The turnip moth is a major pest of vegetable crops such as carrot, leek, lettuce, onion, parsnip, potato, red beet and turnip; it is also a minor problem on cereals, strawberry and various ornamental plants. The larvae damage plants at or about soil level, often causing them to wilt and die. Attacks are particularly severe in light soil during hot, dry summers and tend to be most significant on younger, unirrigated, slower-growing hosts, including seedlings and recent transplants. Carrot, red beet and other root vegetables: larvae hollow out large cavities in the tap root, destroying roots or reducing their marketability. Leek: attacked plants develop distorted top-growth, and the stems become characteristically twisted. Lettuce: plants are very susceptible to damage, often being cut off at ground level or
their stems partially severed; recent transplants and seedlings are worst affected. Potato: roots and stems are severed and tubers hollowed out (Plate 14e); the most significant damage is caused before July.
Adults fly from late May to June or early July. Eggs are laid in batches on the leaves of various host plants and hatch within approximately 3 weeks. Young larvae feed on the leaves but, on attaining the third instar, they become subterranean and act as typical 'cutworms'. They are active at night but, during the daytime, may be found resting in the soil close to plant roots. Most larvae are fully fed by the autumn. They then overwinter and pupate in the spring, each in an earthen cell. Under favourable conditions, however, some larvae will pupate before overwintering to produce a partial second generation of adults in the autumn. Survival of this species is greatly hampered by rainfall during the critical early stages of larval development.
Adult 38-44 mm wingspan; forewings whitish-brown with brownish-black or blackish-edged markings, including a basal dash and two subcentral stigmata (Fig. 316a); hindwings
pearly-white; antennae of male bipectinate (Fig. 317a). Egg 0.6mm diameter, pale grey to creamish, hemispherical and distinctly ribbed. Larva up to 35 mm long; body plump; glossy greyish-brown, with a yellowish or pinkish tinge and indistinct darkish lines along the back; pinacula black; head yellowish-brown; adfrontal plates blunt at apex (Fig. 318a) (cf. Agrotis exclamationis, p. 236); mandibles elongate (cf.
A. vestigialis, below); spiracles black. Pupa 1820mm long, reddish-brown and glossy; cremaster with two divergent spines.
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