Adults: shiny, elongate, bluish black, 1/4-inch beetles with reddish brown thoraxes, four cream-colored spots and red borders on wing covers. Larvae: 1/3 inch, plump, wrinkled, and gray with dark heads and legs. Eggs: shiny, black, glued on end to stems and young spears. Common throughout North America. The spotted asparagus beetle (Crioceris duodecimpunctata) causes similar damage, but is generally found east of the Mississippi River. Beetles are red-orange with twelve black spots on wing covers; larvae are orange.
Adults and larvae chew on green asparagus shoots, blemishing spears; also attack older stems and leaves.
Hibernating adults emerge when first asparagus spears are ready to be cut; they feed and lay eggs on spears. Eggs hatch in 1 week, larvae feed for 2 weeks, then burrow into the soil to pupate. Adults emerge in 10 days. Two or three generations per year
In fall, remove and destroy old fronds and garden trash where beetles overwinter, or put it in sealed containers for disposal with household trash; in spring, cover spears with floating row cover until end of harvest; handpick beetles; as a last resort, spray pyrethrin.
Photo: Clemson University, USDA Cooperative Extension Slide Series, Bugwood.org