Asparagus beetle adults are about 1/4 inch long, oval in shape, brightly colored in blue and brown, with cream-colored elongate spots on the back. Spotted asparagus beetle is orange with many small black dots on the back. Asparagus beetles lay clusters of yellow eggs on the asparagus spears and ferns; spotted asparagus beetles lay similar eggs only on the ferns. The larvae of both species are soft-bodied, elongate, and about 1/4 inch long when full grown. Asparagus beetle larvae are gray; spotted asparagus beetle larvae are cream colored.
The adults chew notches in the spears, reducing their market value. Asparagus beetle eggs on the spears also reduce their market value. Both the larvae and adults of the asparagus beetle feed on the ferns. Severe fern damage can reduce spear production the following year.
Asparagus beetle overwinters as adults. The adults begin feeding immediately after emergence in spring. Egg laying begins one week after emergence. The eggs are laid in rows of 3 to 8 eggs on spears. Larval feeding lasts for about two weeks. The larvae feeds on spears. Mature larvae move to the ground and burrow in the soil where it pupates.
Spotted asparagus beetle larvae live and feed within the developing asparagus berries. The use of male-only varieties eliminates this beetle as a pest. Treat spears during the harvest season if infestations of either species exceed five to ten adults per 100 crowns, or if eggs are present on more than 2 percent of the spears. Treat ferns postharvest if infestations exceed five to ten adults per ten crowns.