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The rice billbug is a glossy, black or dark brown beetle in the weevil family Curculionidae, although some place it in a separate family, the Dryophthoridae. The small chewing mouthparts are located at the tip of the rostrum, a long, stout snout on the front of the head. The antennae are elbowed (geniculate). As with other beetles, adults possess sclerotized, hardened forewings called elytra that cover the abdomen and hind wings. The body shape is elongate and subcylindrical, with dorsal ridges containing short brown hairs (setae) on the pronotum and elytra. Males and females may be distinguished based on differences on the underside of the thorax (metaventrite). Males possess a row of stiff setae on the metaventrite, and these setae are lacking in females.
The larvae (grubs) are white to pale yellow, legless, with C-shaped bodies and a red-orange head capsule. Pupae are pale yellow and resemble soft, compact versions of the adults. Billbug eggs are 1 mm to 2 mm long, oblong in shape, creamy white, smooth and glossy.
More than 60 species of Sphenophorus are known to occur in the United States with at least 13 species in Louisiana based on specimens identified in the Louisiana State Arthropod Museum. Due to similarity among species, identifications of Sphenophorus should be performed by a knowledgeable specialist or entomology diagnostician.
The biology of the rice billbug is not well studied but is likely similar that of other members of the genus Sphenophorus occurring in Louisiana, such as the hunting billbug (Sphenophorus venatus vestitus) and clay-colored billbug (Sphenophorus aequalis), which are closely related. Differences in host plants, larval stage numbers and seasonality have been documented among studied species. As with all beetles, billbugs undergo four life stages (holometaboly): egg, larva, pupa and adult. The rice billbug’s life cycle begins with egg laying. The females create holes at the base of rice plants, either on the stem or beneath the soil’s surface, depositing a single egg in each. After hatching, larvae tunnel through and feed on the inner plant tissues near the soil surface. Larvae undergo five growth stages (instars) and require 30 to 40 days to mature and transform into the pupal stage. Then they pupate in the stem or beneath the soil surface, emerging as adults during late summer. These adults overwinter in organic matter along the edges of fields and reemerge during spring, dispersing by crawling or flying.
The rice billbug poses a significant threat to furrow-irrigated rice. While its complete host range is uncertain, it may feed on other grasses in the absence of rice. As rice production shifts away from traditional flood irrigation, the rice billbug has emerged as the primary weevil pest, replacing the rice water weevil, Lissorhoptrus oryzophilus. Some researchers speculate that rice is a good host because of its high vigor and tiller development. Adult billbugs enter a rice field at the early tillering stage. Their feeding during this time can result in tiller termination; however, the economic impact is unknown. In furrow-irrigated rice, adults feed at or near the soil line or at leaf whorls. Feeding at the rice heart can result in tiller death or “dead heart.” Larvae feed on the root crown and lower stems, potentially causing plant death. Their feeding damages vascular tissue, inhibiting panicle development and resulting in seedless panicles (whiteheads). Because this injury is identical to other well understood stem boring pests (Lepidoptera: Crambidae), the yield loss relationship with billbug feeding is estimated to be 1.7% yield loss for every additional whitehead.
There are no established thresholds for rice billbugs in rice, and specific impacts of this pest are largely unknown. In other described species of Sphenophorus, feeding occurs on agricultural grasses and weedy grass species. Adults do not fly well, so they are primarily ground active and overwinter in plant litter and unmanaged turf and grasses. Researchers speculate that the rice billbug has similar habits, which suggests that unmanaged field edges serve as refuges. Scouting for dead tillers during early season can be effective to determine presence of billbugs, but it is not helpful in determining population density. Destructive sampling techniques, such stem splitting, are currently the only recommended scouting methods. Billbug feeding cavities are typically filled with powdery, white frass.
Limited research has been conducted to determine rice billbug control. Currently, other weevil species are controlled using insecticide seed treatments. However, preliminary research at the LSU AgCenter has demonstrated that seed treatments are ineffective against billbugs and do not improve yield. Single foliar application of neonicotinoids during the early-boot stage is the only known effective tactic. Rice billbug research is being conducted at the University of Arkansas, Mississippi State University and Louisiana State University. Contact your local cooperative extension service for control recommendations if you notice symptoms or infestations.
Schyler Thibodeaux
Christopher E. Carlton
Rice billbug adult feeding at base of rice plant (Tyler Musgrove, LSU AgCenter).
Dorsal and ventral views of rice billbug (Lindsey Seastone, Museum Collections: Coleoptera, USDA APHIS PPQ, Bugwood.org).
Rice billbug “white head” damage in rice (Tyler Musgrove, LSU AgCenter).
P3996
6/13/2025
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