While there are two different species of the asparagus beetle, both get their name by destroying the young growth asparagus spears and its foliage.
The most common of the species is the Crioceris asparagi, also known as the common asparagus beetle. The destructive pest is ¼ inches long and metallic bluish-black with creamy white dots and red markings on their wings.
The spotted asparagus beetle is similar to the markings of a lady beetle with a reddish-orange body and black spots. While the beetle can be harmful to asparagus plants, it is not as destructive as the common asparagus beetle.
The larvae of both species grow to be ⅓ of an inch in length and take on a slug-like appearance. However, the common larvae are green or grey with a black head, while the spotted larvae species is orange.
The common asparagus beetle will lay its eggs on young asparagus spears that have just emerged from the soil.
The larvae of the beetle hatch in about a week and start their journey by crawling up the plant and feeding as they do. After a few weeks, the larvae fall into the soil and pupate. After 7 days, an adult beetle emerges from the ground and starts the reproduction process all over again.
The spotted asparagus beetle will follow soon after, laying a single egg on the fronds of the plant. The larvae of the spotted beetle feed on the berries of older asparagus plants, then drop a few weeks later into the soil to pupate. In about 2 weeks an adult spotted asparagus beetle will emerge and begin reproduction until about July.
The damage caused by both the adult and larva of the common asparagus beetle often can be seen when growing spears take on a twisted hook-like appearance.
When the beetle feeds, it causes scarring and staining as they chew and deposit excrement caused by their feeding. Once the weather begins to turn warm, the beetles move on to feed on the ferns of the plant which in turn can prevent future growth of spears.
To control asparagus beetles, gardens can remove the adult beetles and their larvae by picking them off of the stalks of the young emerging plants to reduce the chances of a heavy infestation of the pest.
Beneficial insects such as the ladybug will consume the eggs and larvae of the bothersome pest, preventing future infestation of the bad bug.
Beneficial nematodes can also be introduced when infestations are heavy since the tiny enemy organisms will destroy the pupae of the asparagus beetle before they can become adults and reproduce.