Minnesota field population of western corn rootworm (Coleoptera: Chrysomelidae) shows incomplete resistance to Cry34Ab1/Cry35Ab1 and Cry3Bb1

Abstract

In the United States of America, the western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is commonly managed with transgenic corn (Zea mays L.) expressing insecticidal proteins from the bacteria Bacillus thuringiensis Berliner (Bt). Colonies of this pest have been selected in the laboratory on each commercially available transformation event and several resistant field populations have also been identified; some field populations are also resistant. In this study, progeny of a western corn rootworm population collected from a Minnesota corn field planted to SmartStax® corn were evaluated for resistance to corn hybrids expressing Cry3Bb1 (event MON88017) or Cry34/35Ab1 (event DAS‐59122‐7) and to the individual constituent proteins in diet‐overlay bioassays. Results from these assays suggest that this population is resistant to Cry3Bb1 and is incompletely resistant to Cry34/35Ab1. In diet toxicity assays, larvae of the Minnesota (MN) population had resistance ratios of 4.71 and >13.22 for Cry34/35Ab1 and Cry3Bb1 proteins, respectively, compared with the control colonies. In all on‐plant assays, the relative survival of the MN population on the DAS‐59122‐7 and MON88017 hybrids was significantly greater than the control colonies. Larvae of the MN population had inhibited development when reared on DAS‐59122‐7 compared with larvae reared on the non‐Bt hybrid, indicating resistance was incomplete. Overall, these results document resistance to Cry3Bb1 and an incomplete resistance to Cry34/35Ab1 in a population of WCR from a SmartStax® performance problem field.

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

“…In cases where Cry34/35Ab1 resistance was found in this study, resistance ratios ranged from 9 to 19 (see Results), suggesting that the level of resistance found in the field has increased over time. Furthermore, one of the problem field populations (PF2) showed complete resistance to Cry34/35Ab1 maize, while past studies had only found incomplete resistance . This increase in resistance observed in the present study, compared to past studies, parallels results for western corn rootworm resistance to Cry3Bb1 maize, where resistance to Cry3Bb1 maize increased significantly over time for western corn rootworm populations from fields associated with high levels of feeding injury to Cry3Bb1 maize …”

“…Bt maize producing Cry34/35Ab1 was registered by the US EPA in 2005 and the first evidence of resistance was found in 2013 from fields in Iowa and Minnesota where high levels of feeding injury were observed for maize containing Cry34/35Ab1 . The results reported here indicate additional cases of resistance to Cry34/35Ab1 within the agricultural landscape.…”

“…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 .…”

“…Furthermore, field‐evolved resistance to Cry3Bb1 has been found to extend to mCry3A and eCry3.1Ab through the presence of cross‐resistance . Additionally, beginning in 2013, evidence emerged of field‐evolved resistance to Cry34/35Ab1 . Thus, current management of western corn rootworm using Bt maize is challenged by the presence of resistance to all currently available Bt traits in some populations.…”

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.…”