Distribution. This fly is native to Europe, where it occurs widely. It was first noticed in North America about 1861, and probably was introduced with asparagus plants. By the late 1800s and early 1900s it was found generally in New England and the Middle Atlantic States, and had been distributed to some locations on the Great Lake States. The asparagus miner was detected in California in 1905. It is now believed to occur wherever asparagus is grown.
Host Plants. Asparagus miner has a very restricted host range, feeding only on asparagus. It is rarely associated with asparagus spears (young shoots); instead, it is normally found principally on older stalks bearing "ferns." Asparagus miner attacks young plants, however, if they are old enough to bear ferns.
Natural Enemies. Little is known about the natural enemies of asparagus miner in North America. One parasitoid, Chorebus rondanii (Giard) (Hymenop-tera: Braconidae), is known from Massachusetts, and also is found in Europe (Krombein et al., 1979). Barnes (1937a) noted other parasitoid species in England which apparently have not been introduced to North America.
Life Cycle and Description. There are two generations annually throughout the range of this insect, with the pupal stage overwintering. The adults first become apparent in May, and within a few days of emergence they copulate and begin oviposition. First generation larvae are common in June, completing their development and pupating in July. By late July or early August, second generation adults have emerged and begin producing eggs. Second generation larvae begin to mature in late August and early September. The larvae form puparia in the autumn, remaining in diapause until April or May of the following year.
about 0.4, 2.0, and 3.5 mm, respectively, during instars 1-3. Barnes (1937a) gave characters to separate the instars. Duration of the larval stage has been poorly documented, but it seems to be 7-14 days.
The biology of the flies was given by Fink (1913) for New York, and Barnes (1937a) for England. Ferro and Gilbertson (1982) and Lampert etal. (1984) provided bionomics in Massachusetts and Michigan, respectively.
The larvae feed just beneath the surface of the stem, interfering with photosynthesis. Burrowing starts at about soil level and proceeds upwards, forming mines. If several larvae are present in the same stalk the feeding activity of the larvae will girdle the plant. Infested plants become yellow in color. Discoloration may occur only at the base when few flies are present, or the entire plant may be affected. Burrowing by larvae also extends downward and even includes feeding on the roots. Larvae do not seem to damage young spears. The flies do not readily oviposit on this young tissue, and if they do, the eggs and larvae are too small to be observed at harvest, so they are not culled.
The importance of asparagus leaf miner has been disputed. Eichmann (1943), for example, dismissed the possibility of injury, including the potential of interaction with crown rot disease caused by Fusarium spp. Although the direct effects of asparagus miner on yield are likely minimal, it is now apparent that their involvement with disease is significant. The fungi Fusarium moniliforme and F. oxysporum are associated with all life stages of asparagus leaf miner, and increased incidence of Fusarium is associated with stem mining. Commercial asparagus fields in Massachusetts were found by Gilbertson et al. (1985) to harbor 1.9 mines per stem and 2.9 pupae per stem. Significant decline in commercial aspragus in northeastern states has been attributed to the Fusarium and asparagus miner problem.
Cultural Practices. Destruction of overwintering stalks is sometimes recommended because puparia are harbored in the stalks. However, this is not completely satisfactory because some flies are associated with the roots. Wild asparagus is a major source of flies, and roadsides and irrigation ditches that might harbor asparagus should be checked for plants, and efforts made to eradicate them.
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