Common name: berberis sawfly
Latin name: Arge berberidis
Size & characteristics: Berberis and Mahonia have no significant defoliators other than the larvae of the berberis sawfly (Arge berberidis) in the UK. The caterpillar-like larvae are up to 18mm (12 in) long, creamy white with black spots and yellow blotches. The adult sawflies are 7-9mm (14 in) long, bluish black with dark grey wings and upswept antennae. It has several generations during the summer months. Larvae can be found between May and October.
Distribution: Berberis sawfly is a European species that was first confirmed as being present in Britain in 2002, when specimens were sent to the RHS Gardening Advice from Essex and parts of London. It was clear that in some gardens severe leaf loss on Berberis plants had been occurring since at least 2000.
As Berberis has no significant defoliators other than this sawfly, it is reasonable to assume that this pest first entered Britain, possibly with imported plants, at some time during the late 1990s.
Initially, the sawfly made slow progress from the original area of infestation into the counties around London, but by the end of 2010, berberis sawfly had become widespread in England and had reached Wales. It is likely that berberis sawfly will continue to spread and before long reach Scotland.
Thank you to everyone who took part in the survey from 2008 and 2014. More than 900records of the sawfly have been received, greatly adding to our knowledge of this pest.
Hosts and life cycle
Berberis sawfly larvae are found on Berberis and Mahonia species and cultivars, most frequently on Berberis thunbergii.
Adult berberis sawfly can be found flying around Berberis and Mahonia in the spring and summer and have been observed visiting the flowers of Eryngium caerulescens and fennel (Foeniculum vulgare), where they feed on nectar and/or pollen.
The female sawflies insert eggs in batches of up to seven, under the epidermis of the lower leaf surface of host plants.
There are two or three generations during the summer and autumn and so larvae can be found at any time between May and October. When the larvae have completed their feeding, they pupate in the soil within silk cocoons. The final autumn generation overwinters as pupae.
• If damage is to be avoided, host plants should be inspected carefully throughout the spring and summer in order to detect young larvae.
• Removal of larvae by hand can be effective for light infestations.
• More extensive infestations can be dealt with by spraying with insecticides containing pyrethrum, deltamethrin, thiacloprid or lambda-cyhalothrin. Insecticides should not be used during the flowering period as they are harmful to pollinating insects.
RHS advice on Berberis sawfly
Help us with research
The RHS is keen for the data to be used in research projects and collaborations. Email us at Advisory_Entomology@RHS.org.uk if you would like to use RHS data for research. Data is already shared with the National Biodiversity Network.