A new artificial diet for western corn rootworm larvae is compatible with and detects resistance to all current Bt toxins

Dalton C Ludwick,Man P Huynh,Thomas A Coudron,Bruce E Hibbard,B Wade French,Lisa N Meihls,Adriano E Pereira

doi:10.1038/s41598-018-23738-z

Abstract

Insect resistance to transgenic crops is a growing concern for farmers, regulatory agencies, the seed industry, and researchers. Since 2009, instances of field-evolved Bt resistance or cross resistance have been documented for each of the four Bt proteins available for western corn rootworm (WCR), a major insect pest. To characterize resistance, WCR populations causing unexpected damage to Bt maize are evaluated in plant and/or diet toxicity assays. Currently, it is not possible to make direct comparisons of data from different Bt proteins due to differing proprietary artificial diets. Our group has developed a new, publicly available diet (WCRMO-1) with improved nutrition for WCR larvae. For the current manuscript, we tested the compatibility of all Bt proteins currently marketed for WCR on the WCRMO-1 diet and specific proprietary diets corresponding to each toxin using a susceptible colony of WCR. We also tested WCR colonies selected for resistance to each protein to assess the ability of the diet toxicity assay to detect Bt resistance. The WCRMO-1 diet is compatible with each of the proteins and can differentiate resistant colonies from susceptible colonies for each protein. Our diet allows researchers to monitor resistance without the confounding nutritional differences present between diets.

Highlights

Western corn rootworm (Diabrotica virgifera virgifera LeConte, western corn rootworm (WCR)) has been a challenge for maize (Zea mays L.) farmers throughout much of the United States of America (USA) for decades
The WCRMO-1 diet was tested with each Bt protein alongside the proprietary diet of the corresponding registrant using a Bt-susceptible colony (Brookings-ND, Table 1)
We documented that differences between WCR colonies selected for resistance to each Bt protein and a control WCR population can be detected in diet toxicity assays with the WCRMO-1 diet (Table 2, Figs 1–3)

Summary

Introduction

Western corn rootworm (Diabrotica virgifera virgifera LeConte, WCR) has been a challenge for maize (Zea mays L.) farmers throughout much of the United States of America (USA) for decades. Attempts at managing WCR in the USA focused solely on crop rotation to a non-host such as soybean (Glycine max (L.) Merrill) or sorghum[1]. When they became available, management tactics included the application of insecticides for larval or adult management[4,5]. Biotechnology has allowed farmers to grow maize which expresses one or more proteins from Bacillus thuringiensis Berliner (Bt). Biotechnology has allowed farmers to grow maize that expresses one or more proteins from Bacillus thuringiensis Berliner (Bt) for WCR control. Bt maize products targeting WCR have not yet met the high-dose criterion[22], and this likely is a primary reason that the refuge strategy designed to delay resistance has been ineffective with this pest[23]

Methods

Results

Conclusion