There are three varieties of leafminer that that are generally capable of becoming a pest: the tomato leafminer (Liriomyza bryoniae), the florida leafminer (Liriomyza trifolii) and the grain leafminer (Liriomyza huidobrensis). Under natural conditions their larvae are kept under control by heavy parasitism from various species. But problems with leafminers have increased by the widespread use of broad-spectrum pesticides: their natural enemies are killed and the leafminers develop resistance against the scattergun use of these sprays.
Leafminers have the following observable development stages: the egg stage, three larval stages, a pupae stage and an adult stage. The adult leafminers are small, yellow with black markings flies. The larval miners burrow into the plant’s leaves. The pupation takes place underground.
Larvae literally ‘dig mines’ into the plant, which leads to the leaves drying out and falling off prematurely, as well as cosmetic damage. Losing leaves like this can also affect the plant’s yield. Feeding pinpricks made by female adults can lead to cosmetic damage too. Mould or bacteria can get into these dot-like wounds and go on to cause indirect damage.