Tracking billbug (Sphenophorus spp.) seasonal biology with DNA barcodes and a simple morphometric analysis to inform management

Billbugs (Sphenophorus spp.), a complex of closely related grass-feeding weevils, damage the aesthetic and functional qualities of turfgrass. Although our ability to articulate efficient IPM strategies to growers hinges on an understanding of regional variation in species compositions and seasonal biology of these insects, the inability to identify the larval stage to species level has hindered these efforts. This gap in understanding is especially problematic in geographic areas across North America where the ranges of billbug species overlap. We used modern DNA barcoding methods and classical morphometric measures to fill gaps in understanding the seasonal biology of the billbug species complex across a broad geographic range. Adult billbugs from Indiana, Missouri, and Utah were collected and identified morphologically to species level. Cytochrome oxidase subunit 1 (COI) was amplified and sequenced to create a reference library against which unknown larval specimens could be compared and identified. Larval specimens were collected across the season in Utah and Indiana, and their head capsule diameters were measured as a proxy for development instar. COI was amplified, sequenced, and compared against the adult reference library. Sequences varied among billbug species, but the variation was not influenced by geography, indicating that this locus alone is useful for resolving larval species identity. Overlaid with head capsule diameter data from larval specimens, better visualization of billbug seasonal biology emerged. This provides the support necessary for researchers and extension specialists to make inferences about billbug biology that are needed to improve IPM strategies across a broad geographic range.