Black Vine Weevils

Adult black vine weevils will feed on over 100 different kinds of plants including trees, shrubs, vines and flowers. The preferred hosts seem to be Taxus (yews), hemlock and various rhododendrons. Taxus capitata seems to be particularly susceptible to attack. This pest is often called taxus weevil by the nursery industry. It commonly infests containerized perennials in greenhouse and polyhouse production settings. Occasionally, adults and larvae will attack potted house plants, especially ones placed on the porch for the summer.

The black vine weevil, Otiorhynchus sulcatus (Fabricius), has been reported as being accidentally imported from Europe and was first detected in Connecticut in 1910. However, there is evidence in the scientific literature that this species was actually detected in the 1830's. It was probably introduced along with some plant material brought from Europe. Mainly through movement of ornamental plants, the black vine weevil has been spread across much of northern North America from Maine to the Carolinas and west to Washington and Oregon.

Life Cycle

Female weevils emerge from soil pupation chambers late May to early July. These weevils must feed on plant material for 21 to 45 days before they are ready to lay eggs. After the preoviposition period has passed, the females place several eggs each day into the soil or leaf litter nearby suitable host plants. The weevils hide during the daytime at the base of plants or in mulch and leaf litter near food plants. Adults may live 90 to 100 days and usually lay 200 eggs during this time.

The eggs hatch in two to three weeks and the small C-shaped, legless larvae feed on plant rootlets. The larvae grow slowly over the summer, molting five to six times. By late fall the larvae have matured and are about 5/8-inch long. The mature larvae enter a quiescent prepupal stage in an earthen cell and pupate the following spring. A single generation occurs each year.

Control of Black Vine Weevils

These weevils are difficult to control once established because of their nocturnal behavior, the subterranean habits of the larvae, and the lack of natural predators or parasites.

Habitat Modification - Egg and larval survival is helped when soil moisture is moderate to high in July and August.

Biological Control Using Parasitic Nematodes - The nematodes have been effective for controlling black vine weevil larvae, especially in potted plants. Sufficient water must be used during application to wash the infective nematodes into the soil and root zone.

Soil Drenching with Insecticides - This technique has not worked well for larval control unless moderately soluble, long residual insecticides are used. Most pesticides get bound up in the organic matter under plants and never reach the larvae.

Foliar Sprays of Insecticides - Since the adults are active after dark, the most common method of control is to place a stomach poison on susceptible plant foliage. Because adults are active for a long period, several sprays may be needed. Early applications are encouraged so that adults are affected prior to their egg laying period.