Liriomyza huidobrensis (serpentine leafminer)

Feeding punctures appear as white speckles between 0.13 and 0.15 mm in diameter. Oviposition punctures are smaller (0.05 mm) and are more uniformly round. The larva is primarily a leaf miner (on peas the larva may also feed on the outer surface of young pods); mines are usually white with dampened black and dried brown areas, and are usually associated with the midrib and lateral leaf veins. Mines are typically serpentine, of irregular shape, increasing in width as larvae mature; there should be no confusion with the mines of the European chrysanthemum leaf miner Chromatomyia syngenesiae which are less contorted and uniformly white. Several larvae feeding on a single leaf may produce a secondary 'blotch' mine type and leaf wilt may occur (Spencer, 1973).In potato, feeding punctures can often be seen all over the growing plant, giving the impression that a generalized outbreak of larval infestation is in process. But the development of the larval damage follows a rather fixed pattern, somewhat different from that of the adult fly population. First, the initial larval infestation and corresponding damage occur in the lower third of the plant, moving upwards to the top of the plant. At this time, practically the whole above ground part of the plant becomes necrotic and dies. Larval damage is consistently less severe during vegetative growth stages than when the plant is full grown. The occurrence of egg extrusion in the growing leaves might explain this phenomenon (Mujica and Cisneros, 1997).

Biological Control

Dacnusa sibirica is used as a biocontrol agent in glasshouses in Germany, but requires three to four releases per week (Leuprecht, 1992). In Dutch glasshouses, successful control was achieved using releases of D. sibirica in combination with Opius pallipes, in conjunction with the naturally present Diglyphus isaea (van der Linden, 1991). In Austria it was found that these parasitoids could be used in combination with cyromazine (Stolz and van Lenteren, 1996).

Control using nematodes can also be successful; Williams and Macdonald (1995) used foliar applications of Steinernema feltiae and species of Heterorhabditis (strain UK 211). Williams and Walters (2000) demonstrated that all three larval instars are equally susceptible to S. feltiae. Additional work was carried out to test the effects of some insecticides on the efficacy of S. feltiae; trichlorfon and dimethoate did not affect S. feltiae, but abamectin and deltamethrin reduced the nematodes ability to locate prey (Head et al., 2000).

Host-Plant Resistance

Some varieties of potato are resistant to Liriomyza attack (Valencia and Campos, 1980). Resistance in potatoes has be ascribed to the high density of glandular trichomes (Anon, 1993). Mou and Liu (2003) examined 46 lettuce genotypes for resistance to L. langei. Wild species had significantly fewer leafminer punctures as compared to cultivated lettuce. This suggests that genetic improvement of cultivated lettuce to produce resistant varieties is feasible.

L. huidobrensis is a serious pest of potato, vegetables and ornamental plants in the field and glasshouses in many parts of the world (Lange et al., 1957). In South America, it is a key pest of potato. In Europe and Mediterranean regions, L. huidobrensis is already a major pest of chrysanthemums, Primula spp., Verbena, lettuces (OEPP/EPPO, 1994), Phaseolus vulgaris, cucumbers, celery and Cucurbita pepo (ADAS, 1991). Treatments for chrysanthemums are recommended if 50 larvae are found in a random sample of the upper two-thirds of 10 stems (Spencer, 1982). Since it has spread to Mediterranean countries, it has appeared on outdoor crops, such as lettuce and sugarbeet (Echevarria et al., 1994). Although it initially proved to be a much more serious pest than L. trifolii in Israel (Weintraub and Horowitz, 1995), it has since come under natural biological control and is only occasionally a pest (Weintraub, 2001b).Damage is caused by larvae mining into leaves and petioles. The photosynthetic ability of the plants is often greatly reduced as the chlorophyll-containing cells are destroyed (Parrella and Bethke, 1984). Severely infested leaves may fall, exposing plant stems to wind action, and flower buds and developing fruit to scald (Musgrave et al., 1975). The presence of unsightly larval mines and adult punctures in the leaf palisade of ornamental plants can further reduce crop value (Smith et al., 1962; Musgrave et al., 1975). In young plants and seedlings, mining may cause considerable delay in plant development, leading to plant loss.