Why is it a threat? Although not yet detected in Bhutan, the tomato leaf miner is a devastating pest of tomato. Tomato plants are attacked in all the growth stages in both open fields and greenhouses. Although using pesticides is now thought to be an effective management method, there have been numerous reports of tomato leaf miner acquiring insecticide resistance. This pest also attacks potato, brinjal, pepper, common beans, broad beans, cow pea, tobacco, and wild radish.
Adult moths are small (5-7 mm long and with a wingspan of 8–10 mm). grey-brown with filiform (bead-like) antennae and black spots on the forewing. Eggs are small (0.35 mm long), cylindrical, and creamy white to yellow. Larvae (L1) are whitish to yellowish and mine inside the tomato leaves. In the second to fourth instars, they turn greenish to light pink. Pupae are greenish initially, becoming dark brown with time.
Larvae can feed on apical buds, leaves, stems, flowers, and fruits. Larvae mine the leaves, producing blotch-shaped mines. They prefer leaves and stems, but fruits are also attacked.
Confusion with other pests: The only insect pest currently reported to cause leaf-mining and boring damage to tomatoes and potatoes is the potato tuber moth (PTM).
The tomato leaf miner can lay up to 260 eggs each and can complete up to 10-12 generations a year under favorable conditions. The lifecycle is completed within 30–35 days. Adults are nocturnal and hide between leaves during the day. There are four larval instars (stages). Pupation may take place in the soil, on the leaf surface, or within mines. The tomato leaf miner can overwinter as eggs, pupae, or adults, depending on environmental conditions. Larvae do not enter diapause when food is available.
Dispersal: Movement of infected tomatoes, tomato plants, and used containers is known to be a high-risk pathway. Outdoor markets that sell infested fruit would pose a great risk. Adults have been reported to fly up to 100 kilometers, so populations could easily spread once established in Bhutan.
When can damage be expected? The tomato leaf miner can cause serious damage throughout the tomato growing season.
Hosts: It is primarily a tomato pest, but it also attacks potato, brinjal, pepper, common beans, broad beans, cow pea, tobacco, and wild radish.
The tomato leaf miner is one of the most challenging pests to control.
- Pheromone traps can detect the presence of the tomato leaf miner.
- Monitor tomato from seedling stage till the full harvesting stage. In the morning, look for adults, eggs, larvae, and mines on leaves.
Effect of variety
unknown in Bhutan.
- Remove and destroy any infested plants or tomato plant parts (fruits, leaves, stems).
- Destroy (burning and burying) crop residue after tomato harvesting.
- Remove wild solanaceous plants and weeds in the vicinity of the field that might host this pest.
- Greenhouses should be fitted with insect nets to prevent entry of this pest.
At this point, the primary method of management is the use of insecticides. However, this is difficult as larvae feed inside leaves, fruits, and stems.
Note: This pest has not yet been recorded in Bhutan. Please contact the NPPC immediately if its presence is suspected.
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Image acknowledgements: http://www.tutaabsoluta.com/tuta-absoluta; An overview on Tuta absoluta, identification, origin, distribution, damage and economic impact. Prepared by Mr. Lalit P. Sah/ Agay P. Giri.