Zoysiagrass genotype responses to Sphenophorus venatus vestitus (Coleoptera: Curculionidae).

The hunting billbug, Sphenophorus venatus vestitus Chittenden, is a pest that damages stems, rhizomes, and roots of zoysiagrass through a combination of adult and larval feeding. Management of this pest is difficult because it has multiple, overlapping generations in the southern United States, and symptoms of infestations are often misdiagnosed and inappropriately treated as drought stress or disease. Experiments were conducted in a greenhouse where 18 zoysiagrass cultivars were potted and infested with S. v. vestitus adults to examine the response of zoysiagrass genotypes to S. v. vestitus feeding damage. Results showed that zoysiagrass species and cultivars differed in susceptibility to S. v. vestitus, indicating that variable tolerance may exist in these turfgrasses for improvement through breeding. In general, Zoysia japonica Steudel was more susceptible to S. v. vestitus feeding damage and supported more S. v. vestitus than Zoysia matrella (L.) Merrill. Among the Z. japonica cultivars,'Belair' and'Zenith' had less desirable agronomic traits and incurred greater feeding damage than other cultivars more tolerant to billbug damage. With Z. matrella, 'Diamond' and 'Pristine Flora' displayed superior agronomic traits and had the least feeding damage and lowest infestations of billbug immatures and were therefore considered the most tolerant or resistant Z. matrella cultivars tested. Results indicate that stem diameter may be an important factor for adult feeding and oviposition site selection, which might explain the different responses between Zoysia spp. to S. v. vestitus damage.