Black Vine Weevil (and Other Root Weevils)

ENT-49
Date: 
04/20/2015
David J. Shetlar and Jennifer E. Andon, Department of Entomology

The black vine weevil, Otiorhynchus sulcatus (Fabricius), earned its name "vine" weevil as it was first documented as a pest on grapes in Germany. It 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 as early as the 1830s. Mainly through the transport of ornamental plant material, the black vine weevil (BVW) has been spread across southern Canada and throughout much of the northern half of the United States. This pest currently extends from Maine to the Carolinas and west to Washington and Oregon and occurs in all counties in Ohio.

Black vine weevil adult

There are several close relatives of the black vine weevil, the strawberry root weevil, O. ovatus (Linneaus), the rough strawberry root weevil, O. rugosostriatus (Goeze), and the clay-colored weevil, Otiorhynchus singularis (Linneaus). These pests are collectively called root weevils because their larvae feed on a variety of plant roots. The strawberry root and rough strawberry root weevils are often found in seedling nurseries, nursery polyhouses and occasionally in small fruit farms. The clay-colored root weevil occurs in the western United States and primarily feeds on raspberries. The latter three weevils rarely cause significant damage in Ohio. The BVW is the most destructive of the vine weevil complex, both in landscapes and plant nurseries.

Plants Attacked

Adult black vine weevils will feed on over 100 different species of cultivated and wild plants including trees, shrubs, vines and flowers. The preferred hosts seem to be Taxus (yews), hemlock, various rhododendrons and other broad-leaved evergreens. Taxus capitata seems to be particularly susceptible to attack, giving this pest the name "taxus" weevil by the nursery and landscape industry. Other susceptible plants include begonia, cyclamen, fuchsia, impatiens, primrose and sedum. 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.

 

Damage

Black vine weevil adult notching

Adult weevils cause insignificant, aesthetic injury to plants by feeding on the margins of leaves, creating crescent-shaped notches. Careful searches should be made to locate the insect pest as multiple other weevils, and some caterpillars can produce this same type of notching. Moderate to light notching seems to have little effect on plant health. The legless larvae prefer to feed on young tender roots of Taxus, rhododendrons and hemlock from mid-summer through fall and in early spring. More mature larvae may even feed on larger roots or bark. If young roots become scarce or the soil becomes overly moist in the fall, larvae are forced to move toward the surface, where they may feed on the stem of host plants. If the stems are girdled, the resulting damage will ultimately lead to death, as the flow of nutrients and water has been disrupted.

Injury to Taxus has appeared throughout Ohio, particularly in northeastern counties where nurseries are located on sandy loam soils. This pest can also reach epidemic populations in polyhouses where liners and perennials are being grown. Occasionally, hundreds of field-grown plants are killed with dramatic suddenness. Perennial producers occasionally open their polyhouses in the spring, only to find that many of the plants are dead because all their root systems have been eaten away.

Description and Life Cycle

Black vine weevils are oblong oval in shape, about ½ inch long and have a short, broad snout with elbowed antennae. The body is slate gray to blackish brown and the wing covers have numerous small pits and short hairs. This pest is difficult to distinguish from other Otiorhynchus weevils. The strawberry root weevil is usually half the size of the black vine weevil, and more brown in color. The rough strawberry root weevil is only slightly smaller than the black vine weevil but the collar just behind the head, the pronotum, is heavily pitted. Otiorhynchus weevils are generally parthenogenic in North America, meaning the female reproduces asexually. As a result, population growth occurs very quickly. Only females are produced. These insects are nocturnal and undergo only a single generation in Ohio. Multiple generations may occur for populations infesting plant material in greenhouses.

Black vine weevil larvae

Female BVW emerge from soil pupation chambers in 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 near 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 ⅝ 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 outdoors.

These weevils cannot fly but they are very active walkers. They are easily transported in potted plants or transplants using a soil root ball.

In the warmth of house plant pots or nursery polyhouses, the larvae may pupate in January or February and the adults emerge in March or April.

Control Hints

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. Prevention should be the goal in pest management. With careful inspection of nursery stock and the quarantine of any suspicious material, infestations may be greatly reduced.

Strategy 1: Habitat Modification

Egg and larval survival is helped when soil moisture is moderate to high in July and August. Heavy mulches also help maintain critical moisture levels. Remove excessive mulch layers and do not water plants unless necessary. Excessively damp soils in the fall also force larvae to move up the base of the plant where girdling can occur. Properly maintain rain downspouts and provide for adequate drainage of soil around plants.

Strategy 2: Biological Control Using Parasitic Nematodes

The entomopathogenic nematodes, Steinernema and Heterorhabditis spp., 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. If the nematodes are to be used in landscape plantings, remove as much of the mulch as possible and thoroughly wet the remaining thatch and soil before and after the nematode application. Application of nematodes in landscapes has produced variable results. In polyhouse perennial production areas, nematodes should be applied to the pots in September when the soil media is still above 55°F.

Strategy 3: Chemical Control Targeting Adults

Several contact/stomach and systemic insecticides are effective at controlling BVW adults. Killing the adults before they are able to feed and produce eggs is most effective in landscapes and can help reduce populations in nurseries. New females emerge when black locust trees are in full bloom. Since females can be active for two months, two or more applications of insecticides may be necessary.

Strategy 4: Chemical Control Targeting Larvae

Achieving control of weevil larvae is very difficult in landscapes and nurseries where organic matter (i.e. mulch) is high. There are only a few insecticides that can be used as soil drenches. Container plants can be drenched, preferably in August or September.


This fact sheet is a revision of OSU Extension fact sheet HYG-2016, Black Vine Weevil.

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