Quantitative trait loci linked to survival of western corn rootworm on maize producing Bacillus thuringiensis toxin Gpp34/Tpp35ab1

The western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera:Chrysomelidae), is one of the most economically important insect pests of maize in North America, and remains difficult to manage due to field-evolved resistance to transgenic maize that produces insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt). Resistance to Bt maize that produces Gpp34/Tpp35Ab1 (formerly Cry34/35Ab1) occurs in multiple geographic regions, posing a threat to the long-term sustainability of this management practice. The genetic mechanisms of Gpp34/Tpp35Ab1 resistance remain unknown. To investigate this, we established two resistant strains of western corn rootworm with field-evolved Gpp34/Tpp35Ab1 resistance. Larvae from four F2 pedigrees from each strain were reared on seedling mats of Gpp34/Tpp35Ab1 maize or the non-Bt near isoline. Survivors were genotyped using an anonymous, double-digested restriction-site-associated DNA sequencing approach (ddRADseq). Single nucleotide polymorphisms (SNPs) were identified among ddRAD markers by alignment to a reference, chromosome-level, western corn rootworm genome assembly. Subsequent quantitative trait loci (QTL) mapping assessing co-segregation of ddRAD markers with categorical phenotype of survivorship on Bt or non-Bt maize identified putative regions on chromosomes that were associated with resistance. Functional annotation of genes within these QTL regions used Blast2GO to predict gene ontology. This integrated approach lays the groundwork for identifying candidate genes that may contribute to resistance and will inform future efforts to monitor and manage resistance in field populations of western corn rootworm.