Characterization of thermal and time exposure to improve artificial diet for western corn rootworm larvae

Authors: HUYNH, MAN - University Of Missouri; PEREIRA, ADRIANO - University Of Missouri; GEISERT, RYAN - University Of Missouri; VELLA, MIKE - Frontier Scientific; COUDRON, THOMAS - Retired ARS Employee; Shelby, Kent; Hibbard, Bruce

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2021
Publication Date: 9/1/2021
Citation: Huynh, M.P., Pereira, A.E., Geisert, R.W., Vella, M., Coudron, T.A., Shelby, K., Hibbard, B.E. 2021. Characterization of thermal and time exposure to improve artificial diet for western corn rootworm larvae. Insects. 12(9). Article 783. https://doi.org/10.3390/insects12090783.
DOI: https://doi.org/10.3390/insects12090783

Interpretive Summary: The western corn rootworm is the most serious pest of corn in the U.S. Corn Belt. This highly adaptive pest has evaded nearly all management tactics developed to date. Diet assays, whereby insects are exposed to toxins on artificial diet, are a critical component of resistance monitoring programs and evaluating new toxins. Published rootworm diets contain antibiotics that reduce bacterial contamination. But antibiotic ingestion necessarily alters the rootworm gut microbiota, and this change the outcome of toxin bioassays. Rapid heating, or Pasteurization, is one of the most widely applied techniques to reduce microbial contamination, and this could elimination of antibiotics from the mix. We characterized the effects of timed intervals of thermal exposure on the quality of rootworm diet by measuring larval weight, molting and survival. Our results indicated that temperatures had non-linear effects on performance of diet, but no impacts were observed on the exposure intervals evaluated. The optimum temperature of diet processing was 60°C for a duration less than 30 min. Significant losses in nutrients needed for rootworm growth and development in diet were observed when the diet was heated above 75°C even for brief durations caused a two-fold reduction in larval weight gain, and delays in larval molting. These findings will guide the continued development of commercially available, sterilized rootworm diets, and will also provide insights into the design of diets for other insects.

Technical Abstract: The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is the most serious pest of maize (Zea mays L.) in the U.S. Corn Belt. This highly adaptive pest has evaded nearly all management tactics developed for managing it. Diet assays, whereby insects are exposed to toxins on artificial diet, are a critical component of resistance monitoring programs and evaluating new toxins. Published WCR diets (e.g., WCRMO-2) contain antibiotics to alleviate bacterial contamination. However, ingestion of antibiotics likely results in changes in WCR gut microbiota, and may cloud determination of WCR susceptibility to toxins. In diet processing, heating is one of the most widely techniques to alleviate microbial contamination and this can often enable elimination of antibiotics. Toward the goal of developing a diet free antibiotics for WCR, we characterized the effects of thermal exposure (50 °C - 141 °C) and time of thermal exposure on quality of WCRMO-2 diet based on life history parameters of larvae (weight, molting and survival) reared on WCRMO-2 diet. Our results indicated that temperatures had non-linear effects on performance of WCRMO-2 diet, and no impacts was observed on the time exposure evaluated. The optimum temperature of diet processing was 60 °C for duration less than 30 min. Significant losses in nutrients needed for WCR growth and development in WCRMO-2 diet were observed when the diet was heated over 75 °C. Additionally, exposing WCRMO-2 diet to high temperatures (110 °C - 141 °C) even if constrained for brief duration (0.9 - 2.3 s) caused 2-fold reduction in larval weight, and significant delays in larval molting, but no difference in survival for 10 days compared with the control diet made at temperature of 65 °C for 10 min. Our findings might provide insights into thermal exposure and duration of exposure in insect diet processing.