How well will stacked transgenic pest/herbicide resistances delay pests from evolving resistance?

Abstract

Resistance has evolved to single transgenic traits engineered into crops for arthropod and herbicide resistances, and can be expected to evolve to the more recently introduced pathogen resistances. Combining transgenes against the same target pest is being promoted as the solution to the problem. This solution will work if used pre-emptively, but where resistance has evolved to one member of a stack, resistance should easily evolve for the second gene in most cases. We propose and elaborate criteria that could be used to evaluate the value of stacked traits for pest resistance management. Stacked partners must: target the same pest species; be in a tandem construct to preclude segregation; be synchronously expressed in the same tissues; have similar tissue persistence; target pest species that are still susceptible to at least two stacked partners. Additionally, transgene products must not be degraded in the same manner, and there should be a lack of cross-resistance to stacked transgenes or to their products. With stacked herbicide resistance transgenes, both herbicides must be used and have the same persistence. If these criteria are followed, and integrated with other pest management practices, resistance may be considerably delayed. © 2016 Society of Chemical Industry.

Field‐evolved resistance by western corn rootworm to Cry34/35Ab1 and other Bacillus thuringiensis traits in transgenic maize

“…As such, managing western corn rootworm with a pyramid of Cry3Bb1 and Cry34/35Ab1 may no longer be a viable approach in some areas. Furthermore, due to widespread resistance to Cry3Bb1, the utility of this pyramid for delaying resistance to Cry34/35Ab1 will be diminished, and the risk of additional populations evolving Cry34/35b1 resistance will be enhanced …”

“…In both cases, pest resistance to one or more Cry toxins has been countered by cultivation of Bt maize containing a pyramid of Bt toxin VIP3A with the Cry toxins that have been compromised by resistance. However, in these cases, the resistance management benefit of pyramiding is greatly reduced by the presence of Cry resistance . The approach of using pyramids after resistance has developed is more akin to a pesticide treadmill than proactive resistance management .…”

“…Pyramiding of Bt toxins with DvSnf7 has the potential to delay pest resistance, compared to a scenario where DvSnf7 were present singly in transgenic maize . However, to the extent that western corn rootworm populations have already evolved resistance to Cry3Bb1 and Cry34/35Ab1, this will diminish the resistance‐management benefit of pyramiding and hasten the evolution of resistance to DvSnf7 …”

“…Under the pyramid‐refuge strategy, crop plants produce multiple Bt toxins that target the same insect pest, with individuals that harbor resistance alleles for one toxin in a pyramid killed by a second toxin . However, the effectiveness of delaying resistance with pyramids is reduced if cross‐resistance exists between toxins or if there has been evolution of resistance to either of the toxins in the pyramid …”

“…Resistance to Cry3Bb1 was subsequently found for western corn rootworm populations in Nebraska, Minnesota and Illinois . The presence of resistance to Cry3Bb1 is expected to diminish the resistance‐management benefit of pyramiding Cry3Bb1 with Cry34/35Ab1 . Furthermore, field‐evolved resistance to Cry3Bb1 has been found to extend to mCry3A and eCry3.1Ab through the presence of cross‐resistance .…”