Vegetable weevil—Listroderes costirostris obliquus
Weevil larvae are green, legless grubs about 0.38 inch long when full grown. Adults are small (0.38 inch long) brown or gray snout beetles with a V-shaped spot at the tip of the wings. They cannot fly. Vegetable weevils have only one generation a year, but adults may live 2 years or more.
There are more than 1,000 species of weevils or snout beetles in California. The most common pest weevil species in California is the black vine weevil, Otiorhynchus sulcatus. Other important species include the cribrate weevil, Otiorhynchus cribricollis, fuller rose beetle, Asynonychus godmoni, obscure root weevil, Sciopithes obscurus, strawberry root weevil, Otiorhynchus ovatus, vegetable weevil, Listroderes costirostris, the woods weevil, Nemocestes incomptus, the rough strawberry root weevil, O. rugosotriatus, and the Douglas-fir twig weevil, Cylindrocopturus furnissi.
Both adults and larvae feed on buds, foliage, and roots of potatoes, tomatoes, carrots, lettuce, and other vegetables. Adults do not fly, so infestation of new areas takes place slowly and damage within the area may be spotty. Both adults and larvae are most active at night and can be difficult to find in the daylight. Young plants may be cut at ground level or defoliated.
Little is known about management for the vegetable weevil. Young plants can be protected with cloth. You may be able to prevent localized infestations from spreading by destroying infested rows or picking off weevils at night. Sticky barriers can be used to keep beetles from migrating into new areas of the garden. Formulated mixtures of the botanical insecticides pyrethrin or azadirachtin may provide some control. Spot treatments may be all that is necessary.