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Thistle Caterpillar

Thistle Caterpillar (Painted Lady) Vanessa cardui (Linnaeus) Description: The body of the adult is about 1 inch long with a wingspan of about 2 inches. The upper wing surfaces are brown with red and orange mottling and white and black spots. Each hind wing has a row of four distinct and obscure eyespots. Eggs are small, spherical and white. The larvae are brown to black and spiny, with a pale yellow stripe on each side. Mature larvae are 1.25 to 1.5 inches long.

Life Cycle: It is indigenous to the southern U.S. and migrates annually to the northern region including Canada where it breeds. It returns to the south for overwintering. Eggs are laid on Canada thistle, wild and cultivated sunflower and a number of other host plants. Larvae feed on sunflower in late June/early July. Webbing is formed around the larvae. This insect is multi-generational.

Scouting Method: An X pattern should be used counting 20 plants per sampling site to determine percent defoliation. Infestations will often be concentrated where Canada thistle is abundant. Economic Threshold: The threshold is 25 % defoliation if the larvae are less than 1.25 inches long. If the majority of larvae are 1.25 to 1.5 inches long, most of the feeding damage has occurred and control is not advised. Management: Damage from this insect is usually not economic. There have been instances where spot spraying within a field has been warranted. Photos: Visit the Photo Gallery. Another resource about Insects can be found in the Archive section of The Sunflower magazine. Source: NDSU Extension Bulletin 25 Sunflower Production, NDSU Extension Service, September 2007

High Plains Sunflower Production Handbook  file size: 1554 kb

NDSU Extension Bulletin 25 - Revised 9/2007 file size: 5591 kb