Scientific name: Blennocampa phyllocolpa
Plants affected: Wild and cultivated roses
Main symptoms: Tightly rolled leaves
Most active: Late April to July
What is rose leaf rolling sawfly?
Sawflies are in the same group of insects as bees, ants and wasps (the Hymenoptera). They have caterpillar like larvae that feed on plants the adults are winged insects that can appear fly-like.
Rose leaf-rolling sawfly is an insect that can cause tight rolling of rose leaves in spring and early summer. Female sawflies insert eggs into rose leaflets, and while doing so, secrete chemicals that induce leaf rolling. Sometimes the leaflet is probed but no egg is laid, this process still results in leaf curling. Caterpillar-like larvae hatch from the eggs and feed within the rolled leaflets.
Roses usually recover from any damage caused by this insect.
You may see the following symptoms:
- Leaf margins curl downwards and inwards along their length until affected leaves are rolled into tubes. This occurs during late April to early June, and takes place within 24 hours of an egg being inserted into the leaf base
- Pale green larvae feed inside the rolled leaves. The remains of rolled leaves can stay on the plant throughout summer
- This species is can be reported as part of teh Big Garden Sawfly Survey (external link)
This sawfly can usually be tolerated as part of the biodiversity roses support, there may be a loss of vigour where a large proportion of foliage is affected although plants usually recover.
Affected leaves can be picked off before the larvae complete their feeding; this is only feasible when comparatively few leaves are affected. The removal of large numbers of leaves will be more harmful to the rose than damage caused by the sawfly. Cultivation of the soil around roses during the winter may expose overwintering larvae, but may damage the roots and encourage suckering.
Pesticides are unlikely to control this insect. It is also impractical and due to potential harm to non-target invertebrates (including sawfly predators), undesirable to attempt to prevent the females laying eggs, they can be active over an eight week period in late spring to early summer. Larvae within the rolled leaves are largely protected from pesticides.
The adult sawfly is 3-4mm (about 1/8in) long, black in colour with two pairs of transparent wings. The females insert eggs into the leaflets during late April to early June and while doing so secrete chemicals that induce leaf rolling.
The eggs hatch into pale green caterpillar like larvae, which grow up to 10mm (about 3/8in) long as they feed inside the rolled leaflets. During late June and July the larvae go down into the soil where they overwinter as non-feeding larvae before pupating in the spring. There is one generation per year.
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