Effects of SmartStax and SmartStax PRO maize on western corn rootworm larval feeding injury and adult life history traits

Western corn rootworm (WCR; Diabrotica virgifera virgifera LeConte) field-evolved resistance to maize expressing proteins derived from Bacillus thuringiensis (Bt) has created management challenges for growers across the United States (U.S.) Corn Belt. Growers cultivate pyramided hybrids expressing two Bt proteins, such as SmartStax, to mitigate resistance; however, decreased efficacy of rootworm-Bt pyramids has been documented in local areas of the Corn Belt. SmartStax PRO, the most recent rootworm-active technology registered in the U.S., contains a new DvSnf7 dsRNA construct targeting the WCR. This study characterized the efficacy of non-rootworm Bt, SmartStax, and SmartStax PRO maize in fields with known Bt-susceptible and Bt-resistant WCR populations. Mating pairs of Bt-susceptible and Bt-resistant WCR were established to identify differences in life history parameters after feeding on SmartStax or SmartStax PRO ear tissue.
SmartStax and SmartStax PRO provided excellent root protection against Bt-susceptible WCR. Both transgenic hybrids significantly reduced root injury compared to non-rootworm Bt maize and SmartStax PRO provided the greatest root protection in two maize fields with Bt-resistant WCR. Egg production of Bt-susceptible and Bt-resistant WCR was significantly higher on non-rootworm Bt maize compared to SmartStax or SmartStax PRO. Bt-susceptible female WCR laid significantly fewer eggs after feeding on either SmartStax or SmartStax PRO compared to Bt-resistant WCR. Mean head capsule width and egg viability were not significantly different between populations or among treatments. Collectively, results suggest that SmartStax PRO may significantly reduce root injury in areas of Bt resistance while also decreasing the egg production of WCR females within individual cornfields.