Ophiomyia simplex Loew Diptera Agromyzidae

Natural History

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.

  1. The female deposits eggs beneath the epidermis of stems, usually near the base of the plant. The presence of the egg in the plant tissue is not apparent. The egg is white, and elongate oval. One end tends to be more pointed than the other. The egg measures about 0.48 mm long and 0.22 mm wide. Duration of the egg stage is estimated to be 7-14 days.
  2. The larva is whitish. It tapers slightly at both ends, and the anterior end bears black mouth-hooks, while the posterior end bears a pair of black spiracles. There are three instars, and their length is
Ophiomyia Eggs

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.

  1. Pupation occurs within the larval mine. First-generation larvae usually pupate above-ground, whereas second-generation insect tend to pupate in the stalk or roots below-ground, often at a depth of 5 cm or more. The puparium initially is light-brown, becoming dark brown with age. It is somewhat flattened in form, and measures about 4-5 mm long. The puparium bears hooks at both ends. Duration of the pupal stage is 14-21 days during the summer, and several months during the winter.
  2. The adult is shiny black in appearance. It measures 3-4 mm long, with a wing span of 5-6 mm. The wings are colorless. Fecundity is unknown.

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.

Damage

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.

Management

  1. Lampert et al. (1984) suggested that the pupal stage, particularly autumn puparia, was the best sampling unit. They also presented information on optimal sample size for fly populations with different densities. Ferro and Suchak (1980) studied methods of adult sampling and recommended yellow or lime green sticky stakes because of the relatively large number of flies captured with these techniques.
  2. Insecticides applied to the stems of asparagus plants reduced abundance of asparagus miners and incidence of crown rot disease, and increased crop yield (Damicone et al., 1987). Soil fumigation also enhances yield due primarily to destruction of fungi, but this approach is very expensive and useful only for the plant establishment phase of asparagus production.

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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