Painted Lady

Table of contents

    Painted Lady, Thistle Butterfly (Vanessa Cardui (L.))

    Larvae feed primarily on Canada thistle leaves, leaving the stem and midrib. Feeding temporarily inhibits the weeds but new growth usually develops in the fall. They also feed on about 60 other hosts, including sunflowers and canola.

    Identification and Life Cycle

    Figure 36. Painted Lady Larvae

    Photo by Roy Ellis

    Adults migrate into the prairies from overwintering sites in Mexico, arriving in early June. There is no evidence that they can survive our cold winters. This butterfly normally prefers to lay eggs on Canada thistle plants but under some conditions will lay eggs on other plants. Larvae feed on the leaves producing loose webbing and, if numerous, can completely defoliate a plant. The larvae are up to 30 mm (1.2") long and dark purple to black in colour (Figure 36). They have long spines on each segment of the abdomen.

    Management

    Because this occasional pest is usually limited to small, scattered patches within a field, insecticide treatments are rarely justified.

    The major concern with this normally beneficial insect arises when fecal pellets webbed on thistles are harvested with the canola seed. Grade standards have a low tolerance to insect excreta.