Distribution. Asparagus beetle is found throughout North America wherever asparagus is grown. This insect is of European origin, and was first observed in the western hemisphere at Long Island, New York, about 1856. It spread rapidly in the northeast and midwestern states and eastern Canada, and reached California in 1904, Oregon and Washington in the 1910s and 1920s, and British Columbia in 1926. This species is invariably more abundant than the co-occurring spotted asparagus beetle, Crioceris duodecimpunctata (Linneaus).
Host Plants. Asparagus beetle feeds only on asparagus. Asparagus has escaped cultivation and grows wild throughout the northern United States and southern Canada wherever there is adequate moisture. These wild plants, as well as homegarden plants, are the principal food resources of asparagus beetle. Regular harvesting, and especially insecticide application, generally keep asparagus beetle from attaining high densities on commercial crops. Nevertheless, in northern climates it occasionally is damaging. California, a major producer of commercial asparagus, is relatively free of asparagus beetle problems; hot weather likely is the basis for few problems in California and southern states.
Natural Enemies. Several general predators and parasitoids are known from asparagus beetles. The lady beetles Coleomegilla maculata Mulsant and Hippo-damia convergens Guerin-Meneville, Coccinella transver-soguttata Brown, and Coccinella novemnotata Herbst (all Coleoptera: Coccindellidae) feed on eggs and larvae. Larvae also are attacked by the stink bugs, Perillus bio-culatus Fabricius and Stiretrus anchorago (Fabricius) (both Hemiptera: Pentatomidae) and the assassin bugs, Sinea sp., Pselliopus sp., and Arilus cristatus (Linnaeus) (all Hemiptera: Reduviidae).
The most important mortality factor is Tetrastichus asparagi Crawford (Hymenoptera: Eulophidae), which feeds on young eggs and parasitizes older eggs. The wasp uses her ovipositor to puncture the egg and then, in young eggs, applies her mouthparts to the puncture. She then sucks the contents from the chorion, causing collapse of the egg, but the egg remnants remain attached to the plant. In Massachusetts, about 50% of eggs are fed upon by T. asparagi, and a similar proportion of the survivors is parasitized (Capinera and Lilly, 1975a). Although parasitized larvae complete their development, they perish after forming their pupal cell. A mean of 4.75 parasitoids develops in each parasitized beetle larva. The parasitoids, which are specific to C. asparagi, are well-synchronized with their hosts, and emerge in time to feed on and parasitize the subsequent generation (Capinera and Lilly, 1975b; van Alphen, 1980). There are three generations annually. The biology of this parasitoid was given by Russell and Johnston (1912), and Johnston (1915).
There have been attempts to relocate parasitoids and to increase parasitism rates. T. asparagi was shipped from Ohio to the west coast in the 1930s and successfully established in Washington, but not in California (Clausen, 1978). Additional species of para-sitoids were imported from Europe, and one, Lemopha-gus cioceritor Aubert (Hymenoptera: Ichneumonidae) is likely established in Ontario (Hendrickson et ah, 1991).
Life Cycle and Description. The number of generations is probably three throughout this insect's range, though there is some speculation that there may be more generations in mild climates. In Ontario, Taylor and Harcourt (1975, 1978) reported three generations, with peak egg-laying in early June, July, and August. This was found consistent with observations from Massachusetts, though only a portion of the adults from the second generation produced eggs. Thus, the third generation was very small (Capinera and Lilly 1975a), giving the impression of only two generations. This species overwinters as adults.
are black, the body is rather plump, and the tip of the abdomen bears anal prolegs, which help to anchor the larva to the plant while it feeds. There are four instars. Mean development times are about 1.6, 1.7, 2.2, and 6 days for instars 1-4, respectively, at 26°C. The rate of development increases from about 10°C, the lowest temperature at which development occurs, until the upper limit of development is attained at about 34°C. At 32-34°C, larval development is completed in about 7.9 days. When survival rates at various temperatures are considered in addition to development rates, optimal temperature for larval asparagus beetle is about 30-32°C. Taylor and Harcourt (1978) used temperature relations to predict accurately the development of beetle populations under field conditions in Ontario. (See color figure 105.)
Pupa. Mature larvae drop to the soil and construct pupal cells from oral secretions and soil particles. The pupa resembles the adult beetle except for the poorly developed wings and the yellowish coloration, and measures about 6 mm in length. Mean duration of the pupal stage is 5.7 days at 26°C, decreasing to 4.0 days at 30-32°C.
Adult. The adult is a brightly colored insect, measuring about 5-6 mm long. The head, legs, antennae, and ventral surfaces are bluish black. The thorax is reddish, and usually marked with two black dots. The elytra are highly variable in color. The tip and outer margin (leading edge) are orange, and the remainder is bluish black, but marked centrally with up to three yellowish white spots. The beetles are reluctant to fly when disturbed, usually dodging around to the opposite side of the stem. They also drop readily from the plant and feign death if they or the substrate are disturbed (Capinera, 1976). Adults are reported to overwinter in hollow asparagus stems, under debris in crop fields, and under loose bark of trees. (See color figures 4 and 104.)
The biology of asparagus beetle was given by Chittenden (1917) and Dingler (1934). Developmental biology was reported by Taylor and Harcourt (1978).
The larvae and adults feed on foliage during the summer months, reducing photosynthetic capacity of the plants and affecting subsequent crop yield. This damage is relatively infrequent, however, compared to direct damage by adults early in the season, when they feed directly on emerging asparagus spears. The pits and gouges caused by adult feeding render the spears of no commercial value. Adults also deposit eggs on spears, and on occasion eggs are serious contaminants because they cannot be removed by washing. Asparagus beetles are a regular problem in homegardens and on volunteer asparagus, and beetles may disperse to commercial crops occasionally. Because of the nature of the damage, growers in northern asparagus-producing areas consider asparagus beetle a serious threat.
Monitoring of adult populations is recommended early in the season. Visual observation is adequate. The distribution of all stages is clumped (Taylor and Harcourt, 1975).
Foliar insecticides can be applied to destroy adults and prevent egg laying on spears (McClanahan, 1975a). Spears are harvested almost daily, so use of an insecticide with little residual activity is essential. Beetles will often congregate on plants with an abundance of foliage, so it is advisable to leave a small portion of the crop as a decoy, while other areas are harvested. Destruction of volunteer plants, which often spring up along roadsides and irrigation ditches, can prevent population increases.
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