Field-evolved resistance by western corn rootworm to multipleBacillus thuringiensistoxins in transgenic maize

Abstract

Significance Crops genetically engineered to produce insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt) kill pest insects and reduce the use of conventional insecticides. However, the evolution of Bt resistance can diminishes these benefits. The western corn rootworm is a serious pest of maize and is managed with Bt maize. Beginning in 2009, western corn rootworm with resistance to maize producing the Bt toxin Cry3Bb1 imposed severe injury to Cry3Bb1 maize in Iowa. We show that cross-resistance exists between Cry3Bb1 maize and mCry3A maize and is associated with severe injury to Bt maize in farmers’ fields. These results illustrate that Bt crops producing less than a high dose of toxin against target pests may select for resistance rapidly; consequently, current approaches for managing Bt resistance should be reexamined.

Evidence of Resistance to Cry34/35Ab1 Corn by Western Corn Rootworm (Coleoptera: Chrysomelidae): Root Injury in the Field and Larval Survival in Plant-Based Bioassays

“…1). Field visits followed established protocols described in Gassmann et al (2014). At each field, the location was recorded using a global positioning system (GPS; Legend HCX, Garmin, Olathe, KS).…”

“…Newly hatched neonates were used in plant-based bioassays following Gassmann et al (2014). Briefly, plants were grown singly in Fig.…”

“…In general, we hypothesized that resistance to a specific Bt toxin would be present in a western corn rootworm population when corn with that Bt toxin suffered high levels of injury in the field (e.g., severe feeding injury to Cry3Bb1 corn would be associated with Cry3Bb1 resistance). In cases where resistance to Cry3Bb1 was present, we hypothesized that mCry3A resistance also would be present because of previous research indicating cross-resistance between these Bt toxins (Gassmann et al 2014, Wangila et al 2015. …”

“…Similarly, resistance to Cry3Bb1 corn and crossresistance between Cry3Bb1 and mCry3A was identified for western corn rootworm populations from Nebraska (Wangila et al 2015), and resistance to Cry3Bb1 corn has been confirmed in Illinois (Schrader et al 2016). To date, however, western corn rootworm populations have not developed resistance to Cry34/35Ab1 corn (Gassmann et al 2011(Gassmann et al , 2014Wangila et al 2015).…”

“…Beginning in 2009, fields in Iowa were identified with severe feeding injury to Cry3Bb1 corn, and subsequent bioassays found that this injury was associated with resistance to Cry3Bb1 corn (Gassmann et al 2011). Fields with Cry3Bb1-resistant western corn rootworm also were collected in Iowa during 2010 and 2011, and cross-resistance was identified between Cry3Bb1 corn and mCry3A corn (Gassmann et al , 2014. Similarly, resistance to Cry3Bb1 corn and crossresistance between Cry3Bb1 and mCry3A was identified for western corn rootworm populations from Nebraska (Wangila et al 2015), and resistance to Cry3Bb1 corn has been confirmed in Illinois (Schrader et al 2016).…”