Opomyza florum F Yellow cereal fly

This pest is associated with cereals and grasses, and is often common. The larvae feed singly within the centre shoots. Infested shoots turn yellow and die; this typical 'dead-heart' symptom appears in the early spring at about the same time as damage caused by the larvae of wheat bulb fly, Delia coarctata (p. 197). If an infested shoot is removed from the leaf sheath, a characteristic spiral mark may be seen running down towards the base (Plate 7e). Early-sown winter wheat (i.e. crops drilled before mid-October) are most at risk but the larvae do not move from tiller to tiller; at least in the British Isles, this pest rarely causes significant damage.

BIOLOGY

Adults are active from mid-June onwards. Oviposition, however, does not take place until the autumn, when eggs are laid on the soil close to host plants. The eggs do not begin to hatch until late January or early February. Host plants are then invaded, a single larva feeding within the centre shoot and destroying the growing point. Larvae are fully grown in 5-6 weeks, usually by the end of May, and pupation occurs within the damaged shoots. Adults emerge about 3 weeks later. There is just one generation each year.

DESCRIPTION

Adult 2-4 mm long, yellow; wings clear, spotted with black. Egg 0.6 mm long, shiny white, spindle-shaped, with several longitudinal ridges and furrows. Larva up to 8 mm long, elongate and creamish-white (Plate 7f); no posterior papillae (cf. wheat bulb fly, Delia coarctata, p. 197); mandibles each with two large and three small pointed projections; anterior spiracles prominent, rosette-like but relatively small, usually 10-lobed (cf. frit fly, Oscinella frit, p. 195); posterior spiracles 3-pored and separated by a more or less distinct U-shaped depression (Fig. 255). Puparium 4 mm long, yellowish-brown, abruptly tapered anteriorly.

Fig. 255 Tip of abdomen of larva of yellow cereal fly, Opomyza fiorum: (a) posterior spiracle (further enlarged).
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