Alfalfa weevil

Alfalfa weevil biology & life cycle

Adults overwinter in the crowns of alfalfa or under debris near fields. Females oviposit into dead stems or ground litter and later into greening stems. Young larvae bore within the stem until reaching the growing tip, where they feed on developing leaves. Mature larvae construct a pupal case consisting of yellow-orange latticework. New adults emerge and feed for a few weeks before entering summer dormancy in late July; they may emerge and feed again in autumn. Adults and larvae feed on stems, growing tips, leaves and buds. Older larvae feed on buds and skeletonize leaves. Adults feed along leaf margin. Stems may be damaged during oviposition.

Identifying Alfalfa weevil

Alfalfa weevil: eggs

Eggs can vary in color from shiny yellow to brown. They can be found in clusters of 2-25 in the stems of the host plant.

Alfalfa weevil: larvae

Young larvae white and legless; mature larvae 8 mm long, green with black head and white stripe down middle.

Alfalfa weevil: Pupae

Tan in colour, within lace-like cocoons.

Alfalfa weevil: adult

4-5 mm long, light to dark-brown wiht broad-brown longitudinal stripe running down middle of back with a downward pointing snout, clubbed and elbowed antennae.

Alfalfa weevil: management

Examine plant stems for oviposition punctures and survey for abundance of adults. Heavily damaged alfalfa fields have a greyish white or frosted appearance.