Toxicity of delta-phenothrin and resmethrin to non-target insects.

Background: The susceptibility of adult house cricket, Acheta domesticus (L.), adult convergent lady beetle, Hippodamia convergens (Guérin-Méneville), and larval fall armyworm, Spodoptera frugiperda (JE Smith), to resmethrin and delta-phenothrin synergized with piperonyl butoxide (PBO) was evaluated in a laboratory bioassay procedure.

Results: The 1 day LC(50) values for resmethrin + PBO were 23.2, 32.08 and 307.18 ng cm(-2) for A. domesticus, H. convergens and S. frugiperda respectively. The 1 day LC(50) values for delta-phenothrin + PBO were 26.9, 74.91 and 228.57 ng cm(-2) for A. domesticus, H. convergens and S. frugiperda respectively. The regression relationship between species mortality and concentration explained 51-81% of the variation for resmethrin + PBO and 72-97% of the variation for delta-phenothrin + PBO. The LC(50) values decreased with time for these insecticides for all surrogate species. In terms of sensitivities among the insects to resmethrin + PBO and delta-phenothrin + PBO, A. domesticus was most sensitive, followed by H. convergens and then S. frugiperda.

Conclusion: The results indicate that resmethrin + PBO was generally more toxic than delta-phenothrin + PBO. Based on the results, A. domesticus seems to be a good surrogate species for estimating potential non-target terrestrial insect impacts from exposure to pyrethroids used in public health applications.