How to recognise it
The larvae are green/white, caterpillar-like creatures which grow up to 1cm long. The adults are up to 3-4mm long with two pairs of wings, resembling flying ants.
Females lay eggs on leaves which they have probed (ie which are rolled) in May/June, which hatch a week later. The larvae feed on the rolled leaf for about 4 weeks then move into the soil to overwinter in cocoons, before pupating in early spring and emerging as adults in May/June.
Why it’s a problem
The female adults probe the leaves with their ‘ovipositors’ (a piercing device used to lay eggs) in May/June, laying eggs in some of the leaves they have probed. This probing secretes a chemical which causes the leaves to roll downwards, along both long edges, which is a permanent effect. No other damage is done to the plant (the leaves do not fall early), but the curled leaves can look unsightly.
Where you are likely to find it
On roses in May, particularly on the following cultivars: ‘Peace’, ‘Albetine’, ‘Frensham’, ‘Golden Wings’, ‘Grand’mère Jenny’, ‘Masquerade’, ‘Mischief’, ‘Mme Butterfly’, ‘New Dawn’, ‘Queen Elizabeth’ and ‘Sutter’s Gold’.
Warm weather in May and June is likely to increase the egg-laying activity and the subsequent population.
How to deter it
Roses with thick, shiny leaves and roses grown as standards are less susceptible to infestations of this sawfly.
Regular winter/early spring digging will expose any overwintering larvae and kill them (by exposure to the weather and predators).
How to get rid of it
Pick off affected leaves in May/June and burn them; this will remove the eggs/larvae laid by the adults. However, this is not a practical solution if a large number of leaves are affected as this will be detrimental to the growth of the plant.
If you wish to use a chemical control then contact or systemic insecticides may help to reduce the population, although they are not always effective. Spray in May/June to reduce the egg-laying of the female adults and again later in the season to reduce larvae numbers.
Is it good for anything?!