Napomyza carotae Spencer, 1966
Napomyza carotae is one of two small fly species feeding on carrots. The other, Psilia rosae L. (Diptera, Psilidae) belongs not to the family Agromyzidae and is, therefore, not a subject of this CD-ROM. The common name 'carrot fly' can be, therefore, misleading.
Both species can be distinguished among other characters by the larval feeding. Napomyza carotae always mines on the surface of the stems or the root of the plant, whereas Psilia is found deeper in the carrot.
IMPORTANT CHARACTERS
Wing length: 2.3 - 3.3 mm.
Diagnosis after Zlobin, 1994 a:
- orbital hairs usually in 2 irregular rows in front.
- third antennal segment moderately large, quadrate or round, with distinct but short pubescence.
- lower margin of epandrium tapering ventrally, without curvature Nap carotae ep.pct.
- basal part of distiphallus (mesophallus) relatively broad, equally wide in whole length Nap carotae aed, exp1.pct.
- neck of distiphallus usually strongly curved upwards Nap carotae aed, exp2.pct.
- broadened apex of distiphallus large.
- spermathecae semicircular / semispherical? Nap carotae sperm.pct.
Immature stages
Larval mouthparts similar to that of Napomyza lateralis with conspicuous lateral sclerites next to the mandibles. Puparium light brown.
HOST PLANTS
Apiaceae: The major crop plant is Daucus carota (carrot). Furthermore the following cultivated plants may be suitable to serve as host:
Pastinaca sativa (parsnip), Apium graveolens (celery), Petroselinum crispum (Miller) (parsley), Carum carvi L., Foeniculum vulgare (fennel).
Widespread weeds as Anthriscus sylvestris and Heracleum sphondylium or wild growing carrots and parsnip might also be able to maintain the population if no cultivated plants were available.
Choice experiments by Van 't Sant et al., 1975 with imagines revealed conflicting results: Adults reared from carrots were only able to infest Carum carvi (caraway) and the plant they came from.
BIONOMICS
The life cycle and behaviour of Napomyza carotae was studied in detail by Wiesmann, 1961, whom is followed here: The eggs were laid both into the stem and into the leaves, where also numerous feeding punctures can be found. After hatching the larva feeds its way through leaf veins, petioles, the stem and often at the end into the root. Pupariation takes place in the host plant, larvae from the root usually pupate near the base.
Van 't Sant et al., 1975 did not fully agree with Wiesmann, 1961 in stating that the larvae found in the roots normally come from the stem or other higher parts of the plant but rather hatch from eggs directly laid into the upper part of the carrot, which is exposed to the light. Hence, the agromyzids might be highly flexible in exploiting different parts of the host plant. They can finish their development in various plant parts depending on the growth stage of the plant and the population density of the mining flies.
Wiesmann, 1961 (in Switzerland) observed a relatively long larval development (53 - 68 days at 23 - 24°C) but a short pupal period lasting only 7 - 8 days. The first adults appear from the beginning of May, the last ones were found at the beginning of October. There are at least two, possibly three generations per year.
The females need an extraordinary preoviposition period of 4 - 5 days. During that time the females feed on plant sap obtained by puncturing the leaves.
DISTRIBUTION
Widespread in Europe, known from France, Finland, Germany, Great Britain, Hungary, Kirgyzstan, the Netherlands, Russia (European part, East Siberia), Sweden and Switzerland.
ECONOMIC IMPORTANCE
High infestation of carrots with Napomyza carotae is frequently observed in Europe, the species may be even more abundant than previously recorded. Because the feeding trace superficially resembles that of Psilia rosae L. (Diptera, Psilidae) the agromyzid fly presumably has been sometimes misidentified or overlooked (Spencer, 1973). Therefore the carrot mining fly must be considered as serious pest. A thorough evaluation of the yield reduction caused by this fly, however has not been undertaken. Larval feeding within the root is normally restricted to the upper part near the stem. Since the mines are superficially they are not destroying the carrots completely, they are still suitable for human consumption. On the other hand the overall vigor of the plant can be affected by larval feeding in the petioles and the stem.