# Tomato leaf mines: distinguish Tuta absoluta and fly leafminers URL: https://leafwrit.com/mt/tomato-pest-management/ Reviewed: 2026-10-29 ## Tomato pesticides: sort the damage before choosing a treatment Identify the damaged tissue and the pest before choosing a treatment. Cutworms chew irregular surface holes in fruit near the ground. Flea beetles may feed beneath the calyx of ripe fruit, while pinworms enter through it and feed inside. Photograph the stalk attachment and the lower surface before cutting the fruit open. ## Natural pest control for tomatoes: start with diagnosis and non-chemical methods Natural pesticides for tomatoes, including any organic pesticide for tomatoes, are covered in the [organic crop-protection guide](/mt/organic-pesticide-checks/). For any organic product, get the complete formulation and the proposed crop use, and ask your organic control body to assess it. Physical, mechanical and biological interventions come before chemical treatment to avoid crop losses, so match that sequence to the diagnosed pest and the crop’s present condition. ## Best insecticide for Tuta absoluta in tomatoes: find the larva first Before choosing an insecticide, confirm the larva and gather the crop history. A manufacturer’s Tuta absoluta offer, such as one from Syngenta, is checked like any other product: ask for the full commercial name and authorisation number and match them in the Maltese register. If a supplier offers an abamectin product, ask for its full commercial identity and the Maltese conditions of use. If they speak of “tomato pinworm”, ask which species they mean. Tomato pinworms enter fruit through the calyx and tunnel inside. Tuta absoluta is also known as Phthorimaea absoluta, the current taxonomic name, with EPPO code GNORAB. Larvae mine leaves and bore into fruit and stems. Write both names in your notes so older crop documents can be matched. Larvae feed within the mesophyll, creating irregular mines while leaving the leaf epidermis intact. Mines later turn necrotic. Look for black frass and larvae inside the affected tissue. Larvae enter developing tomato fruit and tunnel into stems. Fruit galleries admit secondary pathogens, contributing to decay, so check fruit and stems as well as leaf mines. Tomato plants are attacked from seedlings through maturity. Inspect apical buds, flowers and new fruit as well as leaves, and note the crop stage with each finding. Use sex-pheromone traps to monitor adult moth activity. Record trap catches separately from leaf mines, living larvae and damaged fruit, and compare them over the same period. Tomato is the main host; related cultivated and wild solanaceous plants also host the pest. Rotate with non-solanaceous crops, remove infested plants and manage post-harvest debris to reduce carryover. Plants for planting and tomato fruit can carry the pest, so record incoming lots and movements of crop material when you trace an infestation. For a suspected potato borer, distinguish foliage, stem and tuber damage. Tuta absoluta attacks aerial potato parts but does not develop in tubers, so look for another cause of tuber galleries. Adults are nocturnal and commonly hide among foliage by day, so check traps as well as daytime observations. ## Crop pest identification in Malta: tomato and potato symptoms and reporting Tuta absoluta reached Malta in April 2009, when it was found in a greenhouse in Dingli, in the south-west. The national plant protection organisation started monitoring surveys to follow its spread. The pest is now present in most tomato-growing regions of both Malta and Gozo. EPPO, evaluating information dated 2022, lists it in Malta as present with restricted distribution. A mined tomato leaf on a Maltese holding is therefore a likely Tuta absoluta find, and it still needs to be confirmed on the larva. On potato, Tuta absoluta attacks the aerial parts of potato and does not develop in tubers, so tuber galleries point to another pest. ## Pesticide resistance planning: modes of action and a useful failure investigation When a treatment fails, review the pest identification, the application history and the label conditions. Separate inherited resistance from an unreachable feeding site or poor delivery. Resistance is an inherited change in pest sensitivity causing repeated failure of expected control under the label’s conditions for that pest. Look at identification, delivery and application records together with repeated field results. Initially rare resistant individuals survive exposure and pass resistance traits to offspring. Repeated use of the same mode of action selects these survivors as susceptible individuals are removed. Compare the mode-of-action history across successive pest generations. The IRAC classification gives each active ingredient its mode-of-action group and chemical class. Write both beside the commercial name when you compare treatments. Cross-resistance allows resistance to one insecticide to confer resistance to another, including an unexposed product. Metabolic mechanisms can produce cross-resistance across groups, so check these links before choosing an alternative. Resistance-management programmes alternate, sequence or rotate different mode-of-action groups, with spray windows aligned to crop development and pest biology. Time them for the pest generations present in the crop. Resistance can increase rapidly in greenhouses where pests reproduce quickly, susceptible immigration is limited and treatments are frequent. When failures repeat, review crop overlap and the treatment sequence. Use the IRAC Mode of Action Classification Scheme, version 11.5, February 2026, to classify insecticides and acaricides. Selective nematicides have a separate classification. Match the group to the active ingredient in the proposed formulation. Abamectin and emamectin benzoate share IRAC group 6, the glutamate-gated chloride-channel allosteric modulators. Spinosad and spinetoram share group 5, acting at nicotinic acetylcholine receptors. Pyrethrins and synthetic pyrethroids belong together in subgroup 3A, the sodium-channel modulators. Switching within any of these groups retains its mode of action. Check current Maltese authorisation and the crop label separately from the mode-of-action group: the group says how a substance acts, while your field records show how it performed against your population. ## Before choosing the best insecticide for leaf miners: examine the living stage To choose a pesticide for a leaf miner in tomato, open the mine and look for the living larva. Send an intact leaf and the crop history with any identification enquiry. The best pesticide for a leaf miner in tomato is preceded by prevention: transplants are examined for leafminers and mines before planting, and old plantings are removed after harvest to reduce early infestations in the next crop. Record incoming plant material and the overlap between successive crops. Parasitoids attack leafminer larvae. Broad-spectrum insecticides used against other pests disrupt this control, so when leafminers increase, review the whole crop’s treatment history. Liriomyza leafminers are flies. Females insert eggs into leaves, and larvae feed between the surfaces, leaving winding tracks. Mature larvae leave mines and drop to the ground to pupate. Record occupied mines, empty tracks and pupae under the plants separately. Liriomyza sativae and L. trifolii have similar yellowish maggots and brown, seedlike pupae. Adult head colour and thoracic appearance help distinguish them. Careless handling or alcohol removes the silvery appearance used in identifying one species. Confirm the specimen-preservation instructions before you collect adults. Photograph an intact leaf as well as the damage: a winding internal mine, a surface pit, an irregular perforation and a missing leaf edge are different observations. Include the insect where you found it, and label cotyledons, first true leaves, older leaves and growing points separately. ### Read the adult leafminer’s head and thorax Adult leafminers are small black-and-yellow flies. Liriomyza sativae has a shiny black upper surface with a yellow triangle between the wing bases. Its face and underside are yellow. L. trifolii has overlapping thoracic bristles that give a fresh specimen a silvery-grey appearance. Behind the eyes, L. trifolii is mostly yellow, with a small black area against the eye’s rear edge. L. sativae is predominantly black in that position. Photograph the thorax before handling changes its appearance. Heavy mining produces whitish blotches and premature leaf drop. Early defoliation reduces fruit size and yield and exposes fruit to sunburn. When comparing the severity of an infestation, note the leaf area still on the plant and the fruiting stage. ## Next step The [IPM monitoring record](/mt/ipm-monitoring-sheet/) holds the field counts; organic products are in the [organic crop-protection guide](/mt/organic-pesticide-checks/).