Asparagus Miner
Ophiomyia simplex (Loew), Agromyzidae, DIPTERA


DESCRIPTION

Adult - The shiny black, slightly humpbacked fly is 2.5 to 3.5 mm long.

Egg - Inserted beneath the epidermis of an asparagus stalk, the egg is rarely seen. White at first, the 0.5 by 0.2-mm egg later assumes the color of asparagus tissues.

Larva - When newly hatched, the miner is pure white and about 0.4 mm long. The mature third instar has black rasping mouthparts and may be as long as 5 mm.

Puparium - The puparium is the shed skin of the last larval instar within which the pupa develops. Dark brown, flattened, and up to 4 mm long, the puparium has many hooks which attack it firmly to the plant.


BIOLOGY

Distribution - The asparagus miner has been reported to occur from southeastern Canada into Tennessee and North Carolina. It is also found in California, Hawaii, Europe, and Great Britain.

Host Plants - Asparagus and celery are the only known food plants of this insect.

Damage - Asparagus miners tunnel just below the surface of spears, usually near the base of plants. These insects were formerly believed to girdle plants causing yellowing of foliage and premature death. These symptoms are now attributed to the disease-causing fungus Fusarium. It has not yet been determined whether heavy miner infestations predispose plants to this disease. Miners cause some tissue breakdown (brown streaks) which may render spears unsalable, but they do not interfere with water or nutrient uptake and probably do not reduce yields. Seedlings and plants in newly set beds are most likely to become infested.

Life History - Biological studies on this insect have not been undertaken in North Carolina or other southern limits of its range. In New York, pupae within puparia overwinter in spears left in the field or 2.5 to 15 cm below the soil surface. Flies emerge the latter half of May and mate. One to two days later, oviposition begins. The flies live only 4 or 5 days and, therefore, produce only one batch of eggs. Eggs may be thrust into plant stems or deposited in the soil. After incubating 12 to 17 days, eggs hatch.

Larvae feed beneath the epidermis of the stem and develop through three instars in 2 to 3 weeks. Before pupating they usually mine toward the base of the plant. Pupation lasts 17 to 21 days and new adults usually emerge in July. The life cycle is then repeated except for the fact that the next generation of pupae overwinters. Only two generations are produced each year in New York.


CONTROL

Several wasps (Dacnusa rondani, Dacnusa bathyzona, Sphegigaster spp., and Pleurotropis epigonus) parasitize asparagus miner pupae and thereby help reduce populations. Cultural practices such as pulling and destroying spears at the end of the season or in early spring also do much to eliminate the overwintering stage of this pest. Chemical control of the asparagus miner is rarely necessary.

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