Changes in corn rootworm wing morphology are related to resistance development
The western corn rootworm, Diabrotica virgifera virgifera LeConte, is the most serious pest of maize across the US Corn Belt and now Europe. The beetle has repeatedly demonstrated its ability to adapt to pest management strategies through evolution of resistance to conventional insecticides, the cultural practice of crop rotation and now to the Bacillus thuringiensis (Bt) toxin which is produced by genetically modified maize. In this study, the wing morphology of 358 western corn rootworm adults from Iowa, Indiana and Illinois, USA, was investigated using geometric morphometric procedures. The populations investigated comprised resistant (i.e. soybean–maize rotation and Bt-maize variants) and non-resistant beetle populations. Data analysis was divided into two groups: (1) resistant versus non-resistant and (2) rotation-resistant versus Bt-maize rootworm populations. Results showed that morphological differences exist in the hind-wing shape of both rotation and Bt-maize-resistant versus non-resistant populations and rotation-resistant versus Bt-maize-resistant variants. Across all three types of rootworm variants investigated, the movement of landmarks 8, 9 and 14 drove the wing shape differences found. These landmarks relate to the basal radial vein and are a key anatomical character used to distinguish different wing morphotypes in rootworm. This study demonstrates the utility of hind-wing morphology/shape as an inexpensive and accessible population biomarker for rootworm. With simple equipment (camera mounted microscopes or flatbed scanners) and readily available free software to capture and analyse landmark (shape and size) data, it is possible to effectively monitor pest resistance development and associated field-based population-level differences. The biological implications of the differences in wing shape found and how this relates to rootworm flight and consequently its dispersal and invasion capabilities are also explored.
KeywordsGeometric morphometrics Bt-maize Monitoring Resistance Hind wings
The authors are very grateful to: Wade French for Bt-maize-resistant rootworm colonies maintained at the United States Department of Agriculture, North Central Agricultural Research Laboratory (NCARL) in Brookings, South Dakota; and Joseph Spencer, Thomas Sappington and Larry Bledsoe for providing field-collected rotation-resistant and susceptible beetles from Iowa, Indiana and Illinois.
This study was funded by the Croatian Science Foundation project ‘Monitoring of Insect Pest Resistance: Novel Approach for Detection and Effective Management Strategies’.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
Western corn rootworm is an established pest of maize in the USA and Southern Europe. No special permission was needed for its collection in this study.
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