Tracking billbugs (Sphenophorus spp.) and generalist predators to advance biocontrol in Intermountain West turfgrass

Billbugs (Sphenophorus spp.) are the most problematic insect pest to turf in the Intermountain West. Most of what is known about billbug phenology comes from studies done on bluegrass billbug in the eastern U.S., and several aspects of their biology have yet to be validated in our region. In addition, little is known about predator communities in turf in the region or their potential to aid in billbug suppression. We examined the seasonal activity of billbugs and generalist predators in turfgrass to improve our understanding of timing of augmentative biocontrol applications and the potential impact of conservation biocontrol for billbug management. Adult billbugs and ground active predators were sampled weekly using linear pitfall traps on four golf courses in central Idaho and northern Utah. We found a complex of three species including bluegrass, hunting, and Rocky Mountain billbugs, with bluegrass being the most abundant. Eastern models predict first adult occurrence between 280 and 352 DD₅₀. However, we observed first occurrence several weeks earlier (16 -20 DD₅₀), and adult activity peaked in late May (318-444 DD₅₀). We found carabids and spiders to be the most abundant predatory taxa, and the activity of both groups overlapped that of billbugs. These data will be used to validate a degree-day model to optimize timing of management for billbugs. In addition, conservation of predators appears promising for billbug suppression given the overlap in activity, yet more understanding of the direct and indirect effects of predators on billbug populations is warranted.