Acute toxicity and risk assessment of permethrin, naled, and dichlorvos to larval butterflies via ingestion of contaminated foliage

Three Florida native larval butterflies (Junonia coenia, Anartia jatrophae, Eumaeus atala) were used in the present study to determine the acute toxicity, hazard, and risk of a 24 h ingestion of leaves contaminated with the adult mosquito control insecticides permethrin, naled, and dichlorvos to late 4th and early 5th in-star caterpillars. Based on 24-h LD50s for ingestion, naled was more acutely toxic than permethrin and dichlorvos to caterpillars. Hazard quotients using the ratio of the highest doses and the 90th percentile doses from field measurements in host plant foliage following actual mosquito control applications to the toxicological benchmarks from laboratory toxicity tests indicate potential high acute hazard for naled compared to permethrin and dichlorvos. Based on probabilistic ecological risk methods, naled exposure doses in the environment also presented a higher acute risk to caterpillars than permethrin and dichlorvos. The acute toxicity laboratory results and ecological risk assessment are based only on dietary ingestion and single chemical doses. It does not include other typical exposure scenarios that may occur in the environment. It is thus plausible to state that the ecological risk assessment presented here underestimates the potential risks in the field to caterpillars. However, one assumption that is scientifically feasible and certainly real from the results - if the environmental exposure doses of mosquito control operations are similar or higher to those presented here in leaves from the field, after applications, there will likely be significant mortalities and other adverse effects on caterpillar populations.