## 4 Field Efficacy of RNAi for Insect Control, Insect Resistance Management, and RNAi Resistance  
### Field Efficacy of RNAi Traits  
The U.S. EPA approved the first RNAi product for insect control in 2017 [146], representing the first new MOA for WCR control since the release of the Cry34 Ab1/Cry35 Ab1 binary protein in 2005 [147]. As previously indicated, this product (SmartStax(r) PRO) expresses three rootworm-active \(Bt\) proteins, Cry3 Bb1 and Cry34 Ab1/Cry35 Ab1, as well as _DvSnf7_ dsRNA [33]. SmartStax(r) PRO also contains three Lepidopteran-active \(Bt\) proteins (Cry1A.105/Cry2 Ab2 and Cry1F) and genes for glyphosate tolerance [33]. Given reports of field-evolved resistance to Cry3 Bb1 [21; 22; 23; 26; 30], an efficacy evaluation of this product on Cry3 Bb1-resistant insects and field populations was performed [148]. Additionally, _DvSnf7_ dsRNA concentration-response larval bioassays were conducted on artificial diet using field-derived populations, a susceptible laboratory population, and a Cry3 Bb1-resistant population. Lastly, greenhouse experiments evaluating beetle emergence from plants expressing each trait individually (i.e., Cry3 Bb1, Cry34 Ab1/Cry35 Ab1, and _DvSnf7_) and in combination were conducted. The Cry3 Bb1-resistant population exhibited a significant 2.7-fold decrease in susceptibility to _Dv5 nf7_ dsRNA compared to the Cry3 Bb1-susceptible population. However, the Cry3 Bb1-resistant population lowered susceptibility was similar to other WCR field populations in diet bioassays. Cry3 Bb1-resistant and susceptible colonies had similar WCR adult emergence from plants expressing _DvSnf7_ and Cry34 Ab1/Cry35 Ab1, and WCR adult emergence from plants expressing _DvSnf7_ and _DvSnf7_ + Cry3 Bb1 was not significantly different when the Cry3 Bb1-resistant colony was evaluated [148]. Collectively, diet assay and _in planta_ experiments have demonstrated a lack of cross-resistance between Cry3 Bb1, Cry34 Ab1/Cry35 Ab1, and _DvSnf7_[148]. Previous research has also documented significant variation in susceptibility of WCR larvae from field populations to _DvSnf7_, with an LC\({}_{50}\) ranging from 4.07 to 40.51 ng/cm\({}^{2}\)[148]. This suggests that some populations might already exhibit higher tolerance to _DvSnf7_ dsRNA and resistance monitoring will be essential to track susceptibility changes in field populations to promote trait durability. Further field studies evaluated the efficacy of SmartStax(r) (Cry3 Bb1 + Cry34 Ab1/35 Ab1 pyramid) and SmartStax(r) PRO maize (also expresses _Dv5 nf7_ dsRNA) against western and northern corn rootworms [32]. Field trials conducted between 2013 and 2015 across the U.S. Corn Belt demonstrated that SmartStax(r) PRO could significantly reduce root damage ratings under high WCR larval densities, in areas of Cry3 Bb1 resistance, and in areas with greater than expected injury to Cry3 Bb1 or SmartStax(r). SmartStax(r) PRO also significantly reduced root damage ratings relative to SmartStax(r) in some field trials, indicating that _DvSnf7_ dsRNA can provide additional root protection when coupled with \(Bt\) proteins [32]. In addition to enhanced root protection, SmartStax(r) PRO also reduced adult emergence compared to SmartStax(r), single-event Cry3 Bb1 and Cry34 Ab1/Cry35 Ab1 hybrids, and the non-\(Bt\) control [32]. Collectively, the reduced root damage ratings and decreased adult emergence associated with SmartStax(r) PRO suggest that the addition of _DvSnf7_ and other RNAi traits could serve as a valuable tool for insect resistance management (IRM) strategies [32]. Various resistance modeling scenarios indicated that inclusion of _DvSnf7_ dsRNA could promote durability of the expressed \(Bt\) proteins and decrease the rate of resistance evolution relative to SmartStax(r), even in areas with suspected resistance to Cry3 Bb1 [32]. However, no work has been performed to evaluate the role of RNAi traits under scenarios with resistance to both Cry3 Bb1 and Cry34 Ab1/Cry35 Ab1.