Phytomyza syngenesiae Hardy larva A chrysanthemum leaf miner

Infestations of this leaf miner (widely known in older literature as 'Phytomyza atricornisl see also under P. horticola, p. 193) are often established on various members of the Asteraceae, especially glasshouse crops such as chrysanthemum; severe infestations are also reported on lettuce. The whitish to brownish larval mines are disfiguring and, if several occur on the same leaf, infested leaves may wilt, turn brown and die. Adult leaf-feeding punctures, which sometimes develop from small, whitish spots to brownish warts, are also disfiguring. Although usually regarded as a pest, the insect has been tested in New Zealand as a potential biological control agent for use against the weed Senecio jacobaea.

BIOLOGY

Adult females deposit eggs singly through punctures made in the upper surface of leaves. The eggs hatch a few days later. The larvae then mine within the leaves to form long, winding, narrow, wavy-edged (cf. American serpentine leaf miner, Liriomyza trifolii, p. 189) galleries, clearly visible from above. Black pellets of frass are deposited irregularly to one side along the length of the mine. Larvae as usually fully fed after 7-10 days. Each then burrows to the lower surface of the leaf to pupate in a small chamber, with the anterior spiracles of the puparium protruding through the lower epidermis (cf. Phytomyza horticola, p. 193, and Liriomyza trifolii, p. 189). Adult flies emerge one or more weeks later. The duration of the various stages depends on temperature, and breeding in glasshouses is continuous if conditions remain favourable, e.g. where all-year-round (AYR) chrysanthemums are grown. On outdoor hosts, there are usually two generations annually.

DESCRIPTION

Adult greyish-black, faintly marked with pale yellow on the head and sides; legs mainly black, with pale yellow knees; wings 2.2-2.6 mm long. Larva up to 3.5 mm long, greenish-white; mouth-hooks set more or less at right-angles to

Phytomyza Horticola

rest of mouthparts, and each with two prominent teeth; posterior spiracles each with 8-10 pores (cf. American serpentine leaf miner, Liriomyza trifolii, p. 189). Puparium 3 mm long, yellowish-brown to dark brown, slightly flattened (Fig. 261).

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