Berberis sawfly

Berberis sawfly became established in south-east England in about 2000, although it was not detected until 2002. It has since spread throughout most of England. It is the only  pest of Berberis, likely to cause severe defoliation.

Berberis sawfly larvae.

Quick facts

Common name Berberis sawfly
Latin name Arge berberidis
Plants affected Some deciduous Berberis, especially B. thunbergii, and Mahonia
Main symptoms Leaves are eaten by caterpillar-like larvae. Plants may be completely defoliated
Caused by Caterpillar-like larvae of a sawfly
Timing May-October

What is berberis sawfly?

Creamy white, spotted caterpillar like larvae with black heads feed on the foliage of berberis and Mahonia often causing severe defoliation.

Symptoms

Plants attacked by berberis sawfly are easy to spot:

  • Branches or the whole plant can be defoliated
  • On closer inspection, black-headed, creamy white caterpillar-like larvae with black spots and orange yellow blotches can be seen feeding on the foliage
  • The adults are shiny black insects, up to 8mm long, with greyish-black wings.

Control

Non-chemical control

Check plants regularly between late April and October for the presence of larvae. Hand removal may not be possible due to the spines on the stems of a berberis.

If a plant is repeatedly attacked consider replacement it with a non-susceptible alternative.

Chemical control

The larvae can be controlled by spraying the shrub with pyrethrum (e.g. Py Spray Garden Insect Killer, Bug Clear Gun for Fruit and Veg, Defenders Bug Killer or Growing Success Fruit & Veg Bug Killer), deltamethrin (e.g. Bayer Sprayday Greenfly Killer) or lambda-cyhalothrin (Westland Resolva Bug Killer).

Do not spray plants while they are in flower due to the danger to pollinating insects.

Download

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

Biology

There are two generations during the summer and there may be a third generation in autumn.

The adult sawflies are 7-9mm long and are shiny black with darkened wings. The antennae are characteristically swept upwards.

Eggs are inserted under the epidermis on the underside of leaves in batches of up to seven eggs. These hatch into caterpillar-like larvae that proceed to devour the foliage.

When fully grown the larvae are up to 18mm long. They go into the soil to pupate within silk cocoons. This pest overwinters in the ground as pupae.

    Berberis sawfly adult

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