Comparison of six artificial diets for western corn rootworm bioassays and rearing

Authors: MEIHLS, LISA - Evogene; HUYNH, MAN - University Of Missouri; LUDWICK, DALTON - University Of Missouri; Coudron, Thomas; French, Bryan; Shelby, Kent; HITCHON, ANDREA - University Of Guelph; SMITH, JOCELYN - University Of Guelph; SCHAAFSMA, ART - University Of Guelph; Pereira, Adriano; Hibbard, Bruce

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2018
Publication Date: 9/5/2018
Citation: Meihls, L., Huynh, M.P., Ludwick, D.C., Coudron, T.A., French, B.W., Shelby, K., Hitchon, A.J., Smith, J.L., Schaafsma, A.W., Pereira, A.E., Hibbard, B.E. 2018. Comparison of six artificial diets for western corn rootworm bioassays and rearing. Journal of Economic Entomology. 111(6):2727-2733. https://doi.org/10.1093/jee/toy268.
DOI: https://doi.org/10.1093/jee/toy268

Interpretive Summary: The western corn rootworm (WCR) is one of the most destructive pests in the U.S. Corn Belt. Transgenic maize expressing Bt toxins have been widely adopted as a management strategy. However, resistance to Bt toxins targeting WCR has already occurred. To investigate the mechanisms of resistance, we utilized genetic sequencing technology on newly hatched resistant and susceptible WCR larvae which had fed on seedling maize with and without a Bt toxin. In a parallel experiment, only the midguts of neonate WCR from the same treatments were evaluated versus the whole larvae. Results documented that resistant WCR expressed a small, specific suite of up and down-regulated genes following feeding on Bt maize when compared to feeding the same maize without Bt. In contrast, susceptible WCR neonates expressed a very wide range of genes in response to feeding on Bt maize when compared to feeding on the same maize without Bt. Differentially expressed genes between susceptible and resistant WCR midgut revealed genes associated with cell membrane, immune response, detoxification, and potential Bt receptors which are likely related to Bt resistance. This research provides a framework to study the toxicology of Bt toxins and a potential mechanism of resistance to Bt in WCR.

Technical Abstract: The western corn rootworm, Diabrotica virgifera virgifera LeConte, is considered the most important maize (Zea mays L.) pest in the U. S. Corn Belt. Bioassays testing susceptibility to Bacillus thuringiensis Berliner (Bt) and other toxins to corn rootworm larvae often rely on artificial diet. Successful bioassays on artificial diet for corn rootworm can be challenging because of contamination. Toward the long-term goal of developing a universal artificial diet for western corn rootworm larvae, we compared larval survival, dry weight, and percentage of molt in 10-day bioassays from all current diets of which we were aware. In addition, as part of longer-term rearing efforts we recorded molting over an extended period (60 d). Six different artificial diets, including four proprietary industry diets (A, B, C, & D), the first published artificial diet for western corn rootworm, and a new diet (WCRMO-1) were evaluated. Western corn rootworm larval survival was above 90% and contamination was 0% on all diets for 10 d. Diet D resulted in the greatest dry weight and percentage molting when compared to the other diets. Although fourth instar western corn rootworm larvae have not been found previously, as many as 10% of the larvae from Diet B molted into a fourth instar prior to pupating. Overall, significant differences were found among artificial diets currently used to screen western corn rootworm for susceptibility and resistance to different Bt toxins. In order for data from differing Bt toxins to be compared, a single, reliable and high quality western corn rootworm artificial diet should eventually be chosen by industry, academia, and the public as a standard for bioassays.