Common Name: Alfalfa weevil
Scientific Name: Curculionidae: Hypera postica
Status: Key insect pest of alfalfa
Damaging Stage: mostly larval; occasionally adult

Biology: The alfalfa weevil is a major pest of alfalfa and often requires chemical treatments to manage. The adult beetle is a small, dark grey or brown beetle approximately � inch long with a prominent brown snout and a distinct dark band that extends down the back.

Immature alfalfa weevils are always legless and have black head capsules. The first two instars are generally brown in color, but the third and fourth instars are always green and have a characteristic white line down the middle of the back. Immature alfalfa weevils grow to approximately 3/8 inch in length.

Injury: Alfalfa weevil larvae are important pests of alfalfa because they stunt the growth of alfalfa plants and significantly reduce harvest potential. In late spring, the eggs hatch and the larvae begin to feed. For the first few days, the larvae feed within the stem but then move to the leaf buds at the tips of the stems. Here their feeding causes significant defoliation and stunting of the plant growth. As time progresses, their feeding gives the leaves a skeletonized appearance.

Action Threshold: The key to economical management of alfalfa weevil is combining crop management practices, biological control, and the use of insecticides when weevil numbers are high enough to ensure that yield benefits outweigh treatment costs. Before the first cutting, the threshold is generally 35�40 percent of plants with feeding damage. After the first cutting, the action threshold is eight or more larvae per square foot or where larval feeding is suppressing regrowth.

Management: Management of alfalfa weevil can be accomplished by monitoring closely. Decisions about insecticide applications must be made in relation to the population of weevils, the growth of the plant and expected time of cutting.