Identification
The asparagus beetle, Crioceris asparagi, and the spotted asparagus beetle, C. duodecimpunctata, may both be found in gardens. In California C. asparagi is more likely to be found. Larvae are dark green-gray grubs about 3/4 inch (9 mm) long when full grown. Asparagus beetle adults may be bluish black beetles with a red prothorax and yellow spots and red borders on wings. Spotted asparagus beetles are reddish orange beetles with black spots.
Life Cycle
Adult beetles overwinter in garden debris, especially old ferns. They emerge when spears first emerge. Beetles feed and lay dark brown eggs singly or in rows on spears. Eggs hatch in 3 - 8 days. Larvae are blue gray with black heads and feed on plant tips. Mature larvae drop to the ground and pupate just below the soil surface. A new generation of adults emerges in 1 - 2 weeks. After spears are harvested, beetles and grubs feed on ferns. There may be up to five generations a year.
Damage
Adults of the asparagus beetle chew the growing tips of spears in spring leaving brown stains, scars, or blemishes. Larvae may chew ferns, causing them to appear bleached. Spotted asparagus beetle larvae feed primarily inside berries while adults do minor damage to ferns.
Solutions
Remove spears promptly. Handpick beetles or wash eggs, larvae, and adult beetles off with a strong stream of water. Clean up debris and remove and destroy ferns by proper pruning in late fall to reduce overwintering sites for adults. Avoid insecticides because of potential harm to parasites and predators, and damage is not usually serious enough to warrant it. Applications of a pyrethrin spray may be effective against larvae when they are young.
