Asparagus Beetle

Asparagus Beetle, Crioceris asparagi , and the spotted asparagus beetle, Crioceris duodecimpunctata, are pests of asparagus. Distinguishing between the two species is important because the common asparagus beetle is more prevalent and causes more damage.

The adult beetle is smooth, shiny, slightly elongated, and slightly over 1/4 inch long. It has a metallic blue head and bluish-black wing covers, each with three yellowish, squared spots and a red outer margin. The thorax is reddish with two small blue spots. The eggs are elongate, dark brown in color, and attached by one end to the host plant. Larvae are plump, humpbacked, wrinkled, and sluggish. They are dark gray in color with black heads. To date, only 7 counties have reported the occurrence of this pest. However, it is expected to continue to spread through the state.

Asparagus beetle 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.

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.

Life Cycle :The adults of the common asparagus beetles overwinter in sheltered places such as piles of rubbish and heaps of old asparagus tops. The beetles emerge from their shelter and begin feeding on the tender tips of new shoots. They soon lay eggs on the young shoots. The eggs are elongate, oval, and deposited either singly or in rows of two to eight. Later in the season the eggs are laid on leaves and flower stems. The eggs hatch in three to eight days and the grubs begin feeding on the tender tips.

When the grubs mature, they drop to the ground and construct a small earthen cell where they transform into pale yellowish pupae. The adult beetles emerge from the pupae. There may be two or more generations a year depending on the climate. The adult spotted asparagus beetles overwinter in piles of debris. They leave their winter quarters about one week later than the common asparagus beetles and begin to feed on the tender young shoots as well.

They do not deposit eggs until the plant begins to blossom, about three weeks after emergence. The egg is deposited singly on plants, usually those bearing fruit. The egg is 0.5 mm (1/25 inch in length, olive brown, and attached to the leaf by one side. The larvae of the spotted asparagus beetle hatch in seven to twelve days and are yellowish-orange in color with a black head and legs.

The larva finds a berry and enters it at the blossom end. Inside the berry it feeds on the seeds and it may attack three or four berries before it is mature. When fully grown, it drops to the ground by a silken thread and spins a cocoon just under the soil surface.

Damage :Feeding on the spears by both species of asparagus beetle adults can cause browning, scarring and may cause asparagus spears to bend over into a shepherd’s crook. When the ferns appear later in the growing season, the common asparagus beetle larvae and adults can also devour the ferns.

Significant defoliation can weaken the plant and reduce the plant’s ability to provide sufficient nutrients for the following season. Serious defoliation can also make asparagus more susceptible to invasion by Fusarium, a fungal pathogen. The feeding of spotted asparagus beetle larvae on berries does not affect the health of asparagus plants over the long run. Numerous eggs of the common asparagus beetle laid on the spears can make the asparagus unappealing.

Management : Start scouting plants in early May or just after asparagus plants emerge and continue throughout the remainder of the growing season. The best time to check for asparagus beetles is in the afternoon when they are most active.

Protect your plants if one out of 10 plants have either species of adult asparagus beetles (10% or more), or if 50% to 75% of the plants have common asparagus beetle larvae, or if you see two out of 10 spears (20% or more) with dark brown, oval-shaped eggs. Management isn’t necessary for spotted asparagus beetle larvae since they feed on the berries and occur later in the season.

Handpicking, especially in small gardens, can be effective. Drop adults and larvae in a pail filled with soapy water. Also remove the dark brown eggs from the spears. New adult beetles can fly into the garden, so be sure to check your asparagus regularly. Handpicking is less practical in large gardens.

Sanitation practices, such as elimination of plant residue in and around the asparagus will decrease the number of overwintering sites available to adults. A tiny (less than 1/8-inch) metallic green wasp, Tetrastichus asparagi, parasitizes asparagus beetle eggs . You may notice these wasps when working in your garden. They can sometimes provide very effective control, parasitizing up to 70% of the eggs. Lady beetle larvae and other predators may also be active, and will consume both eggs and larvae. Most insecticides, however, will also kill beneficial predators and parasites.

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