Biology and management of billbugs (Coleoptera: Curculionidae) in turfgrass
Billbugs (Coleoptera: Curculionidae: Sphenophorus spp.) are a complex of weevil pests affecting turfgrass throughout the United States. Billbug larvae cause damage by feeding in stems, on roots, and on the crowns of turf, causing severe discoloration and eventual plant death. Monitoring efforts have focused on nondestructive pitfall sampling of ground-active billbug adults and on destructive sampling using soil cores for larval stages in the soil. Given the cryptic nature of the susceptible larval stages, billbugs are typically managed by preventive applications of long-residual, systemic insecticides, including neonicotinoids and anthranilic diamides. Despite knowledge of effective management practices including pest-resistant turf varieties, irrigation management, and microbial controls that contribute to an IPM approach, billbug management continues to rely heavily on prophylactic synthetic insecticides. This review will summarize the identification and biology of billbugs and strategies for their management.Turfgrass covers >164,000 km2 (63,321 mi2) of the United States landscape, over three times the land area of any other irrigated crop (Milesi et al. 2005), and includes golf courses, home lawns, sports fields, and sod farms (Gelernter 2012). In 2005, the revenue generated by the turfgrass industry exceeded US$62 billion (Haydu et al. 2008), surpassing the combined value of corn (US$21 billion) and soybeans (US$17 billion) in the same year (NASS 2006). This revenue depends largely on maintenance of turfgrass quality, aspects of which include density, texture, growth habit, smoothness, and color (Beard 1972). Management practices that enhance turfgrass quality, like regular irrigation, fertilization, and mowing, however, encourage many species of turf-feeding arthropods (Held and Potter 2012). Turf is grown primarily for its utility and appearance, and discoloration of turfgrass can quickly become unacceptable in settings such as golf courses and sod farms, whose revenues depend largely on turf health and quality. Feeding by billbug (Coleoptera: Curculionidae: Sphenophorus spp.) larvae in stems and on roots causes spotty patches of yellow and brown turf, which can expand to large areas of dead grass. Thus, billbugs can be a serious pest of turfgrass, but effective management has been historically difficult due to several aspects of billbug biology, which will be discussed in this review. Billbugs are a complex of weevils native to and widespread throughout the United States (Johnson-Cicalese et al. 1990, Shetlar et al. 2012). The genus Sphenophorus contains 71 species, 64 of which occur in North America (Niemczyk and Shetlar 2000). At least 10 species are pests of turfgrass in the United States, including the bluegrass billbug (Sphenophorus parvulus Gyllenhal) and hunting billbug (S. venatus vestitus Chittenden), which are considered most harmful to cool-season grasses and warm-season grasses, respectively (Potter and Braman 1991, Vittum et al. 1999). Though billbugs have been known to infest other agricultural crops such as corn (Zea mays L.), wheat (Triticum aestivum L.), and range grasses (Satterthwait 1931a, Asay et al. 1983, Kuhn et al. 2013), they were first recognized as a serious pest of turfgrass when bluegrass billbug began to outbreak in several states in the 1960s (Tashiro and Personius 1970). These outbreaks were thought to be caused by resistance of the bluegrass billbug to pesticides that were heavily used at the time and the resulting reduction in natural enemy populations (Tashiro and Personius 1970). Billbugs continue to be problematic for turfgrass managers throughout the country.