Whitney Cranshaw, Colorado State University, Bugwood.org
Both beetles are of similar size with adults approximately 8mm long. However, there are tremendous differences in coloration between all life stages except the pupa.
Eggs for the asparagus beetle are oval shaped, dark brown, about 1.5 mm long. Eggs are usually found in groups of 3 to 8 oriented in a row and attached by one end to the host plant. Eggs of the asparagus beetle are most commonly found on the spear. The larvae of the asparagus beetle are dark gray with a black head. Pupa are in a light yellow silken cocoon. The adult asparagus beetle has a black body with a metallic blue head. On each wing cover there are three rectangular metallic yellow spots that frequently have red markings along the margin.
Spotted asparagus beetle
Eggs from the spotted asparagus beetle are green and oviposited singularly. Eggs are oval shaped and attached to the host plant by the side. Eggs of the spotted asparagus beetle are most commonly found on the fern. Larvae are cream colored with a light brown head and will most frequently be found inside the berry on female plants. Pupa are light yellow in a silken cocoon. Adult spotted asparagus beetles are orange with 6 black spots on each wing cover.
Both the asparagus beetle and spotted asparagus beetle overwinter as adults and begin feeding immediately following emergence. The asparagus beetle emerges slightly earlier than the spotted asparagus beetle. Oviposition begins approximately a week after emergence. While both adults feed on the spear, the placement of oviposition differs. The asparagus beetle oviposts on the spear in rows of 3 to 8 eggs while the spotted asparagus beetle oviposits eggs singularly on the fern. For both species larval feeding lasts for 10-14 days and 4 instars. Asparagus beetle larvae feed on the spear while spotted asparagus beetle will burrow into the berry. Mature larvae crawl to the ground and burrow within the soil where they spin a silken cocoon in which to pupate. In Pennsylvania it is common to have two generations a year.
The asparagus beetle damages asparagus in a number of ways. Adults and larvae feed on the tips and spears giving them a scarred appearance. Frass from both of these stages can stain the spear and oviposition on the spear can make them very unappealing. Any of the above deformities on spears can make them unmarketable.
Larvae of the spotted asparagus beetle feed on the berry of the female plant. For this reason infestations of the spotted asparagus beetle are less damaging than the asparagus beetle for fresh market and processing asparagus. However, the spotted asparagus beetle can be a major pest in seed production fields.
In small patches handpicking can control asparagus beetles. A method for larval control in small gardens is to brush the plants with a broom. This has the effect of knocking the larvae to the ground. The larvae have difficulty reclaiming the plant and will often expire on the ground.
Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.
Authored by: Shelby Fleischer, Associate Professor