Pegomya hyoscyami Panzer Mangold fly

This is a widespread and common but usually minor pest of mangold and sugar beet; infestations also occur on red beet and spinach. The larvae (known as 'beet leaf miners') feed within large blotch mines. Mined leaves appear scorched and may eventually decay; this affects the marketable quality of spinach plants. Growth of plants, however, is rarely affected significantly unless heavy infestations occur on young plants. Crops are usually at greatest risk from firstgeneration attacks; sugar beet crops are more likely to suffer significant damage where crops are drilled to a stand.

BIOLOGY

Adults appear in early spring and deposit their eggs in small batches on the underside of host leaves. The eggs hatch in about 5 days. The larvae then burrow directly into the leaf tissue. They feed gregariously for about 2 weeks and form large, brown blotch mines, each of which commences as a linear gallery. Fully grown larvae enter the soil to pupate, and a second generation of adults emerges in July. In favourable areas and seasons, a third generation of adults appears from late August to early September.

DESCRIPTION

Adult 5-6 mm long; thorax mainly greyish-brown; abdomen reddish-brown; legs yellow with black tarsi. Egg 0.8 mm long, broadly elongate, white; chorion reticulate. Larva up to 8 mm long, greenish-white to yellowish-white (Plate 10b); anterior spiracles 8-lobed, fan-like; posterior spiracles relatively small, surrounded by numerous prominent papillae (cf. spinach stem fly, Delia echinata, p. 198). Puparium 6-7mm long, dark reddish-brown, barrel-shaped; posterior spiracles prominent (Fig. 268).

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