Geomyza tripunctata Fallen Grass cereal fly

This widely distributed fly is associated mainly with rye-grass and certain other grasses but will also attack wheat. The larvae feed within the central shoots that then turn yellow and die ('dead-heart' symptom). Infestations, however, do not reach economic levels.


Adults occur at any time from early March to November, but are usually most numerous in April and again from July to October. Eggs are deposited singly on the stems of host plants, usually at or just below soil level. After egg hatch, the larva bores into the base of a leaf and then burrows spirally downwards to enter the base of the central shoot, within which further development takes place. Larvae eventually pupate in the soil and adults emerge 17-30 days later. There are normally two generations annually. The winter is usually passed in the final (third) larval instar, such individuals then pupating in February or March.


Adult 2.5-3.5 mm long, greyish-black. Egg lmm long, spindle-shaped, shiny white, with numerous irregular longitudinal furrows and ridges. Larva up to 6.5 mm long; body plump, greyish-white and opaque (Plate 7c); anterior spiracles elongate, each with up to 16 lobes;

Fig. 254 Puparium of grass & cereal fly, Geomyza tripunctata (x1O).

posterior spiracles 3-pored and borne on short tubercles. Puparium 4 mm long, dark reddish-brown, elongate and obliquely truncated anteriorly (Plate 7d); anterior spiracles very prominent (Fig. 254).

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