Symptoms
The common sign is leaf margins curling downwards and inwards until
affected leaflets are rolled into tubes. The rolled leaves contain
an egg or a caterpillar-like sawfly larva that feeds within the
rolled leaflets.
Spot them
The adult sawfly, 3-4mm long, is black in colour with two pairs of
transparent wings. The eggs hatch into pale green caterpillars,
10mm or so long, which feed inside the rolled leaflets. In late
summer June and July the larvae go down into the soil where they
overwinter as non-feeding larvae before pupating in the spring.