Pest name: Athalia rosae
Common name: Turnip sawfly
Turnip sawfly larvae
Identification:
Adults: Approximately 6-8mm in length, adults resemble ants but without the 'waist' between the thorax and the abdomen. The male is smaller than the female.
The hind part of the body is yellowish to yellowish-orange, the head and sides of the thorax are shiny black and the transparent wings
have a darker front edge.
Larvae: Larvae are 16-18mm in length with wrinkled skin dotted with several small pupillae. The head capsule is shiny black. Recently hatched larvae are
pale grey to greenish in colour, whilst older larvae change colour to become dark green to black on the back and grey on the ventral surface.
In addition to the three pairs of thoracic legs, the larvae has 7 pairs of ventral abdominal prolegs and an anal pair.
Eggs: Eggs are laid in a small cell chamber made by the female on the edge of the leaf.
Biology:
Adults: Adults emerge from the ground in May/June and mate on the same day they emerge. Egg laying begins a few days later. After feeding, the female makes
cuts into the leaf surface with her ovipositor and deposits eggs individually into these small chambers.
Eggs: Embryonic development lasts 6-8 days. Unfertilised eggs always produce male offspring, fertilised eggs produce female offspring.
Larvae: at 20°C, the larvae can consume twice their own weight in 24 hours. Larval development takes about 20 days in the UK, during which they will
have three moults. Once the larvae are fully grown they move down into the soil where each forms a silky cocoon within which to pupate.
Life cycle:
Adults occur from May to October, with up to 3 generations per year. They require warm conditions to survive and fly only at
temperatures above approximately 18°C. A single female can lay up to 300 or more eggs in the leaf margins of host plants.
The young larvae mine within the leaf tissue, whereas older larvae can cause skeletization by eating the leaves from the underside and edge,
leaving only the veins.
Summer pupation lasts about 3 weeks, but larvae of the final brood enter the soil to overwinter.
They pupate in the spring and adults appear shortly afterwards.
