The common asparagus beetle (Criocercis asparagi) and spotted asparagus beetle (Crioceris duodecimpunctata) are annual pests of asparagus in Wisconsin. The common asparagus beetle is the more prevalent of the two insects and the only one that consistently causes economic damage to asparagus.
Appearance: Adults of both the common and spotted asparagus beetle have slim, elongated bodies with hard wing covers and are approximately ¼ inch in size. The common asparagus beetle is bluish-brown with cream-colored spots, while the spotted asparagus beetle is orange with black spots. Eggs of both species are 1/8 inch long, shiny, dark, and rod-shaped. Eggs of the common asparagus beetle are laid in groups and are oriented in rows, whereas eggs of the spotted asparagus beetle are laid singly. Larvae of both species resemble slugs and are plump, wrinkled, and have visible legs. Larvae of common asparagus beetles have a cream to grey color with dark heads and legs, whereas those of the spotted asparagus beetle have orange bodies.
Symptoms and Effects: Both adult and larval asparagus beetles can cause direct plant damage and/or a reduction in asparagus spear quality. Common asparagus beetles typically feed on asparagus spears and ferns (leaves). Spotted asparagus beetles more commonly feed on asparagus berries. Feeding on spears causes browning, scarring and distorted growth, rendering the spears unmarketable. The presence of eggs, as well as insect feces (a black fluid), on the spears also reduces marketability. Later season feeding on ferns, particularly if asparagus beetle populations are high can lead to defoliation that will reduce yield in subsequent years.
Life Cycle: Both common and spotted asparagus beetles overwinter as adults in plant debris or mulch. Adults become active as asparagus plants emerge in early May. In general, common asparagus beetles become active earlier in May than spotted asparagus beetles (which often do not appear until late May). Common asparagus beetles lay eggs on emerging asparagus spears, while spotted asparagus beetles lay eggs on ferns. Eggs hatch approximately one week after they are laid. Larvae feed for approximately two weeks before they pupate in the soil and new adults emerge from pupae after approximately one week. Two to three generations of both species of asparagus beetle can occur in a single growing season.
Scouting Suggestions: Start watching for asparagus beetles in early spring and continue to monitor throughout the growing season. Scout in the afternoon when temperatures and sunlight are at their peak and when asparagus beetle adults are most active. In large asparagus plantings, in spring, examine twenty plants at each of five different locations after spears have emerged from the soil. In the summer, examine ten plants at each of five different locations. See scouting thresholds below to help determine the timing of chemical treatments. Spring scouting is designed to reduce damage to spears while later-season scouting is designed to reduce long-term damage caused by defoliation.
|Adults||5-10% of plants infested|
|Eggs||2% of spears with eggs|
|Larva||50-75% of plants infested|
|Defoliation||10% of plants defoliated|
Cultural: Destroy crop residue to eliminate overwintering sites for asparagus beetles. Also consider releasing the tiny parasitic wasp (Tetrastichus asparagi), which is an egg parasitoid of the common asparagus beetle and can reduce populations of this insect by up to 70%. If asparagus beetle populations are high, try using floating row covers early in spring to prevent damage to spears, but remove them after harvest is complete.
Chemical: If insecticides are needed to reduce asparagus beetle populations below threshold levels, you do not have to treat an entire planting. You can spot treat areas where threshold levels have been exceeded. Keep in mind that new plantings tolerate less injury than established plantings and may require more intensive chemical management. See the University of Wisconsin-Madison Division of Extension bulletin A3422 (Commercial Vegetable Production in Wisconsin), available at https://learningstore.extension.wisc.edu/, for detailed insecticide recommendations.
For more information on asparagus beetles: See UW-Extension Bulletin A3422 (available at https://learningstore.extension.wisc.edu/), or contact your county Extension agent.
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