To eat or not to eat: Preference and performance of corn earworm on soybean tissues

Helicoverpa zea (Boddie), corn earworm, can be the most damaging insect pest of many crops in the southern U.S., including soybeans.  Previous research shows that larvae feed on multiple soybean tissue types; however, knowledge regarding larval preference and performance in this system is scarce.  The objective of these studies was to identify larval feeding preferences and performance on different tissue types. I conducted no-choice and choice assays using early-second instar and late-fourth instar corn earworm larvae.  Colony raised larvae were placed on fresh tissue every two days and allowed to feed until pupation.  During feeding periods, survival rates, consumption indices and growth rates were calculated from changes in larval body mass and soybean tissue. In no-choice assays, early-instar larvae reached the pupal stage when fed on newly emerging trifoliates 31% of the time and on older leaf tissues 50% of the time; survival was poor on other tissue types, suggesting that early instar larva perform better when fed leaf tissue.  Late-instar larvae survival rates were 78%, 85%, and 85% for newly emerged leaves, fully emerged leaves, and fully developed seeds, respectively, suggesting better performance on leaves and developed pods. Early instar larvae preferred to feed on newly emerging trifoliates and early developing pods, with an average of 51% and 38% of tissues consumed, respectively. Late-instars did not show a significant tissue preference. Ultimately determining preference and performance of corn earworm on soybeans will help expand knowledge on herbivory choice, growth and fecundity to illuminate ecological interactions in this system.