The citrus leaf miner is a major pest of citrus nursery and remains active from March to November. It causes injury to the citrus group of fruits such as lime, lemon, oranges and pomelo.
Caterpillars of this insect feed on leaves by making shiny silvery serpentine mines. The damage distorts the leaves, and the growth of the seedling is arrested as the photosynthesis is adversely affected. The mined leaves turn pale, dry and finally fall down or dry on the branches. The mining injuries serve as foci of infection for the cause of citrus canker, a bacterial disease.
The adult moth is a tiny (3mm) silvery white moth with heavily fringed wings. The female attaches 40-120 transparent eggs singly on the leaves and tender shoots. Within five days they hatch to produce pale yellow and legless larvae which mine into the leaf tissues making a long serpentine convoluted mine. Larval duration is 5 to 10 days.
Mature larvae spin cocoons for pupation in such a way that the margin of the leaf lamina is turned over to protect the pupa underneath. Pupal stage lasts for 5-25 days. Entire life cycle is completed in 12-55 days. There are 9 to 13 overlapping generations in a year.
Some management strategies are :
Collect and destroy the infested leaves. Prune heavily the affected parts during monsoon. Avoid frequent irrigations and split doses of nitrogenous fertilizers.
As the larvae are inside the mines, these cannot be easily killed by insecticidal application. However, application of some systemic insecticides will combat the infestation to certain extent. Spray any one of the following insecticides: Dimethoate 30EC, profenofos 50EC, monocrotophos 36WSC, quinalphos 25EC at 2ml/litre of water, acephate 75SP at 2g/litre of water or imidacloprid 200SL at 375ml/ha.
The spray should be aimed at young leaves only. A second spray should be given after 10 days or apply 5 per cent neem seed kernel extract , 3 per cent neem oil suspension or 2.5 per cent neem cake extract. The larvae and pupae are attacked by natural parasitoids that should be encouraged by avoiding frequent application of toxic insecticides.
(J.Jayaraj, Associate Professor and R.K. Murali Baskaran, Head, Department of Entomology, Agricultural College and Research Institute, TNAU, Madurai - 625 104. phone: 0452- 2422956 Extn: 214)