Community-level responses by stream insects to neem products containing azadirachtin

Outdoor stream channels were treated with a commercial neem formulation, Neemix(R) 4.5, and a neem extract (no formulation ingredients) to determine the effects on aquatic insect communities. An exposure period of 5 h was chosen to simulate the transient nature of pesticide residues in streams and rivers after aerial applications. Multivariate analytic procedures based on Bray-Curtis similarity matrices were used to compare community structure among the replicate channels 9 d after treatment. No significant differences in community structure were found among controls and channels treated with Neemix at an azadirachtin concentration of 0.28 mg/L, but a multivariate measure of community stress indicated an increase in variability among treated channels. Significant differences in community structure were found among controls and channels treated with Neemix at 0.84 and 2.54 mg/L, and this resulted from reductions in several hey taxa. During subsequent experiments with a neem pow der extract. the formulation ingredients of Neemix were at least partially responsible for the significant effects on community structure at 0.84 mg/L azadirachtin. No significant differences were found among controls and channels treated with the extract at 0.9 mg/L, whereas the community structure of aquatic insects in channels treated at 3.0 mg/L differed significantly from controls. In a Canadian forest pest-management contest, the expected environmental concentration in water bodies of areas sprayed with azadirachtin at 50 g/ha is 0.035 mg/L.