Effects of a meridic diet supplemented with cotton leaf tissue on bollworm fitness

Authors: Little, Nathan; Mullen, Regina; Elkins, Blake; Parys, Katherine; Allen, Clint

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2020
Publication Date: 9/25/2020
Citation: Little, N., Mullen, R.M., Elkins, B.H., Parys, K.A., Allen, K.C. 2020. Effects of a meridic diet supplemented with cotton leaf tissue on bollworm fitness. Southwestern Entomologist. 45(3):1-9. https://doi.org/10.3958/059.045.0302.
DOI: https://doi.org/10.3958/059.045.0302

Interpretive Summary: The bollworm is a major pest of cotton that is tolerant to many synthetic and transgenic insecticides. To assess this insect’s susceptibility to insecticides, they are regularly collected from wild and cultivated hosts, placed into cups containing a synthetic diet, and returned to the laboratory for testing. The progeny from the following generation are utilized in bioassays to estimate the insect’s susceptibility to an insecticide of interest. This study found that when neonate larvae were fed cotton leaf tissue during the first seven days of life, their overall fitness was improved as evidenced by higher pupal weights than those on synthetic diet alone. As one might expect, when insects are large and healthy, they tend to have higher levels of tolerance. This may affect susceptibility estimates for insects in the field. However, this increase in pupal weight from feeding on leaves came at a cost, higher mortality. This study indicated that additional research is needed to address nutritional deficiencies in synthetic diet and that these shortcomings could drastically impact our estimates of insect susceptibility to various insecticides if not addressed.

Technical Abstract: 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 used in bollworm rearing have been altered from their original nutrient composition and what implications this may have on insect fitness. Therefore, this study assessed notable shortcomings of a commonly used meridic diet by exposing bollworms to cotton leaf tissue for short periods during early development to determine its effect on larval and pupal survival and weights. Mean survival of larvae ranged from a low of 60% where bollworms were exposed to Bt cotton leaves for a period of 7 d to a high of 100% on meridic diet. Mean pupation ranged from 58% to 95%, which closely mimicked survival of larvae at 7 d. Insect larvae reared on meridic diet through 7 d were more fit relative to those exposed to cotton leaf tissue, having higher larval weights and survival than other treatments. Conversely, pupal weights of bollworms exposed to meridic diet for the same 7 d period tended to lag behind those that were exposed to cotton leaf tissue. However, any fitness benefits gained from rearing larvae on leaf tissue may be offset by increased mortality prior to the pupal stage. This experiment demonstrated that larval and pupal fitness are impacted by supplementing meridic diet with leaf tissue, but additional research is needed to further investigate these effects across multiple generations.