Across the corn belt depending on time of year | Rootworm resistance to RW-Bt traits have been documented for many years, starting in 2009 with the single event YieldGard-RW which is Cry3Bb1.
Resistance to Dow Herculex (Cry 34-35) was documented in 2013.
Resistance to Syngenta mCry3A was documented in 2011. Durcade consists of two Cry 3 toxins (mCry3A + eCry3.1Ab). When introduced in 2014, resistance was already documented for one of the components (2011) so the second component failed quickly with resistance documented 2 years after introduction (2016).
SmartStak is simply a combination of YieldGard-RW (Cry 3Bb1) and Herculex (Cry 34/35) to which the single events had resistance documented so it is no surprise that resistance to the combination was documented in 2017.
Qrome was introduced in 2014 and consists of mCry3A (resistance documented in 2011) + Herculex (cry 34/35) (resistance documented in 2013), so of course, Qrome failures were to follow quickly.
SmartStak Pro is SmartStak toxins + Plus RNAi. The logic in this pyramid was the Bt toxins would prevent root feeding while the RNAi toxin killed them. However, when introduced, the Bt toxins were already burned out and ineffective, leaving the RNAi as a single toxin which rootworm will quickly become resistant to. Laboratory studied (published in 2018) showed resistance in rootworm occurred in 2 generations. This is compared to 3-7 generations in the lab to generate Bt resistance.
Pioneer Vorceed is exactly the same RNAi as SmartStak Pro (cross licensed) and will follow the same course to resistance as SmartStak Pro.
RNAi is already failing in Iowa. I posted some pictures earlier and the beneficial impact of biocontrol nematodes (an independent mortality factor) with the failing trait.
The role of Biocontrol Nematodes is to attack the resistant rootworm survivors and extend the durability of the trait. Even if the trait is suffering economic root feeding, it is still killing a lot of rootworms. Biocontrol nematodes move in and attack the survivors of the toxin. |
rootworm damage on CRW corn paid for by seed companies
