Effect of methoprene impregnated packaging on Tribolium castaneum and Trogoderma variabile egg-to-adult development

The insect growth regulator methoprene, is registered for treatment of empty storage facilities, stored grain, and packaging.  Methoprene adversely affects the number of eggs laid by female beetles, egg hatchability, and larval development.  The objective of this research was to evaluate normal adult emergence of Tribolium castaneum (Herbst) and Trogoderma variabile Ballion from eggs laid by adult beetles on the inside and outside surfaces of methoprene-treated packaging material at 27 and 32°C and 60% RH.  Inside and outside surfaces of methoprene-treated and untreated packages were cut into discs and fitted into 62 cm² Petri plates. The disc edges were glued down to deter larvae from crawling underneath the disc, and 500 mg of flour with yeast (T. castaneum) or vanilla shake mix (T. variabile) were added to the plates.  Ten mixed sex adults of a particular species were added to an individual disc, and adult T. castaneum were removed after 7 days and T. variabile were removed after 3 days.  Observations for normal adult emergence were made weekly, and emerged adults were removed from discs.  Results indicate a 100% supression of T. castaneum adult emergence on the outside and inside surfaces of the bagging material.  T. castaneum exposed to outside surfaces remained arrested in the larval stage, and those exposed to inside surfaces developed  as half pupae-half adult intermediates, irrespective of temperature.  T. variabile exposed to inside surfaces were unaffected by the methoprene-treated packages, and those exposed to outside surfaces normal adult emergence was reduced compared to the untreated control.