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Liriromyza huidobrensis Blanchard (Diptera: Agromyzidae)

Synonyms: Agromyza huidobrensis Blanchard

Liriomyza cucumifoliae Blanchard

Liriomyza langei Frick

Liriomyza dianthi Frick

Common names: Serpentine leaf miner, pea leaf miner, South American leaf miner, South American miner fly (English), Südamerikanische Minierfliege (German), Mosca minadora, Minadora sudamericana (Español), Mouche mineuse sud-américaine (French), Mosca minatrice sudamericana (Italian), Larva mineira sul-americana (Portuguese)

Hosts

Fourteen families of plants have been recorded as hosts, without a clear preference for any particular family. L. huidobrensis has been reported from Amaranthus spp., Aster spp., aubergine (Solanum melongena), beet (Beta vulgaris), red pepper (Capsicum annuum), celery (Apium graveolens), chrysanthemum (Dendranthema morifolium), cucumber (Cucumis sativus), Dahlia spp., Dianthus spp., faba bean (Vicia faba), garlic (Allium sativum), Gypsophila spp., hemp (Cannabis sativa), Lathyrus spp., lettuce (Lactuca sativa), lucerne (Medicago sativa), melon (Cucumis melo), onion (Allium cepa), pea (Pisum sativum), common bean (Phaseolus vulgaris), potato (Solanum tuberosum), Primula spp., radish (Raphanus sativus), spinach (Spinacia oleracea), tomato (Lycopersicon esculentum), Tropaeolum spp., Verbena spp. and Zinnia spp.

Symptoms

Haulm: Newly hatched larvae feed under the leaf epidermis mainly close to the leaf midrib creating characteristic serpentine mines the diameter of which increases as larvae grow. Affected leaf tissue becomes necrotic and brownish. Older leaves at the lower plant part show the first damage. Middle and upper leaves are progressively damaged as the plant develops and infestation continues. As necrotic areas coalesce in highly infested leaves, the leaves dry out and die. Accordingly, highly infested potato fields appear burned.

Status of the pest

L. huidobrensis is a destructive, polyphagous insect pest in the tropics and subtropics. It  has been reported from Peru, Chile, Argentina, Brazil, Central American countries, Mexico, Northern Africa, Kenya, Indonesia, Malaysia and Israel. The leafminer fly has become a key pest in all countries where it has been unintentionally introduced, capable of completely destroying potato fields if no control is applied. In many regions, leafminer flies have become resistant to commonly used insecticides (e.g. carbamate, organophosphate and pyrethroid) that are used to control larvae and adults. Potato farmers in the coastal valleys of Peru try to control the pest by 8-13 calendar sprayings per season. Therefore, insecticides often present the highest input costs in potato production. Without control, yields are commonly reduced by 50%. Most of the leafminer fly research of the past 20 years has been oriented to find new chemical compounds to replace those insecticides that have lost their efficacy for controlling the pest. In this context, the surge of leaminer fly as a pest has been attributed to the destruction of its natural enemies. Therefore, alternative control methods have been investigated, including the evaluation and development of tolerant potato varieties, the role and use of natural enemies, cultural practices, trapping devices, and the selective application of larvicides. These control tools combined with monitoring of the fly population are today the basis for developing integrated pest management strategies for this pest.

Life cycle and biology

A leafminer fly has four life stages: egg, larva, pupa and adult. Adults are small (1.7-2.3 mm), black flies with bright yellow spots on the thorax, with females being slightly larger than males. Peak emergence of adults occurs before midday and males usually emerge before females. Mating and oviposition occurs after 6-24 hours and over a period of 1-3 days, respectively. A single mating is sufficient to fertilize all the eggs. Females use the ovipositor to make holes, so called “feeding punctures”, in the top and/or bottom of leaves, promoting the production of exudates that will feed both males and females. The amount of leaf stippling varies between plant species, with 83 (in aster) to 277 (in bean) punctures per day reported. Wounds prepared for egg laying are called “oviposition punctures”. On average, females lay 8-14 eggs per day, which are inserted just below the leaf surface. Eggs are round and translucent about 0.3 x 0.1 mm. At lower temperatures oviposition is increased; 18ºC being the best temperature for development. Larvae hatch within 2-5 days according to temperature and start feeding in the spongy mesophyll of the leaf. Larvae develop in three distinguishable larvae stages (4-10 days) that can be recognized by the length and thickness of the leaf mine. The third-instar larva measures 3.2 x 1 mm. Mouth hooks remaining in the mines after each successive molt can be used for stage identification. Due to their mining habits larvae reduce the plant photosynthetic ability that causes the main damage. Leafminer fly pupae develop either on the plant foliage or just beneath the soil surface. Pupae vary in size (1.6-3.25 mm long, 0.7-1.1 mm wide) and color (light brown to almost black). Adult emerge 7-17 days after pupal development. With a life cycle of only 2-5 weeks, up to 15 generations per year may develop.