Neonicotinoids can cause arrested ecdysis in Coleoptera

Neonicotinoids are a widely utilized class of insecticides that bind to nicotinic acetylcholine receptors as their primary mode of action causing paralysis and death. Neonicotinoids have also been shown to affect various aspects of insect physiology and behavior. Studies were conducted in 3 coleopteran species to determine the effects of neonicotinoids on ecdysis. Neonicotinoids were topically applied to pupae of Tenebrio molitor Linnaeus, Tribolium castaneum Herbst, and Leptinotarsa decemlineata Say at doses that did not have direct paralytic effects. Topical neonicotinoid applications at least 1 d before adult emergence led to arrested ecdysis in all 3 beetle species. Adults developed beneath the pupal cuticle and initiated normal pre-ecdysis movements, including initiating shedding of the abdominal cuticle and tracheal linings. However, the process stalled at this stage; the remaining pupal cuticle and tracheae were not shed, wings remained unexpanded, and the head and thoracic ecdysial lines usually did not break. Despite these impairments, the adults remained alive, as indicated by movements of their antennae and legs. Topical application of neonicotinoids to last-instar larvae of T. molitor and L. decemlineata and penultimate instar of L. decemlineata also caused arrested pupal ecdysis and arrested larval ecdysis, respectively. Data obtained using 4 neonicotinoids suggests nicotinic acetylcholine receptors are involved in the regulation of coleopteran ecdysis. Combined with results of previous research demonstrating neonicotinoids cause arrested ecdysis in Lepidoptera, this suggests that neonicotinoids could be disrupting the function of crustacean cardioactive peptide producing neurons.