Effects of SmartStax(& REG;) and SmartStax(& REG;) PRO maize on western corn rootworm (Diabrotica virgifera virgifera LeConte) larval feeding injury and adult life history parameters

Field-evolved resistance of the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, to Bacillus thuringiensis Berliner (Bt) proteins Cry3Bb1 and Cry34/35Ab1 (now classified as Gpp34Ab1/Tpp35Ab1) expressed in the pyramid SmartStax(& REG;) has been documented in areas of the United States (U.S.) Corn Belt. SmartStax(& REG;) PRO is a recently registered rootworm-active pyramid containing the same Bt proteins expressed in SmartStax(& REG;) plus DvSnf7 dsRNA. Little to no published data is available comparing efficacy of the technologies or potential effects of dietary exposure on adult WCR fitness. Therefore, experiments were conducted to compare effects of adult WCR dietary exposure to SmartStax(& REG;) and SmartStax(& REG;) PRO on life history parameters and efficacy of the technologies in the field with both Bt-susceptible and Bt-resistant WCR populations. WCR life history parameters evaluated included adult longevity, head capsule width, egg production, and egg viability. Results of small-plot field trials indicated that both technologies provided a high level of root protection when a Bt-susceptible WCR population was present. Root protection was reduced on SmartStax(& REG;) but maintained on SmartStax(& REG;) PRO when WCR Bt resistance occurred. Lifetime egg production was the key life history parameter that was significantly reduced when either Bt-susceptible or Bt-resistant adult WCR were fed SmartStax(& REG;) or SmartStax(& REG;) PRO diet. A potential fitness advantage was apparent as egg production was significantly higher in the Bt-resistant than Bt-susceptible population. The similar response by the Bt-susceptible WCR population to SmartStax(& REG;) and SmartStax(& REG;) PRO indicates that results were caused by sublethal dietary exposure to Bt proteins. Adult size (males < females) and egg viability (high: >95%) were not significantly different among treatments but longevity results were inconsistent between years. Collectively, the field efficacy and life history parameter data expand existing knowledge of SmartStax(& REG;) and SmartStax(& REG;) PRO technologies, which will inform practical WCR resistance management programs.

Automated summary

Field-evolved resistance of western corn rootworm to Bt proteins in SmartStax has been documented, but little is known about the effects on adult rootworm fitness. This study compared the effects of dietary exposure to SmartStax and SmartStax PRO on life history parameters and efficacy in the field. Results showed that both technologies provided high root protection against susceptible rootworm populations, but protection was reduced on SmartStax PRO when resistance occurred. Egg production was significantly reduced in both susceptible and resistant populations fed SmartStax or SmartStax PRO. The findings expand our knowledge of these technologies and can inform resistance management programs.