Berberis sawfly

Berberis sawfly became established in south-east England in about 2000. It has since spread throughout most of England and into parts of Wales. It is the only insect that feeds on Berberis and Mahonia, likely to cause severe defoliation.

Berberis sawfly larvae.

Quick facts

Common name Berberis sawfly
Latin name Arge berberidis
Plants affected 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?

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.

Berberis sawfly has creamy white, spotted larvae with black heads. They feed on the foliage of Berberis and Mahonia and can cause severe defoliation. This species of sawfly will only feed on these two plants. The adult insect is shiny black, up to 8mm long, with greyish-black wings

 

Survey

Seen berberis sawfly? We would like to know.

As part of our research the RHS would like to know where berberis sawfly has been seen.

Please submit your records via our berberis sawfly survey (expected time to complete survey = two minutes).

Submissions to our pest and disease surveys are stored permanently in an anonymised form in order to monitor the spread of the pest or disease. We may contact you within 2 months of your submission in order to verify your sighting but your personal data will not be permanently stored in connection with your submission and will be deleted after 1 year. We publish and share only non-identifiable data from survey submissions (such as a six figure grid reference) with third parties and the public for the purposes of scientific research and advancing understanding among gardeners.

Thank you to everyone who has submitted records so far – read a blog about the surveys 

Watch an animated map of the results from the berberis sawfly survey (links to YouTube) 

Symptoms

Plants with by berberis sawfly are easy to spot:

  • Branches or the whole plant can be defoliated, berberis sawfly is the only insect likely to cause such severe defoliation
  • On closer inspection, black-headed, creamy white caterpillar-like larvae with black spots and orange yellow blotches may be seen feeding on the foliage
  • The adults are shiny black insects, up to 8mm long, with greyish-black wings. They appear similar to many other species of sawfly
  • Sawfly larvae on plants other than Berberis or Mahonia will be a different species. 

Control

Check Berberis and Mahonia frequently from spring onwards so action can be taken before a damaging infestation has developed. When choosing control options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section. If this is not sufficient to reduce the damage to acceptable levels then you may choose to use pesticides. Within this group the shorter persistence pesticides (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action.

Non-pesticide control

  • Where possible tolerate populations of sawfly
  • Encourage predators and other natural enemies of sawfly in the garden, such as birds and ground beetles.
  • Check plants regularly from the end of May for the presence of larvae and remove by hand where practical
Pesticide control
  • If numbers of larvae are too high for hand picking, control may be achieved by spraying with pesticides. Spraying at dusk is likely to give the best results
  • Organic contact insecticides containing natural pyrethrins (e.g. Bug Clear Gun for Fruit & Veg, Neudorff Bug Free Bug and Larvae Killer). Several applications of these short persistence products may be necessary to give good control
  • More persistent contact insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer)
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
Follow label instructions when using pesticides. 
Plants in flower should not be sprayed due to the danger to bees and other pollinating insects.
Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener.

Download

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

Biology

There are two generations of berberis sawfly 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 swept upwards.

Eggs are inserted under the epidermis on the underside of leaves in batches of up to seven. 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 insect overwinters in the ground as pupae.


Gardeners' calendar

Find out what to do this month with our gardeners' calendar

Advice from the RHS

Did you find the advice you needed?

RHS members can get exclusive individual advice from the RHS Gardening Advice team.

Join the RHS now

Get involved

The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.