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Genetic and morphometric monitoring for management of western corn rootworm resistance

The western corn rootworm (WCR) is a highly invasive pest of maize. It has developed resistance to insecticides and established management strategies. The objective of this study is to determine the differences between WCR laboratory populations from the United States that are resistant to various Bt toxins and non- resistant population by combining genetic and geometric morphometric analyzes. For the morphometric analyzes, 775 hindwings of Bt- resistant and susceptible WCR populations from laboratory cultivation in the USA were used. Fourteen specific points (markers) were used to assess variability in hindwing shape and size. Principal component analysis (PCA) and canonical discriminant analysis (CVA) were used. The research results showed the significant differences in US populations resistant to different Bt toxins. To confirm these results, we used the single nucleotide polymorphisms (SNPs) method for a detailed whole genome analysis. Forty-five WCR individuals were genotyped. Individuals were subjected to standard population genetic analyzes, and the resulting genotypic data were analyzed for: expected (HE) and observed (HO) heterozygosity, FIS and θ (FST) to determine the alteration of individual alleles as a possible consequence of mutations and the development of resistance to some of the Bt toxins. After quality filtering of the SNP data, we retained 7, 229 SNPs for further data analysis. Preliminary results based on the one- population model showed moderate observed heterozygosity (HO = 0.3206). Moderate genetic diversity estimated by expected heterozygosity (HE = 0.302). Moderate inbreeding was also observed (FIS = 0.1271). There were no significant deviations from HWE on all loci. The low value of pairwise FST = 0.0179 estimated suggests a lack of genetic differentiation and structuring among the putative populations. The use of these modern and innovative techniques (i.e., SNPs and geometric morphometrics) to detect resistant variants is a completely novel approach and provides new insights into a very important area of pest management.

Diabrotica virgifera virgifera, geometric morphometry SNPs, Bt toxins

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