Asparagus Beetles Identification Guide

Asparagus Beetle Identification Guide

Asparagus beetles are one of the most common pests that garden asparagus growers deal with in North America. Two species cause problems. The common asparagus beetle (Crioceris asparagi) and the spotted asparagus beetle (Crioceris duodecimpunctata) both came from Europe. The common species was first found in North America in the 1860s. Today both species live wherever asparagus is grown across the United States and southern Canada.

Physical Characteristics

The common asparagus beetle is a small beetle about 6 to 9 mm long, or roughly 1/4 inch. It has an elongated body shape. The wing covers are dark bluish-black with cream or yellowish square spots and a red border along the edges. The plate behind the head is usually red with dark marks. The antennae are dark and short.

Key features for identifying the common asparagus beetle:

• Elongated oval body, 6 to 9 mm long
• Bluish-black wing covers with cream or yellowish spots, usually three on each side
• Red to orange-red border along the wing cover edges
• Red plate behind the head with dark marks
• Dark antennae and legs
• Shiny, dark eggs laid in rows on asparagus spears

The spotted asparagus beetle is a bit larger at 7 to 9 mm long. It has orange wing covers with twelve black spots, six on each side. It tends to show up about two weeks later in the season than the common species.

The larvae of the common species are plump grubs that grow to about 8 to 9 mm. They are gray to olive-green with a dark head and dark legs. You will rarely see larvae of the spotted species. They feed inside asparagus berries instead of out on the leaves.

Common Look-Alikes

Asparagus beetles can be mixed up with several other small, colorful beetles. Asian lady beetles share the orange-and-black colors of the spotted asparagus beetle, but lady beetles are rounder. Cucumber beetles are a similar size and show up in gardens, but they have different spot or stripe patterns. They also feed on squash and cucumber plants instead of asparagus. Flea beetles are much smaller and jump when you disturb them. Japanese beetles are bigger and have a metallic green and bronze color that looks very different.

The easiest way to confirm you are looking at an asparagus beetle is to check the plant it is on. These beetles feed almost only on asparagus.

Asparagus Beetle Behavior and Biology

Lifecycle and Development

Asparagus beetles go through four life stages: egg, larva, pupa, and adult. The full cycle from egg to adult takes about four to six weeks. Warmer weather speeds this up.

Overwintering. Adults spend the winter hiding in plant debris, old asparagus stalks, loose bark, and leaf litter near the beds. They go dormant when temperatures drop in the fall.

Spring emergence. When the soil warms in spring and asparagus spears start pushing up, the adults wake up and come out. In the Mid-Atlantic and Midwest, this happens in April or May. They start feeding on young spears right away.

Egg laying. Females of the common species stick their dark, shiny eggs in neat rows right on the spears and new shoots. One female can lay a few hundred eggs in her lifetime. The spotted species lays its eggs one at a time on the ferns, usually later in the season.

Larval feeding. Eggs hatch in about three to eight days. The larvae of the common species eat fern foliage, stripping the needles and leaving dark droppings behind. Spotted asparagus beetle larvae burrow into asparagus berries to feed. Larvae take about two weeks to finish growing.

Pupation. Full-grown larvae drop to the ground and pupate just under the soil surface. New adults come out in about five to ten days. They either start laying eggs for a new round or, if it is late in the season, find a spot to overwinter.

Two generations per year are common in the Mid-Atlantic. Cooler northern areas may see only one. Warmer southern areas can have overlapping generations that keep beetle numbers high through most of the growing season.

Feeding Habits and Damage

Both adults and larvae of the common asparagus beetle feed on the plant. Adults chew on spears, buds, and fern needles. Larvae eat mostly the fern foliage. Damage shows up in several ways:

• Scarring on spears from adult feeding makes harvested asparagus look rough
• Eggs stuck to spears make them hard to sell at farm stands and stores
• Stripped ferns where larvae and adults eat the needle-like leaves, turning the plant brown and bare
• Weakened root crowns over time because the plant cannot store enough energy for the next year

Young asparagus plants in their first few years are at the most risk. They have not built up strong roots yet. Older, well-set beds handle moderate feeding better, but they will still get weaker if beetles go unchecked year after year.

Treatment Methods for Asparagus Beetles

The best results come from mixing good garden habits, hands-on removal, and targeted treatments when numbers get too high.

Prevention and Cultural Controls

Good garden management goes a long way toward reducing beetle numbers:

• Clean up debris in fall. Remove and destroy old asparagus ferns and leaf litter after the season ends. This gets rid of the spots where adults hide for the winter.
• Harvest frequently. Picking spears daily or every other day removes eggs before they hatch and reduces the number of larvae that reach the fern stage.
• Monitor regularly. Check asparagus beds at least once a week during harvest and keep checking as ferns grow. Watch for adults on spears, eggs on shoots, and larvae on ferns.

Physical and Mechanical Controls

For home gardens and small plantings, hands-on methods work well:

• Hand-pick beetles and drop them into a bucket of soapy water. Adults often fall off the plant when you bump it. Hold the bucket below to catch them.
• Crush or remove egg rows from spears before or during harvest. The dark, shiny eggs are easy to spot against the green spears.
• Shake plants over a light-colored cloth to dislodge beetles and larvae for removal.

Biological Control

Several predators and parasites feed on asparagus beetles and can lower their numbers:

• Parasitic wasps in the genus Tetrastichus attack asparagus beetle eggs and can reduce numbers where they are present.
• Lady beetles and lacewings feed on eggs and small larvae.
• Ground beetles prey on larvae that drop to the soil to pupate.

Chemical Control Considerations

When beetle numbers get too high for other methods to handle, chemical treatments may be needed:

• Spinosad-based products work well against both adults and larvae. They are approved for organic production.
• Pyrethrin sprays give a quick knockdown of adult beetles but do not last long on the plant.
• Always check pre-harvest intervals before treating asparagus you plan to eat. Since asparagus is picked often during the harvest window, choose products with short waiting times.
• Switch between different product types so beetles are less likely to build up resistance.

References and Further Reading

• Virginia Cooperative Extension - Asparagus Beetles
• University of California Pest Management - Asparagus Beetles
• University of Minnesota Extension - Asparagus Beetles
• Cornell University - Asparagus Pest Management
• Animal Diversity Web - Crioceris asparagi