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

Outdoor stream channels were treated with a commercial neem formulation, Ne emix(R) 4.5, and a neem extract (no formulation ingredients) to determine t he effects on aquatic insect communities. An exposure period of 5 h was cho sen to simulate the transient nature of pesticide residues in streams and r ivers after aerial applications. Multivariate analytic procedures based on Bray-Curtis similarity matrices were used to compare community structure am ong 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 me asure of community stress indicated an increase in variability among treate d 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 struc ture 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 co mmunity structure of aquatic insects in channels treated at 3.0 mg/L differ ed significantly from controls. In a Canadian forest pest-management contes t, the expected environmental concentration in water bodies of areas spraye d with azadirachtin at 50 g/ha is 0.035 mg/L.