Billbugs have been reported as serious pests of lawns and other turf areas since the late 1800's. Today, we know of at least eight turfgrass-damaging species, the most important of which are the bluegrass billbug, Sphenophorus parvulus, the hunting billbug, S. venatus, and the "Denver" billbug, S. cicatristriatus.
Billbug larvae (grubs) appear similar to white grubs but are legless. They have cream-colored bodies with brown heads, and when fully developed are about 1/4 to 1/2 inch long, depending on the species. Their bodies are slightly curved and appear similar to a grain of puffed rice. Bluegrass Billbug The bluegrass billbug was first reported as a turfgrass pest in Nebraska in 1890. Today, this insect is recognized as a serious pest of Kentucky bluegrass nearly wherever the grass is grown. Although preferring Kentucky bluegrass (as its name implies), the bluegrass billbug also feeds on perennial ryegrass, fescue and timothy. Adult bluegrass billbugs are typical weevils (or snout beetles) with mouthparts located at the end of a curved snout or bill. These insects, which are about 1/4 inch long and dark brown to black, are slow moving and frequently "play possum" when disturbed. From April to June and again in September and October they can often be observed crawling on sidewalks and driveways near infested turf. Hunting Billbug The hunting billbug resembles the bluegrass billbug, but is slightly larger and has parenthesis-like markings on the back of the thorax. The grasses most seriously damaged by this billbug are zoysiagrass and bermudagrass, although injury to St. Augustinegrass and centipedegrass has occurred. Kentucky bluegrass is only occasionally damaged by this billbug species. The hunting billbug is a pest primarily in the southeastern U. S., but is also found in mid-Atlantic states, and further west and north into Missouri, Kansas and southeast Nebraska. Denver Billbug Comparatively little is known concerning the biology and life history of the Denver billbug. Damage from this insect has been reported from Colorado, Kansas, and western and central Nebraska. It is probably the most important billbug infesting Kentucky bluegrass lawns in Colorado and some areas of western Nebraska. Adult Denver billbugs are considerably larger than either the bluegrass billbug or the hunting billbug, reaching 1/3 to 1/2 inch in length. This billbug can be differentiated from the other two species by its larger size and the presence of distinctive, double-lobed markings on the wing covers.
Bluegrass and hunting billbugs typically have only a single generation each year, although a partial second generation of the bluegrass billbug has been reported in some areas. Both billbugs overwinter as adults in sheltered locations in and around infested turf. In southern states, hunting billbugs may also overwinter as larvae or pupae. The Denver billbug also overwinters as an adult, but is more likely to spend the winter as a mid-to-late-stage larva. Depending on springtime temperatures and geographic location, adult bluegrass and hunting billbugs become active in mid-to-late spring, with Denver billbug adults emerging a few weeks later (early May to June). After mating, females of all three species deposit their eggs in cavities chewed into plant stems near the crown. Newly-hatched larvae feed for 2 to 3 weeks within stems before migrating to the crown and root zone of the plant and continue to feed on roots and underground stems. Billbug larvae usually feed just below the thatch layer, but are occasionally found as deep as 2 to 3 inches in the soil profile. When larval feeding is completed (mid-July for bluegrass and hunting billbugs), pupation takes place in the soil or thatch. Adults begin to emerge in late July, feed for a brief period, then move to overwintering sites in leaf litter in protected areas such as hedges, tall grass, and around houses.
The greatest injury from billbugs usually occurs from mid-June through late July during the period of maximum heat and drought stress. In areas where the Denver billbug is present, damage also occurs in the fall and early spring. Because billbug injury is easily mistaken for white grub or sod webworm damage, disease, or even plant stress, the damaged turf area should be carefully examined to confirm the presence of billbugs before making a management decision. Knowledge of prior billbug infestations in a turf area will be useful in making a diagnosis. Newly-hatched billbug larvae tunnel in grass stems, hollowing out the stem and leaving fine sawdust-like plant debris and excrement. Infested stems discolor and when pulled, readily break away at or near the crown. Subsurface feeding by older larvae can completely destroy the plant's root system, causing the turf to appear drought stressed. Under heavy billbug pressure it will eventually turning brown and die. Adult billbugs also feed on grass stems and blades, but cause only minor injury to the turf. Billbug damage rarely occurs in turf stands less than three years old.