BLACK VINE WEEVIL
Otiorhynchus sulcatus (Fabricius), Curculionidae, COLEOPTERA
CAUTION: This information was developed for North Carolina and may not apply to other areas
The black vine weevil is about 3/8 inch long and has a short snout. The thorax and wing covers are bumpy. The body is blackish brown; the antennae are black. The egg is smooth and shiny. It is white when first deposited but becomes brown as it ages. The legless, white grub grows to 1/2 inch long. Its body is curved with a brown head. The pupa is white with tiny spines on the head, abdomen and legs.
Black vine weevil larvae stunt or kill plants by feeding on the roots. Larger roots are stripped of their bark or girdled, or they have notches chewed out of them. The adult weevils chew the edges of the leaves, cut off the tips of needles or devour entire needles. Foliage is preferred to terminal growth.
Black vine weevils overwinter as mature larvae. However, a few adults also survive the winter to feed and deposit eggs during a second season. This weevil is parthenogenetic. Although one female was recorded as laying 863 eggs, the average number of eggs deposited by each female is probably about 200. During the preoviposition period which lasts about 4 weeks, the adults feed most extensively. Adults usually live 90 to 100 days. Eggs, deposited in the soil and leaf litter, hatch in 2 to 3 weeks. Initially, the young larvae feed on rootlets; but after the third molt, the larvae move to the larger roots. During their development, the larvae molt five or six times within earthen cells in the soil.
After a quiescent prepupal stage that lasts from 3 weeks to 8 1/2 months, the larvae pupate. Three weeks later, adults emerge. Adults feed at night and drop from the plant, feigning death when disturbed. These weevils cannot fly so they must be carried or must crawl to uninfested areas.
A 1997 study in California showed a great reduction of black vine weevil in commercial planters using parasitic nematodes, Steinernema feltiae (327/in2) or Heterorhabditis bacteriophora (474/in2). The use of nematodes could be a viable alternative to chemicals, especially in sensitive public areas.
Washington State has a list of Rhododendron varieties resistant to black vine weevil damage available in PDF. The University of Georgia has identified Azalea varieties somewhat resistant. Not all varieties may be suited to NC.
Pesticides may be applied to the media or soil surface as a drench to control black vine weevil larvae. Imidacloprid (Merit, Marathon) can be used as a soil injection or drench against larvae. Scimitar & Demand (Oregon study) and Talstar (Ohio study) are effective when adults are present. Aloft may also be an effective product. Apparently, carbaryl (Sevin), malathion and isofenphos (Oftanol) are not effective for black vine weevil control. The standard Orthene is felt to be effective, but has shorter residual than the pyrethroids.
In Ohio, they found that adults begin to emerge in late May when black locust is blooming and recommend the first application soon thereafter when multiflora rose is in mid-bloom. They found adult emergence to be fairly synchronous (based on presence of pupae in the soil), peaking in mid-June and being largely done by July 4, with a tail distribution of stragglers emerging until mid-July. Timing sprays with bloom periods in NC should be expected to hold. Use three sprays at three week intervals. For labeled pesticides, see the North Carolina Agricultural Chemicals Manual under the headings: Trees and Woody Ornamentals, Plant:Any, Black vine weevil.
See also: Insects and Other Pests Related to Trees and Shrubs AG-189 .
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
Web page last reviewed January, 2011 by the webperson .