Alfalfa Caterpillar

Common: Alfalfa Caterpillar

Scientific: Colias eurytheme

Crop Hosts: Alfalfa

Identification and Life Cycle: The insect overwinters in the pupal stage on the plants. In the spring the overwintering pupae change to yellow butterflies. They lay 200 to 500 eggs singly on the underside of the alfalfa leaves. The eggs hatch in a few days and the dark grass-green worm feed on the leaves and when mature form a pupa without spinning a cocoon. The adult emerges in 5 to 7 days. In the South, there can be 5 to 7 generations with 2 being the norm in the more northern states.

Geographical Distribution: Throughout the United States with the heaviest damage occurring in alfalfa-growing regions of the western states.

Damage and Treatment: Infested fields show partly to wholly consumed leaves. Yields can be drastically affected.

Treatment should be made when insect populations and/or damage levels reach economic thresholds. Refer to local University Extension Pest Management Guidelines for specific state thresholds.