Research
Berberis sawfly adult. Image: CSL
Berberis sawfly
Introduction
Berberis sawfly (Arge berberidis) is a European species that was first confirmed as being present in Britain when an adult female was sent to the Royal Horticultural Society's Members' Advisory Service in April 2002. It came from a private garden at Church Langley, Essex, where Berberis thunbergii plants had been defoliated the previous year.
The RHS learnt of other sightings of this pest in the London area during 2002, and 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 the sawfly, it is reasonable to assume that this pest first entered Britain, possibly with imported nursery stock, at some time during the late 1990s.
Distribution
Records of the sawfly's distribution have been kept in subsequent years through enquiries sent to the RHS Advisory Service and other sources.
The distribution map below shows the distribution up to the end of 2007. Initially, the sawfly made slow but steady progress from the original area of infestation in the counties around London, but by 2004 there were more distant records near Lacock, Wiltshire, and Dover, Kent. These may have resulted from the movement of infested plants, rather than flight dispersal by adult sawflies. By the end of 2007, berberis sawfly had consolidated its presence in south east England and has now been found in Hampshire, Wiltshire, Somerset, Warwickshire, Nottinghamshire, Northamptonshire, Gloucestershire, Cheshire and Yorkshire.
It is likely that berberis sawfly will continue to spread and before long may be found in Wales and Scotland. The Entomology section at Wisley is interested in receiving sightings of the adults, larvae or defoliated berberis plants, particularly from areas outside south east England.
Click here to submit a record of Berberis sawfly
Map of berberis sawfly distribution
Distribution of Berberis sawfly in England. From Records held by the RHS (at December 2007). Produced using DMAP©
Berberis sawfly larva. Image: RHS Biology
Berberis sawfly is likely to be mainly a garden insect in the UK, as that is where its food plants are most likely to be found. There are two or three generations during the summer and autumn and so larvae can be found at almost any time between May and the end of October. When the larvae have completed their feeding, they go down into the soil where they pupate inside silk cocoons.
The sawfly's larvae are up to 18mm (3/4in) long, with black heads and creamy white bodies marked with black dots and yellow blotches. They are found most frequently in gardens and amenity plantings on Berberis thunbergii and its many cultivars. The larvae also feed on Berberis vulgaris , but that is a relatively scarce wild plant in Britain. Other cultivated Berberis species and hybrids on which larvae have been found are Berberis 'Georgei', B. jamesiana and B. x ottawensis . The larvae also feed on the foliage of some Mahonia species and hybrids.
Adult Arge berberidis are 7-9mm (about 1/4in) long and are bluish black with dark grey wings and upswept antennae. They have been found visiting the flowers of Eryngium caerulescens and fennel (Foeniculum vulgare), where they feed on nectar and/or pollen. The females deposit their eggs in batches of up to seven eggs, which are inserted under the epidermis of the lower leaf surface of its host plants.
Control
The larvae of Berberis sawfly feed in relatively exposed positions on the foliage and are susceptible to most insecticides. If damage is to be avoided, host plants should be inspected carefully throughout the spring and summer in order to detect the 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, thiacloprid or bifenthrin. Insecticides must not be used during the flowering period as they are harmful to pollinating insects.
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