Optimization of an artificial diet for western corn rootworm, Diabrotica virgifera virgifera, bioassays

The western corn rootworm (WCR) is the most serious insect pest of corn in the United States. An artificial diet for rearing WCR was originally derived from the diet for southern corn rootworm. Currently, several versions of a modified southern corn rootworm diet are used by industry and researchers for bioassays when monitoring for resistance and for screening for active substances. However, diet parameters such as texture, presentation, stimulants, pH and antimicrobials have not been fully investigated to optimize insect performance. To expedite screening of diet ingredients, mixture designs based on the Scheffé polynomial were used. WCR populations were evaluated on all diets simultaneously to enable direct comparisons between proprietary industry diets and our own formulations. Criteria for comparison included the diet’s suitability for assay use (i.e., levels of contamination, larval survival, development and weight, and assay duration). The first round of diet optimization, where eight components were varied, resulted in 22 unique diet formulations. One of these had larval performance similar to one of four proprietary industry diets. The second round of diet optimization consisted of a four-component mixture design with 21 unique diet formulations. Optimization based on results from this design resulted in a formulation with larval performance greater than three of four proprietary industry diets. In addition, the second round of independent diet formulation optimization indicated that a major component, corn root tissue, had a positive effect on development of WCR. Significant improvements in larval survival, weight gain, and development relative to previous diets were accomplished within two rounds of diet optimization.