Ecology and Behavior of the Hunting Billbug Sphenophorus venatus vestitus in Warm-Season Turfgrass

The hunting billbug, Sphenophorus venatus vestitus Chitenden, is a small, black weevil pest of turfgrass in the United States. Since 2000 there has been an increase in frequency of warm-season turfgrass damage due to hunting billbugs. More information on the biology and behavior of this pest in warm-season turfgrass is necessary to develop an economical and environmentally-friendly management plan. The objectives of this research project were: a) determination of overwintering stage, b) determination of oviposition cycle, c) how soil moisture affects larval development, d) evaluation of synthetic insecticides for control of adults and larvae, e) development of a technique to determine hunting billbug feeding behavior, f) determination of the level of damage produced by adult hunting billbugs in warm and cool-season turfgrass, and g) determination of feeding behavior in warm and cool-season turfgrass using previously mentioned technique. Overwintering studies were conducted in a bermudagrass stand (Cynodon spp.), with a known infestation of hunting billbugs from 2010-2013 in Raleigh, NC. Submersion of turfgrass and soil samples in a salt solution yielded 24 adults, 2 small larvae, 8 medium larvae, and 10 large larvae over all three years. Oviposition studies were conducted weekly for three years, where the number of eggs each female adult hunting billbug oviposited was recorded daily for 7d. Females oviposited consistently for the duration of the collection period in all years. Soil moisture effects on larval development were conducted with sandy soil at moisture levels of 80, 60, 40, or 20% of total porosity. Medium-sized larvae developed best in containers maintained at levels of 20% of total porosity occupied by water. Greenhouse evaluation of synthetic insecticides against adult hunting billbugs found neonicotinoid and pyrethroid products provide the greatest mortality. Evaluation of synthetic insecticides against larval hunting billbugs found similar results as adult trials, however overall percent control was too low to base recommendations for control. Adult hunting billbug feeding behavior was determined through the use of digital image analysis and an enzyme-linked immunosorbent assay (ELISA) developed to test for the presence of purified goat IgG treated on either the shoots or roots of the turfgrass plant. Feeding behavior trials using digital image analysis in warm and cool-season turfgrass found that 60% of the warm-season turfgrass trials had differences among billbug treatments, while 12% of the cool-season turfgrass trials had differences among billbug treatments. The data did not indicate a trend in average percent green cover among photograph dates. Feeding behavior trials using an ELISA assay found that the protein was not translocated within the plant or leached into the soil, was able to be removed from the insect exoskeleton, and was detected in the insect gut. Beetles exposed to treated bermudagrass and zoysiagrass shoots had a 50% and 8% chance, respectively, of testing positive for purified goat IgG. Beetles exposed to treated shoots of tall fescue and treated roots of bermudagrass, zoysiagrass (Zoysia spp.), or tall fescue (Festuca arundinacea) did not test positive. The results of these studies have provided a better understanding of hunting billbug biology and behavior in warm-season turfgrass. This information has allowed us to develop a management plan that focuses on season-long monitoring of adult hunting billbugs. This will inform turfgrass a manager when adults become active in the spring, thus indicating that oviposition begins. Tracking rain events after adults have reached peak abundance in the spring will inform managers of larval survival likelihood. If visible damage is associated with billbug populations, a treatment with a pyrethroid or neonicotinoid product when adults have reached peak abundance will maximize effectiveness of application and reduce environmental inputs.