Assessing artificial diet and susceptibility of Mexican corn rootworm (Diabrotica virgifera zeae Krysan & Smith) larvae to Gpp34Ab1/Tpp35Ab1 protein

Mexican corn rootworm, Diabrotica virgifera zeae (Krysan & Smith), and western corn rootworm, D. v. virgifera LeConte, are both subspecies of D. virgifera . Knowledge of Mexican corn rootworm is extremely limited and biological and management assumptions for it, including resistance management programs, are based on western corn rootworm. To better understand the degree of similarity to western corn rootworm and potential management options, Mexican corn rootworm from a Texas field population were exposed to different transgenic corn hybrids, reared on an artificial diet designed for western corn rootworm, and tested for their response to varying doses of Gpp34Ab1/Tpp35Ab1. The results of the field test revealed corn hybrids that contained a single Cry protein were less protected than hybrids expressing two or more proteins with the most protection provided by a hybrid expressing two Cry toxins and a double-stranded RNA (dvSnf7). Mexican corn rootworm larvae grew normally on the artificial diet, though they ultimately weighed less when compared to western corn rootworm larvae. Lastly, Mexican corn rootworm larvae from this population were significantly less susceptible to Gpp34Ab1/Tpp35Ab1 than a susceptible western corn rootworm colony, but the insects responded similarly in terms of weight inhibition. Together, the field and diet toxicity data suggest that the Texas field population of Mexican corn rootworm was tolerant to Gpp34Ab1/Tpp35Ab1 and likely the other Cry proteins designed to control corn rootworms. Currently, fields with similar issues to this situation should incorporate a pyramided corn hybrid expressing dsRNA and Bt proteins. • Diet formulated for western corn rootworm ( Diabrotica virgifera virgifera LeConte) can be used to evaluate Mexican corn rootworm ( D. v. zeae Krysan & Smith) in diet toxicity assays. • Mexican corn rootworm eggs can successfully be retrieved from field-collected adults using methods established for western corn rootworm thereby enabling research on this understudied insect. • Incomplete resistance or increased tolerance to Gpp34Ab1/Tpp35Ab1 may be occurring in at least one population of Mexican corn rootworm from Texas.