Weevils are a very large group of beetles containing more than 60,000 species. Their larvae are fat-bodied, sluggish, legless, whitish, with a brown head and well-developed mandibles. They are most frequently to be found in the soil where they bite and chew fine roots. Some larvae burrow into the root nodules, some bore into the tap root, some bore into herbaceous stems. Adult weevils are about 8 mm long, dull grayish brown, with a V-shaped pale mark near the middle of the back. They have prominent snouts and a small pointed process towards the rear of each wing cover.
One generation occurs a year but adults may live two years or more. The juvenile weevils (grubs) of vegetable weevil (Listroderes difficilis) live above ground and feed on the foliage of plants rather than the roots. They particularly favor broadleaf weeds such as capeweed and marshmallow weed. The larvae grow up to 13 mm long and are colored green, yellow-green, or cream. When larvae finish feeding, they form a smooth-sided earthen cell in which they pupate. Adults emerge in spring or fall. During summer, adults remain inactive hibernating under debris or tree bark until autumn when they become active.
Vegetable weevils commonly damage germinating crops. Grubs and adults feed on the crowns of plants, foliage, and stems. Seedlings are at most risk, which may be attacked by both larvae and adults. The stem feeding is either partially through the stem, causing a weakening of the seedling, or the stem is completely cut off. The damage is similar to that of cutworms. However, these beetles do not eat as much leaf and stem tissue as cutworms. Vegetable weevils make large open holes in surface of potatoes and sometimes consumes buds and foliage. Because adults cannot fly, infestation of new areas takes place slowly and damage within the area may be spotty.
Checking seedling crops for the presence of larvae and adults is best done at night, when weevils usually feed. Young plants can be protected with cloth. Sticky barriers can be used to keep beetles from migrating into new areas of the garden. In case of heavy infestation, dust plants with a small amount of diatomaceous earth.
Some plants contain or give off compounds that repel insects. Companion planting is the practice of strategically placing insect-repelling plants next to crops that will benefit from their repellent effects. For example, planting garlic among vegetables helps to deter Japanese beetles, aphids, vegetable weevils, and spider mites.