Liriomyza huidobrensis Blanchard Diptera Agromyzidae

Natural History

Distribution. Pea leafminer is widely distributed in South America, and seems likely to be native to that region. In the United States, it occurs west of the Rocky Mountains but is abundant principally in California (Spencer, 1981). Reports of infestations in eastern states apparently are based on misidentification. However, this leafminer is easily transported with cut flowers and vegetables, and there is concern that shipment of produce could result in establishment of this pest in eastern states. Pea leafminer has been introduced into Europe and Israel, where it is considered to be a very serious pest (Weintraub and Horowitz, 1995; 1996).

Host Plants. This insect is highly polyphagous, though as its common name suggests, garden pea is an especially suitable host. Plants from several families are attacked, including Chenopodiaceae, Compositae, Cruciferae, Cucurbitaceae, Leguminosae, Liliaceae, Linaceae, Solanaceae, Tropaeolaceae, Umbelliferae, and Violaceae. The vegetables known to be suitable hosts include bean, beet, broccoli, cabbage, cantaloupe, carrot, celery, Chinese cabbage, cucumber, eggplant, endive, faba bean, garlic, leek, lettuce, okra, onion, parsley, pea, pepper, potato, radicchio, radish, spinach, tomato, and turnip. Several flowers, including aster, baby's breath, chrysanthemum, dahlia, and zinnia are suitable hosts, as are numerous common weeds such as lambsquarters, Chenopodium album; and pigweed, Amaranthus spp. (Lange et al., 1957). (See color figure 7.)

Natural Enemies. As is the case with other Liriomyza species, numerous wasp parasitoids are known. Lange et al. (1957) reported Diglyphus intermedius (Girault), D. begini (Ashmead), Chrysocharis ainsliei Crawford, and C. parksi Crawford (all Hymenoptera: Eulophidae), Halticoptera sp. (Hymenoptera: Pteroma-lidae), and the braconid Opius sp. (Hymenoptera: Bra-conidae) from California. Parasitism was reported to reach 50-90% regularly. Insecticides interfere with parasitoids, especially Diglyphus. Pea leafminer has become a major pest of potatoes in Peru due to disruption of parasitoids by insecticides (Weintraub and Horowitz, 1995).

Life Cycle and Description. Pea leafminer completes its life cycle in 30-60 days, resulting in 5-6 generations per year depending on weather conditions.

  1. The white eggs are about 0.28 mm long and 0.15 mm wide, oval in shape, and inserted into foliage. Duration of the egg stage is about three (range 1.5-4.0) days. Females produce 8-14 eggs per day.
  2. The larvae feed in spongy mesophyll tissue and produce long, twisting mines that widen as the larvae mature. Although generally observed in leaves, mines may also be produced in stems and pods of peas. On leaves, the mine typically is initiated on the upper surface, but after feeding only a few millimeter the larva burrows to the lower leaf surface to complete its development. After passing through three instars, which normally requires 4-5 days but may take 10 days under cool conditions, the larva attains a length of about 4 mm.
  3. At maturity, the third instar normally cuts a slit in the leaf and drops to the ground to form a puparium in the soil. A fourth nonfeeding larval instar occurs before puparium formation, but this stage only persists for 4-5 h. The puparium measures 1.6-3.2 mm long, and is light-brown to almost black in color. The pupal stage lasts for about 7-13 days. There seems to be a relationship between puparium color and duration of the puparium; darker puparia have longer pupal periods.
  4. The small black and yellow flies measure 1.7-2.1 mm long. The wing length is 1.7-2.25 mm, considerably larger than American serpentine leafminer, Liriomyza trifolii (Burgess) (1.25-1.9 mm) and vegetable leafminer, L. sativae Blanchard (1.25-1.9 mm). The femora are dark or at least bear dark bands in pea leaf-miner, whereas in American serpentine and vegetable leafminer the femora are yellow. The adults live for
Liriomyza Huidobrensis

12-14 days, whereas females live considerably longer than males. During this time each female may produce up to 1000 leaf punctures using their ovipositor. About 80-90% of the punctures occur on the upper leaf surface. Generally, only 10-20% of the punctures, from which the females feed, also contain eggs.

Biological information was provided by Frick (1951), Lange et al. (1957), and Parrella and Bethke (1984). Weintraub and Horowitz (1995) provided a useful synopsis of history, biology, and management. Keys for the identification of agromyzid leafminers can be found in Spencer and Steyskal (1986).

Damage

Pea leafminer damage results principally from reduction in photosynthetic tissue caused by larval mining. Pea leafminer characteristically, but not exclusively, mines along the leaf midrib and lateral veins. It feeds within the spongy mesophyll tissue where chlor-oplasts are located. Thus, pea leafminer typically is more damaging than American serpentine leafminer, Liriomyza trifolii (Burgess), which burrows in the palisade mesophyll. However, larval feeding is not the only source of damage. Females puncture tissue with their ovipositor to create feeding sites, at which both females and males feed. The number of feeding punctures produced by females was estimated by Prado and Cruz (1986) at about 275 per day. These feeding punctures can be dense enough to cause leaf discoloration or deformity. In the case of crops where appearance is important, as in spinach, leaf punctures alone can result in rejection of a crop. Punctures, and especially mining, also make plants more susceptible to invasion by plant pathogens.

Management

  1. Weintraub and Horowitz (1996) suggested using yellow-sticky cards for leafminer sampling in potato, and demonstrated that highest catches occurred with traps placed at plant height. Heinze and Chaney (1995) evaluated leafminer sampling plans in celery.
  2. Pea leafminer management has not been extensively studied in the United States, probably owing to the restricted geographical distribution of the insect and susceptibility to insecticides. Parrella and Bethke (1984) suggested that L. huidobrensis is inherently more susceptible to insecticides than some other leafminer species, but that situation changed in the mid-1990s, when pea leafminer assumed greater importance to vegetable crops in California, presumably due to insecticide resistance. Also, about 1990 an insecticide-tolerant pea leafminer strain spread through many European countries, causing great loss to flower and vegetable crops in Europe and Israel.

Insecticides that are effective against larvae in the field generally have systemic properties. The neem-based botanical insecticides are effective when applied to the soil as a drench (Weintraub and Horowitz, 1997).

Cultural Practices. Alternatives to chemical insecticides are, as yet, few and relatively expensive. There has been some success in suppression of pea leafminer with entomopathogenic nematodes (Nematoda: Stei-nernematidae and Heterorhabditidae) if high humidity is maintained. Yellow plastic curtains coated with adhesive can be used to trap large numbers of flies. Some varieties of potato, particularly those with high densities of glandular trichomes, are somewhat resistant (Weintraub and Horowitz, 1995).

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