Comparison of insecticide toxicity in adult and larval stages of Spodoptera frugiperda (J.E. Smith) and Helicoverpa armigera (Hünber) (Lepidoptera: Noctuidae)

Abstract

Larvae of Helicoverpa armigera and Spodoptera frugiperda are important pests of agricultural commodities and while chemical control targeting larvae of these pest species is widely adopted, suppression of populations by bisexual attract-and-kill strategies which target adults also have potential applications in management. This study investigated the relative toxicity of insecticide groups registered as mixing partners for attract-and-kill agents in Australia. Contact and ingestion toxicity in adult and larval stages of H. armigera and S. frugiperda was tested by administering methomyl and spinosyn insecticides topically and orally in laboratory bioassays. Methomyl was generally the least toxic insecticide and larvae of both species were less sensitive to methomyl than adults. Adult mortality induced by methomyl was stable from 24 to 72 h after treatment in S. frugiperda whereas mortality of adult H. armigera increased from 24 to 72 h. Spinosyns were slower acting in both H. armigera and S. frugiperda with increases in adult mortality from 24 to 72 h after treatment. Spinetoram was the most toxic insecticide on adults and larvae both H. armigera and S. frugiperda with higher insecticidal activity on larvae compared to adults of both species. Spinosad was also more toxic on larvae of S. frugiperda compared to adults. This was in contrast to H. armigera larvae which were less sensitive to spinosad than their adult counterparts. A between-species comparison of insecticide toxicity showed larvae of both species were equally sensitive to spinosyns while adults of H. armigera were more sensitive to all three insecticides than adults of S. frugiperda. These results suggest that spinosyns could be effective options for strategies that target adult life stages of both H. armigera and S. frugiperda.