Tomato leaf miner
The tomato leaf miner is a small butterfly species from South America, which is a very difficult pest to control due to its hidden lifestyle and enormous reproduction potential. Since the moth mainly attacks tomatoes, where the feeding behavior of the larvae causes lasting damage to both leaves and fruits, it is classified as one of the most important pests of tomato crops.
Eggs: The laid eggs of the tomato leaf miner are cylindrical, 0.36 mm long and creamy white to yellow in color. Larval hatching begins as early as four to five days after egg laying.
Larvae: The tomato leaf miner moth goes through four larval stages during its development from egg to pupation. The larvae of the first larval stage are cream colored with a dark head capsule after hatching and are about 0.9 mm long. Larvae of the second through fourth larval stages are initially greenish, then slightly pinkish in color. The larvae of the fourth larval stage reach a length of 7.5 mm.
All larval stages have in common a dark shield in the anterior segment of the thoracic region (=prothoracic), directly behind the head capsule. In addition, as representatives of the butterflies, they have clearly recognizable pairs of legs. The development period from hatching to pupation is about 13 to 15 days.
Pupae: Pupation can occur in the soil, on the plant, in mine tunnels, in webs woven by the larva (cocoon), and also in the glasshouse structure or other objects (e.g., stored boxes). Pupal dormancy lasts nine to eleven days.
Adults: The adult moths are 6-8 mm in size and rather inconspicuous in color. The wings are silvery-gray in base color with characteristic dark spots in the forewings. The wingspan is 8-10 mm. Typical are the almost body-long, thread-like antennae, whose individual antennae links are strung like pearls.
Tuta absoluta is a leaf miner from the palp moth family (Gelechiidae) with a high reproductive rate (up to 260 eggs/female) which allows it to produce up to twelve generations per year.
The moths are nocturnal and hide among the leaves of plants during the day. The females lay their eggs freely on the leaves and stems of the host plants, but preferably on the underside of the leaves. The leaf miner requires a minimum temperature of 9 °C for its development. At 14 °C the development period is 76 days, at 27 °C only 24 days.
In glasshouses, the tomato leaf miner can overwinter in all stages of development. If there is sufficient food available for the larvae, they do not go through a diapause (=development dormancy).
After the larvae hatch from the eggs, they preferentially penetrate leaves. Further development takes place in the plant tissue, with characteristic patchy mine tunnels forming in the leaves as a result of feeding activity. The larva feeds only on the mesophyll (ground tissue) of the leaves, leaving the epidermis (outermost leaf layer) undamaged, making the feeding sites appear transparent.
Larvae can leave leaf mines and infest stems and fruit. If fruits are infested, yield and fruit quality can be significantly reduced - both by the direct (feeding) damage and by further colonization of the wounded plant organs with secondary pathogens. If stems and trunks are infested, malformations and growth inhibition occur on the plants.
Heavy infestation with T. absoluta leads to complete leaf death and can result in the total failure of a crop.
Possibilities of confusion
The following pests can be easily confused with the tomato leaf miner due to similar symptoms after infestation of the host plants, as well as appearance:
Leaf miners (Agromytidae, Diptera):
- The larvae of leaf miners also feed on leaves, but usually create serpentine mines inside the leaves. The mine passages of the tomato leaf miner moth are characteristically spot-shaped
- Unlike the tomato leaf miner moth, the larvae of leaf miners have no discernible pairs of legs or head capsule; they also remain whitish-creamy and do not change color until they pupate (barrel pupa)
Cotton bollworm(Helicoverpa armigera):
- The bores of both pests could be confused with each other, but those of the cotton bollworm have a much larger diameter of 5 to 10 mm (tomato leaf miner: 2 to 3 mm), in contrast to the tomato leaf miner moth
The main host plant of the tomato leaf miner is the tomato(Lycopersicon esculentum). However, damage has also been observed on other members of the Solanaceae family in cultivated, ornamental and various wild plants:
- Potato(Solanum tuberosum): damage only to aboveground parts of the plant, does not affect tubers.
- Melanzani(S. melongena): infestation under laboratory conditions
- Common datura(Datura stramonium)
- Wild tomato species: Lycopersicon hirsutum, L. peruvianum
- wild plants: S. lyratum, S. elaeagnifolium, S. puberulum, thorny datura(Datura ferox), blue-green tobacco(Nicotiana glauca)
- melon pear(S. muricatum)
- Black nightshade(S. nigrum)
Originally, the tomato leaf miner originates from South America, where it is considered the most important tomato pest in open field as well as in protected cultivation (foil tunnels and greenhouses). It has been known as a pest in large parts of South America since the early 1980s.
The first occurrence on the European continent was reported from Spain in 2006. In the 2007 growing season, massive yield losses were reported from all tomato growing areas in the coastal region. Since then, it spread very rapidly to countries in the Mediterranean region and North Africa, where it causes significant damage to tomato crops. In the meantime, occurrences are known in large parts of Europe as well as in parts of Africa and Asia. In Austria, the first occurrence was detected in Burgenland in 2010.
Propagation and transmission
According to a risk analysis of phytosanitary significance carried out in Holland, the highest risk of movement into a noninfested area is via the importation of tomato fruits including their packaging and transport material. In this process, all developmental stages of T. absoluta can be introduced. Tomato imports, especially from Spain, the Netherlands, Italy, and Morocco, thus pose a particularly high risk. The risk of movement from imports of tomato and melanzani plants, as well as ornamental plants from the Solanaceae family, is considered low. Under favorable conditions, the tomato leaf miner can spread naturally for several kilometers by drifting with wind.
In greenhouses, the likelihood of tomato leaf miner establishment is very high if a year-round crop of tomatoes or other host plants is managed and thus food for the pest is permanently available. In the open field, establishment is unlikely in our latitudes due to a relatively severe winter with frosts. However, a few generations can develop in the summer in an outdoor stand of tomatoes and host plants.
Prevention and control
- Immediate inspection of host and young plants for possible infestation when purchased
- Regular infestation checks in the crop
- Hygiene in and around the farms (remove plant material and weeds (especially from the nightshade family))
- No overwintering of host plants in glasshouses and removal of crop residues
- Use of insect nets on vents and in the entrance area of glasshouses
- Placement of pheromone traps with Tuta absoluta-specific attractant to detect early occurrence on the farm
- Removal and destruction of infested plant parts from the glasshouse
- Confusion method using pheromone, which overlays the sex attractants secreted by the females, resulting in the absence of reproduction
- Use of approved plant protection products with the indications tomato leaf miner, "biting insects" and leaf miners (see list of plant protection products approved in Austria)
- Use of Bacillus thuringiensis subsp. kurstaki
- Use of natural counterparts of T. absoluta - these are both parasitoids and predatory insects, such as the predatory bug(Macrolophus pygmaeus)
T. absoluta is not listed as a quarantine pest in the European Community, but is listed by the EPPO in the "A2 List of pests recommended for regulation as quarantine pests." list.
Last updated: 14.12.2021