It is important to differentiate leafmining flies and leafmining caterpillars, since the management of the two groups of pests is different.
(The leafminers attacking coffee, cotton, groundnut, soybean and citrus are caterpillars, not leafmining flies. They are described under their respective crop).
Here we describe the leafmining flies:
Major species of leafmining flies in Africa are:
- The serpentine leaf miner ( Liriomyza trifolii)
- The vegetable leaf miner (L. sativae)
- The cabbage leaf miner (L. brassicae)
- The pea leaf miner (L. huidobrensis)
Leafmining flies are serious pests of vegetables and ornamental plants worldwide. They are occasional pests of brassicas. Liriomyza brassicae is cosmopolitan. In Africa it is reported from Egypt, Ethiopia, Kenya, Mozambique, Zimbabwe, Cape Verde and Senegal. Host plants are primarily crucifers.
Two species of serpentine leafmining fly, L. trifolii and L. sativae, are considered serious pests of tomatoes. Both species are cosmopolitan. Liriomyza sativae is a typical American pest, whereas the typical leafmining fly in Europe is L. bryoniae. Liriomyza trifolii is common on tomato in America and Europe, and L. huidobrensis is occasionally reported on tomato in America but damage has been recorded mainly on ornamentals. Leafmining flies L. trifolii and L. sativae are closely related with similar appearance and overlapping host ranges.
In Africa, L. trifolii has been reported in several countries, including Kenya, Mauritius, Reunion, Senegal, South Africa and Tanzania. In Kenya, Liriomyza trifolii was introduced to Kenya in the late 1970s through chrysanthemum cuttings from Florida (USA). Since then, Liriomyza species have been found throughout the country, attacking vegetables and ornamental plants. Liriomyza. huidobrensis is currently a serious pest of ornamentals and passion fruits. Liriomyza sativae was recently recorded in Kenya.
L. brassicae has also been reported for many years as a pest on brassicas and legumes, but in general, the damage done to mature crops is largely superficial.
Female leafmining flies puncture leaves and in some instances also fruits/pods (e.g. peas) with their ovipositor to feed and to lay eggs. These punctures can serve as entry point for disease-causing bacteria and fungi, but in most cases they are not of economic importance. However, they can be a problem for export products such as on snow-peas and ornamentals. Eggs are laid inside the plant tissue, and they cannot be removed through washing; this may lead to rejection of the produce when their presence is detected during import inspection.
|Leaf of okra seedling showing attack by leaf mining flies. Note pupa (yellow colour) on leaf.
|(c) A.M.Varela, icipe
Damage by maggots feeding in the plant tissue is economically more important than the feeding punctures of adult flies. Maggots feed between the upper and lower surface of the leaf making tunnels or mines as they move along. Although individual mines on leaves do not produce much damage, heavy attacks, especially on seedlings, may result in dying off of young plants. Heavy attack leads to large-scalenecrosis of leaf tissue, eventual shrivelling of the whole leaf and may result in complete defoliation of crops. Defoliation of tomato plants may also expose fruits to sunburn and thus affect their market value.
|Leafmining flies damage on tomato leaf. Note maggot ready to pupate (yellow) and pupa (brown). A. M. Varela, icipe.jpg
|(c) A. M. Varela, icipe
Heavy infestation reduces the photosynthetic capacity of the plant and affects the development of flowers and fruits. However, mature plants of most crops such as tomato and cabbage can withstand considerable leaf mining, especially on the lower or outer leaves. In other crops, where feeding occurs on the marketable part of the crop, even slight damage may lead to rejection of the crop. This is particularly important for export crops, as most Liriomyza species are considered quarantine pests in the EU and there have been rejections of produce exported to Europe.
Leaf miners are able to colonise a wide range of plants (primarily although not exclusively Solanaceae, Leguminosae and Asteraceae). Liriomyza flies have become important pests of horticultural crops and potatoes in the tropics and subtropics. The most common species, L. sativae, L. trifolii and L. huidobrensis, feed on a wide range of plants. Main host plants include cabbage and other brassicas (cruciferous crops), okra, onion, pigeon pea, bell pepper, cucumber, pumpkin, cowpea, potato, passion fruit, tomato and common bean.
In East Africa, these leaf mining flies are recorded from most export vegetables with sometimes extremely heavy damage on French and runner beans, citrus okra, eggplant, passion fruit and peas. Severe infestations have also been recorded on cut flowers. Liriomyza brassica attacks mainly crucifers. It has no economic importance in the region.
Affected plant stages
Seedling and vegetative growing, flowering and fruiting stages.
Affected plant parts
Leaves and pods.
Symptoms by affected plant part
Feeding and egg-laying by female flies result in white puncture marks on leaves. These punctures are easily seen and are the first signs of attack.
Feeding by maggots leaves irregular mines on the leaves, with occasional thread-like black frass inside the mine. Severely mined leaves may turn yellow, disfigured, and drop.