Field and laboratory tests on the effects of cyhalothrin on adults of<i>Apis mellifera, Megachile rotundata</i>and<i>Nomia melanderi</i>

Abstract

SUMMARYThe toxicity of cyhalothrin to adults tended to be least to the alkali bee Nomia melanderi (LD50 = 0.036 μg/bee), intermediate to the honey bee (Apis mellifera) (0.022 μg/bee) and greatest to the alfalfa leafcutter bee (Megachile rotundata) (0.002 μg/bee), both in topical tests and in residue tests. Adding an adjuvant to cyhalothrin sprays changed the toxicity of cyhalothrin to bees in residue bioassay studies with varying results with adjuvant and species of bee. Cyhalothrin at as little as 2 ppm in syrup feeders caused a reduction in honey bee visitation. Spraying cyhalothrin at 0.028 kg a.i/ha on flowering alfalfa resulted in significant reductions in populations of alfalfa leafcutter bees at nesting blocks.