Effect of an Azadirachtin Formulation on Six Nontarget Aquatic Macroinvertebrates

Effects of a botanical pesticide, azadirachtin, were evaluated on nontarget aquatic macroinvertebrates found in SW Montana. A neem product formulated for commercial use and its petroleum-based, inert carrier alone were used to test the hypothesis that a commercial, U.S. Environmental Protection Agency-approved formulation of the pesticide, azadirachtin-A, derived fromextractsofneemtreeseeds, Azadirachtaindica A.Juss.(Family:Meliaceae),istoxictonontarget aquatic macroinvertebrates in Montana river systems. LC50s (24 h) for 5 insect species, Drunella grandis (McDunnough), Drunella doddsi (Needham), Skwala parallela (Frison), Brachycentrus occidentalis Banks, and Brachycentrus americanus (Banks), and 1 isopod species, Caecidotea inter- media (Forbes) varied from 1.8 to 9.2 ppm of the full formulation. The full formulation consisted of: azadirachtin (3% wt:wt); other neem-extracted material (32% wt:wt); petroleum solvents (65% wt:wt). LT50s for 4 ppm of this formulation were 9.4 to 748 hours for these field-collected macro- invertebrates. Without azadirachtin, but with the petroleum-based carrier, LT50s were 13.6-46.7 h. These bioassays conducted late in winter and early spring of 1994 and 1995 and late summer and early fall of 1994 indicated mortality from the neem formulation was similar to herbicides 2,4-D and picloram, but mortality could be accounted for by action of petroleum solvents in the inert materials. This suggests the registration process of new pesticides should also include documented potential toxicity of inert components in the formulation to non-target aquatic insects.