The carrot fly is a widespread and important pest of carrot, celeriac, celery, parsley and parsnip; several wild species of Umbelliferae (but not all) are also hosts. Carrot: roots of plants of all ages are affected. Seedlings are often killed; this causes noticeable gaps in crop rows and increases the likely severity of attacks on surviving plants later in the season. Infestations on young plants cause the foliage to turn reddish, wilt and die; superficial damage by larvae can cause root fanging and stunting of plants. On older plants, larvae mine the outer tissue of the tap root; the cortex then becomes riddled with brown or rusty-red tunnels (cf. damage caused by carrot miner, Napomyza carotae, p. 189); the extent of damage increases throughout the late summer and autumn, and will also continue in clamps throughout the winter. Mined roots are susceptible to canker and subsequent rotting. Celery: damage to fibrous roots causes the outer leaves to wilt; more seriously, mining in the base of leaf stalks, crown and main roots results in poor top growth and yellowing of the foliage. Early-season transplants are particularly liable to be attacked, and damage affects the size and overall quality of plants. Parsley: larvae mine the outer tissue of the tap root and also destroy the fibrous roots; this affects plant vigour and quality. Parsnip: the main roots of young plants are often severed, and the larvae also burrow within the petioles; on older plants, mining is restricted mainly to the region of the tap root in the top 15 cm of soil.
Adults of the first generation appear in May or June, and eggs are deposited singly or in small groups in the soil close to host plants. They hatch in about a week. The larvae then attack the fibrous roots and also graze on the surface of the tap root. Some second-instar larvae mine within the tap root but most internal feeding occurs during the third (= final) instar. When fully grown, the larvae return to the soil to pupate, and adults of the second generation emerge from late July or early August onwards. Second-generation larvae usually complete their development in the autumn, but many will continue to feed well into the winter before eventually pupating. Under favourable conditions a third or partial third generation of adults appears in the autumn; thus, adults may occur at any time from May to October or November. Depending on temperature, the precise timing of adult appearance and the duration of the immature stages vary considerably from site to site and from year to year.
Adult 5-7 mm long, shiny black; head reddish-brown; legs yellowish (Fig. 252); antennae with the bulbous third segment half yellow and half black (Fig. 253a) (cf. Psila nigricornis, 182); wings 5.5 mm long, large and iridescent. Egg 1.0 x 0.4 mm, white, ribbed longitudinally. Larva up to 10 mm long, shiny creamish-white, slender-bodied (Plate 7b); mouth-hooks with their long axis more or less continuous with the rest of the mouthparts, and each with one
tooth; posterior spiracles distinctly pigmented and 3-pored (cf. Napomyza carotae, p. 189). Puparium 5-7 mm long; elongate, yellowish-brown.
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