Seasonal Occurrence and Abundance of Billbugs (Coleoptera: Curculionidae) in Georgia Sod Farms.

Abstract

The billbug, Sphenophorus spp. (Coleoptera: Curculionidae), is an important pest complex in sod farms in Georgia. Larval feeding within stolons and on roots affects spring recovery of slow-growing zoysiagrass and poses a serious challenge to machine harvesting, as the damaged turfgrass rarely holds together. Little is known about major billbug species and their seasonal occurrence and abundance in Georgia sod farms, as most previous research was conducted in golf courses in the region. In 2018 and 2019, adult billbugs were sampled from five zoysiagrass sod field sites in central Georgia. Four linear pitfall traps were used per site from February to December each year, and the traps were checked at weekly intervals. The data show that >98% of the sampled billbugs were the hunting billbug, Sphenophorus venatus vestitus Chittenden, whereas the nutgrass billbug, Sphenophorus cariosus Olivier; uneven billbug, Sphenophorus inaequalis Say; and vegetable weevil, Listroderes difficilis Germain were the minor species. Seasonal billbug capture was influenced by turfgrass phenology (e.g., early-growth-stage, late-growth-stage or fully grown turfgrass). The numbers of Sphenophorus spp. collected were significantly greater in the fully grown turfgrass than in the early- or late-growth-stage turfgrasses. Significantly greater densities of billbug were found in Zoysia matrella (L.) Merrill ('Zeon') and the Z. matrella × Zoysia pacifica (Goudswaard) M. Hotta & S. Kuroki hybrid ('Emerald') than in the Zoysia japonica (Steudel) cultivars 'El Toro' and 'Zenith'. Similar numbers of male and female billbugs were collected from the sod field sites.