Acute toxicity of insecticides to Micromus tasmaniae (Neuroptera: Hemerobiidae) and Chrysoperla carnea (Neuroptera: Chrysopidae): LC50 and LC90 estimates for various test durations

The acute toxicities of 6 insecticides deriving from 5 different insecticide classes were assessed in laboratory tests with Micromus tasmaniae (Walker) after different post treatment periods (1.5-360 h). The aim was to determine optimal test durations for the calculation of stable (i.e., no further change over time) LC50 and LC90 estimates. In addition, the responses of M. tasmaniae to the above insecticides were compared with those for Chrysoperla carnea (Stephens). In short-term evaluations (less than or equal to 24 h), methyl-parathion caused the highest mortality in M. tasmaniae. The toxicity of methyl-parathion did not change significantly over time; however, the toxicity of azinphos-methyl, cypermethrin, fenoxycarb, and diflubenzuron did. Minimum posttreatment periods of 48, 72, 120, and 360 h were necessary before stable lethal concentrations estimates could be determined for azinphos-methyl, cypermethrin, fenoxycarb, and diflubenzuron, respectively. At the point of stable LC50s and LC90s, the latter compounds were more toxic to M. tasmaniae than methyl-parathion. Tebufenozide did not cause any mortality in either lacewing species. Comparisons between the 2 lacewings species showed that M. tasmaniae was more sensitive to methyl-parathion, azinphos-methyl, and cypermethrin than C. carnea, whereas the toxicity of fenoxycarb and diflubenzuron was similar to both species. The results demonstrate the importance of carrying out acute toxicity studies to an adequate posttreatment period to avoid underestimating the toxicities of insecticides. In addition, the comparisons with C. carnea demonstrated that the results of toxicity studies cannot be extrapolated to closely related families