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PestNet is a network that helps people worldwide obtain rapid advice and information on crop protection, including the identification and management of plant pests. It started in 1999. Anyone with an interest in plant protection is welcome to join. PestNet is free and is moderated, ensuring that messages are confined to plant protection.
Crops > Vegetables > Crucifers > Chinese cabbage > Possibily Liriomyza, Chinese cabbage, Queensland
September 2012. Small white spots on Pak choy and Bok choy (Chinese cabbages) seedlings sent by DAFF, Queensland. The moment the plants emerge from the ground they get attacked by an insect or so we think causing small white or pale green spots on the cotyledons and new leaves.
Each spot has a small hole associated with it and once the outer epidermal layer is removed the spot is hollow inside. The spots are predominantly on the upper leaf surface. The only insects found are aphids in very low numbers and their associated parasitoid, some fungus gnats and some thrips on yellow sticky traps.
A member replied that this looks very reminiscent of the feeding/egg-laying marks made by the tiny flies of Liriomyzaspp. If it is, eventually you will see small winding leaf mines made by the tunneling larvae. The flies are easy to spot if you watch for a short while- they are 1-2 mm in size, black with some yellow marking. There is plenty of literature on them.