Baseline dose-responses of lesser mealworm, Alphitobius diaperinus (Coleoptera: Tenebrionidae) to insect growth regulators

The cancellation of most organophosphate and carbamate insecticides and the emerging resistance to currently available insecticides in the lesser mealworm, Alphitobius diaperinus (Panzer), necessitate the research towards novel alternative compounds.Baseline dose-response bioassays were conducted with three different types of insect growth regulators (IGR’s) including juvenile hormone analog (fenoxycarb), chitin synthesis inhibitor (diflubenzuron), and the ecdysone agonist (20-hydroxyecdysone) on 1st-and-8th larval instars, 2-d old pupae, and 1-wk old adult beetles. Beetles were exposed to a range of concentrations through topical application, tarsal contact with treated wood shavings, and feeding on treated chicken feed that simulate the possible ways of insecticidal absorption by beetles in poultry facilities. Each beetle was observed weekly to estimate percentage mortality and abnormal growth for each treatment. Topically applied diflubenzuron killed more than 80% of treated 8th instar larvae at all the concentrations and was also very effective on topically treated pupae.The diflubenzuron and 20-hydroxyecdysone treated diet was more effective against 1st instar larvae as compared to 8th larval instar and adults. 1st-and-8th larval instars exposed to fenoxycarb treated diet were heavier and had a prolonged larval period. These larvae failed to pupate and died in a larval-pupal intermediate stage. Fenoxycarb was the most effective among all IGR’s tested against 8th instar larvae when applied on wood shavings. Fenoxycarb was very effective against topically treated 8th instar larvae and pupae. I will discuss the potential of fenoxycarb and diflubenzuron for lesser mealworm management.