LC50 = 28.9 microg active ingredient [AI]/liter) and the synthetic insecticides we evaluated were all substantially more active than BTi. The highest activity was shown by the neonicotinoid compounds thiacloprid, acetamiprid, and clothianidin, which all returned 24-h LC50 values between 1 and 3 microg AI/liter. Indoxacarb and thiomethoxam showed the lowest activity of the synthetic compounds evaluated.
Stevens
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MM
NSW Department of Primary Industries and Cooperative Research Centre for Sustainable Rice Production, Yanco Agricultural Institute, Australia.
Helliwell
S
S
Hughes
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PA
D000818:Animals; D001413:Bacillus thuringiensis; D001681:Biological Assay; D002683:Chironomidae; D004338:Drug Combinations; D007306:Insecticides; D007814:Larva; D018942:Macrolides; D010572:Pest Control, Biological
D004338:Drug Combinations; D007306:Insecticides; D018942:Macrolides; C415329:spinosad