EFFECTS OF BACILLUS-THURINGIENSIS VAR ISRAELENSIS ON NONTARGET BENTHIC ORGANISMS IN A LENTIC HABITAT AND FACTORS AFFECTING THE EFFICACY OF THE LARVICIDE
Cs. Charbonneau et al., EFFECTS OF BACILLUS-THURINGIENSIS VAR ISRAELENSIS ON NONTARGET BENTHIC ORGANISMS IN A LENTIC HABITAT AND FACTORS AFFECTING THE EFFICACY OF THE LARVICIDE, Environmental toxicology and chemistry, 13(2), 1994, pp. 267-279
Field and laboratory studies were conducted to determine the effects o
f Bacillus thuringiensis var. israelensis (Vectobac G(R)) on waterfowl
macroinvertebrate food resources at the Minnesota Valley National Wil
dlife Refuge,Bloomington, Minnesota. Laboratory toxicity tests were co
nducted to evaluate the influence of environmental variables (e.g., te
mperature and depth). The EC50 was 0.20 ppm for Chironomus riparius. F
ield studies evaluated the effects of three applications at 5.6 kg/ha
on benthic communities during the spring and summer of 1989, and three
experiments with one application of 5.6 kg/ha and 28.1 kg/ha during t
he spring and summer of 1990. Benthic invertebrates were sampled befor
e each application of Vectobac-G and at 48 h after application. There
was no reduction of the major taxa found in the ponds that could be ac
counted for by the treatments. However, results from laboratory toxici
ty tests conducted with field-collected Chironomidae indicated that th
ese organisms were affected at 5.6 and 28.1 kg/ha. Further toxicity te
sts using Chironomus riparius determined that various environmental va
riables influenced the efficacy of Vectobac-G, including temperature,
larval instar, water depth, and water surface area coverage by macroph
ytes. This study indicates that chironomids (a major waterfowl food so
urce) are adversely affected by Vectobac-G under a controlled laborato
ry situation; however, environmental factors reduce the efficacy of th
e larvicide in the field.