Effects of a Meridic Diet Supplemented with Cotton Leaf Tissue on Bollworm Fitness

Rearing bollworm, Helicoverpa zea (Boddie), on synthetic diets for use in laboratory bioassays is a common practice around the world. Little is known about how insect diets currently utilized for bollworm rearing have been altered from their original nutrient composition and the implications this might have on insect fitness. Therefore, this study assessed notable shortcomings of a commonly used meridic diet by exposing bollworms to cotton (Gossypium hirsutum L) leaf tissue for short periods during early development to determine effect on larval and pupal survival and weights. Mean survival of larvae ranged from 60% when bollworms were exposed to Bt cotton leaves for 7 days to 100% on meridic diet. Mean pupation ranged from 58 to 97%, which closely mimicked survival of larvae at 7 days. Insect larvae reared on meridic diet through 7 days were fitter relative to those exposed to cotton leaf tissue, having greater larval weight and survival than other treatments. Conversely, pupal weight of bollworms exposed to meridic diet for the same 7-day period tended to lag behind those exposed to cotton leaf tissue. However, any fitness benefit gained from rearing larvae on leaf tissue might be offset by increased mortality before the pupal stage. The experiment demonstrated that larval and pupal fitness were impacted by supplementing meridic diet with leaf tissue, but additional research is needed to further investigate effects through multiple generations.