Large rose sawfly

The caterpillar like larvae of large rose sawflies eat the leaves of wild and cultivated roses.

Larvae of large rose sawfly. Image: RHS, Horticultural Science

Quick facts

Common name Large rose sawfly
Scientific name Arge pagana and Arge ochropus
Plants affected Wild and cultivated roses
Main symptoms Split shoots and defoliation
Most active Late May to October

What is large rose sawfly?

Large rose sawflies are insects with pale spotted black, green and yellow caterpillar-like larvae that eat the leaves of roses, sometimes causing severe defoliation. The adults have yellow abdomens with mainly black thorax and heads.

Roses can also be attacked by other sawflies such as the rose leaf-rolling sawfly.

Symptoms

You may see the following symptoms:

  • The female sawflies lay eggs in soft young rose stems. The stems often split open where the eggs were laid, resulting in elongate scars
  • Whitish green, caterpillar-like larvae with black spots and yellow blotches cause extensive defoliation in early and late summer

    Elongated scars on stems are caused by the female sawflies laying eggs in the shoots and flower stalks. The larvae cause extensive defoliation in early and late summer, as they feed on the leaves and shoots.

    Control

    Non chemical

    The larvae can be removed by hand. If eggs are present in the stem these can also be destroyed.

    Chemical control

    Organic pesticides, such as pyrethrum (e.g. Py Spray Garden Insect Killer, Bug Clear Gun for Fruit and Veg, Defenders Bug Killer, Growing Success Shrub and Flower Bug Killer) will control young larvae but older ones are more tolerant of these insecticides.

    Heavy infestations can be sprayed with deltamethrin (e.g. Bayer Sprayday Greenfly Killer), lambda cyhalothrin (e.g. Westland Resolva Bug Killer), or the systemic insecticide thiacloprid (e.g. Provado Ultimate Bug Killer).

    Plants in flower should not be sprayed due to the danger to pollinating insects.

    Download

    Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

    Biology

    In Britain there are two species of large rose sawfly: Arge pagana and A. ochropus. The adult insects of both species have yellow abdomens with the legs, thorax and heads being mostly black. Arge pagana is the more common species. 

    Rows of eggs are inserted into soft young rose shoots and female sawflies are sometimes seen dangling from such stems, attached only by their saw-like egg-laying organs.

    After hatching, the larvae feed together in family groups. They are pale green with black spots and yellow blotches, and are up to 25mm (about 1in) long. When fully fed, they go into the soil to pupate.

    The large rose sawfly (Arge pagana) will produce two (sometimes three) generations from May to October. Arge ochropus usually has a single generation in early summer, but sometimes there is a second generation in late summer.

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