Common Name: Pecan weevil
Scientific Name: Curculio caryae (Horn)
Description: Adult pecan weevil adults are 3/8 inch long, brownish beetles with snouts as long as the body. Larvae or grubs are legless, creamy white and have reddish-brown heads which grow to 3/5 inch long.
No other insects develop in pecan kernels in the field, although larvae of several pests, such as the Indianmeal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), can infest stored pecans. Hickory shuckworm, Cydia caryana (Fitch) (Lepidoptera: Tortricidae), larvae occur in shucks of pecan nuts. Acorns of live oaks in urban areas of North Central Texas are sometimes 100 percent infested by larvae of acorn weevils. Several species occur, but the most common is Curculio fulvus Chittenden (Coleoptera: Curculionidae). These species can be a problem in the production of oak trees from seed. Adult and larval acorn weevils are similar in appearance to pecan weevils and often occur around homes surrounded by oak trees. Larvae and pupae become common in flower beds and gardens in which acorns have fallen.
Life Cycle: Adult weevils and full grown larvae spend the winter in cells, 4 to 12 inches deep in the soil. Larvae pupate in late summer or fall. Adult weevils become active in August and early September. Mated females chew a hole in the pecan shell and deposit eggs inside. Larvae feed inside the nuts from late summer through the fall, growing and developing through several stages (instars). In late fall and early winter, about 42 days after eggs are laid, full-grown larvae chew a 1/8 diameter hole in the shell and drop to the ground. They burrow into the soil and construct a cell where they remain for 8 to 10 months before pupating and transform to adults, although some larvae do not pupate and transform to adults until the following year. Adults remain in cells and emerge from the soil a year later. The entire life cycle takes 2 or 3 years.
Habitat and Food Source(s): Mouthparts are for chewing. Adult weevils feeding and egg laying on developing (water stage) pecan nuts, causing them to drop from the tree. Larval stages develop in more developed nuts (dough stage), destroying the kernels. In most years, larvae damage results in the most yield loss. Adults can be sampled with emergence traps in the soil or with a beating sheet. Pieces of burlap bags or other cloth tied around a pecan tree trunk in late August so that a flap (appearing as an upside-down V in cross section) is formed will trap adult weevils crawling up the tree trunk after they emerge from the soil, where they can be collected.
Pest Status: Larvae feed in developing pecan nuts, causing yield loss. It occurs only in north central Texas and is absent from Waco toward the Gulf coast; medically harmless.
Management: See Managing Insect and Mite Pests of Commercial Pecans in Texas.
Literature: Crocker et al. 1987; Holloway 1980. Holloway et al. 1984.