Damage. The leaf miners are a group of small flies, the larvae of which can do serious damage to horticultural crops by tunnelling through the leaf. This species is found on members of the plant family Asteraceae. Plants attacked include chrysanthemum, cineraria and lettuce.
Life cycle. The flies emerge at any time of the year in greenhouses, but normally only between July and October outdoors. These adults, which measure about 2 mm in length and are grey-black with yellow underparts, fly around with short hopping movements. The female lays about 75 minute eggs singly inside the leaves, causing white spot symptoms to appear on the upper leaf surface. The larva stage is greenish white in colour, and tunnels into the pal-lisade mesophyll of the leaf, leaving behind the characteristic mines seen in Figure 14.17. On reaching its final instar, the 3.5 mm long larva develops within the mine into a brown pupa, from which the adult emerges. The total life cycle period takes about three weeks during the summer months.
Amateur gardeners have no effective insecticide product to control the larva inside the leaf.
Professional growers use tiny wasps such as Diglyphus isaea and Dacnusa sibirica to parasitize the tunnelling leaf-miner larvae. Products containing abamectin may be used outdoors and in greenhouses. (The occurrence of South American leaf miner (Liriomyza huidobrensis) and American serpentine leaf miner (Liriomyza trifolii) which are able to damage a wide variety of greenhouse plants has, in recent years, created many problems for horticulture).
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