How to Identify Weevils in Alfalfa

 

When scouting alfalfa, there are two species of weevils that may be observed. These two species are the alfalfa weevil and the clover leaf weevil. The alfalfa weevil is known to cause serious defoliation and has the greater potential to cause yield losses. However, clover leaf weevils can also become very damaging if present in large populations. Although they are similar in size and coloration, there are some distinguishing characteristics that can be used to identify these weevil species.

 

The larvae of alfalfa weevils have three pairs of legs and range in size from 1/16” when they first hatch to 5/16” when they are fully grown. During development, the larvae also vary in color depending on their age. Shortly after hatching, the larvae are light yellow-green (Figure 1) but will turn a darker green after feeding on plant material (Figure 2). The distinguishing characteristics of the alfalfa weevil are its dark brown-black head capsule and prominent white stripe that is present on its back and runs the length of the body. The adult alfalfa weevils are approximately ¼” long. They are light brown in color with some mottling and have a darker brown stripe that runs down their midline. The adults have an elongated snout that extends and curves down from the head. Their antennae originate on the elongated snout.