A survey of billbugs (Sphenophorus spp.) in turf to improve management in the intermountain west

Billbugs (Sphenophorus spp.) have been identified by turfgrass managers as the most problematic insect pest to turf in the Intermountain West. Billbug larvae feed in stems and on roots of turfgrass, causing severe discoloration and possible plant mortality. Most of what is known about billbug phenology comes from studies done on bluegrass billbug in the eastern U.S. However, first occurrence of adult activity, timing of oviposition, and duration of larval stages in soil have not been validated in our region. The objective of this survey was to determine seasonal activity of billbugs to improve management in the Intermountain West. Adult billbugs were sampled weekly using linear pitfall traps on three golf courses from Boise, ID, to Logan, UT. To assess immature life stages in soil and stems we examined soil cores bi-weekly. We found a complex of three species made up of the bluegrass, hunting, and Rocky Mountain billbugs. Eastern models predict first adult occurrence between 280 and 352 DD₅₀. However, we observed peak adult activity in mid-June (540 DD₅₀) and first occurrence before 217 DD₅₀—at least one week earlier than current models. Eggs were deposited in late May, and the damaging larval stage was most abundant in late June to early July. These data will help assess factors (e.g. elevation and soil moisture) contributing to variation in billbug populations among sites and validate a degree-day model to optimize timing of management for billbugs in the Intermountain West.