Evaluation of adult emergence and larval root injury for Cry3Bb1‐resistant populations of the western corn rootworm

Abstract

The transgenic maize (Zea mays L.) event MON 88017 produces the Bacillus thuringiensis Berliner (Bt) toxin Cry3Bb1 to provide protection from western corn rootworm (Diabrotica virgifera virgifera LeConte) larval feeding. In response to reports of reduced performance of Cry3Bb1-expressing maize at two locations in Illinois, we conducted a two-year experiment at these sites to characterize suspected resistance, as well as to evaluate root injury and adult emergence. Single-plant bioassays were performed on larvae from each population that was suspected to be resistant. Results indicate that these populations had reduced mortality on Cry3Bb1-expressing maize relative to susceptible control populations. No evidence of cross-resistance between Cry3Bb1 and Cry34/35Ab1 was documented for the Cry3Bb1-resistant populations. Field studies were conducted that included treatments with commercially available rootworm Bt hybrids and their corresponding non-Bt near-isolines. When compared with their near-isolines, larval root injury and adult emergence were typically reduced for hybrids expressing Cry34/35Ab1 either alone or in a pyramid. In many instances, larval root injury and adult emergence were not significantly different for hybrids expressing mCry3A or Cry3Bb1 alone when compared with their non-Bt near-isolines. These findings suggest that Cry34/35Ab1-expressing Bt maize may represent a valuable option for maize growers where Cry3Bb1 resistance is either confirmed or suspected. Consistent trends in adult size (head capsule width and dry mass) for individuals recovered from emergence cages were not detected during either year of this experiment. Because of the global importance of transgenic crops for managing insect pests, these results suggest that improved decision-making for insect resistance management is needed to ensure the durability of Bt maize.

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

“…In Iowa, for example, resistance to Cry3Bb1 appears to be ubiquitous within the agricultural landscape, with populations often exhibiting complete resistance ( i.e ., showing equivalent survival and development on Cry3Bb1 maize versus non‐Bt maize) . By contrast, resistance to Cry34/35Ab1 in the Midwest appears to be more heterogeneous in its distribution, being present in some populations but not others . Furthermore, to date, resistance to Cry34/35Ab1 in field populations of western corn rootworm appears to be incomplete, with populations showing reduced survival on Cry34/35Ab1 maize compared to non‐Bt maize .…”

Investigation of Cry3Bb1 resistance and intoxication in western corn rootworm by RNA sequencing

“…Different toxins from Bacillus thuringiensis Berliner with activity against WCR have been expressed in commercial corn hybrids, including Cry3Bb1, mCry3A, Cry34/35Ab1 and eCry3.1Ab (DiFonzo, 2017;Gassmann, 2016). Field-evolved resistance to Cry3Bb1, widespread in the U.S. Corn Belt (Gassmann, Petzold-Maxwell, Keweshan, & Dunbar, 2011, 2012Gassmann et al, 2016;Ludwick et al, 2017;Schrader, Estes, Tinsley, Gassmann, & Gray, 2017;Wangila, Gassmann, Petzold-Maxwell, French, & Meinke, 2015), confers cross-resistance to mCry3A (Gassmann et al, 2014) and eCry3.1Ab Zukoff et al, 2016).…”

Response of Cry3Bb1‐resistant western corn rootworm (Coleoptera: Chrysomelidae) to Bt maize and soil insecticide

“…In Iowa, western corn rootworm with field‐evolved resistance to Cry34/35Ab1 and eCry3.1Ab also has been identified (Gassmann et al., ; Jakka, Shrestha, & Gassmann, ). Additionally, resistance to various Cry proteins has been reported from Nebraska (Wangila, Gassmann, Petzold‐Maxwell, French, & Meinke, ), Illinois (Schrader, Estes, Tinsley, Gassmann, & Gray, ) and Minnesota (Ludwick et al., ; Zukoff et al., ). Jakka et al.…”