Research
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. Other records of this pest in the London area came to the attention of the RHS 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 in 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. Two distribution maps (see below), prepared with DMAP© software, show the distribution up to the end of 2004 and 2006. Initially, the sawfly made slow but steady progress from the original area of infestation in the counties around London, but by 2004 there were a couple of 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 2006, berberis sawfly had consolidated its presence in southeast England and has now been found in the Southampton, Bristol, Coventry, Manchester and York districts. 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 to receive sightings of the adults, larvae or defoliated berberis plants, particularly from areas outside southeast England.
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Distribution map to 2004
Distribution map to 2006
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. The sawfly's larvae are up to 18mm 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', Berberis jamesiana and Berberis x ottawensis. The larvae also feed on the foliage of some Mahonia species and hybrids. Adult Arge berberidis are 7-9mm 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.
For further information on the biology and identification of Arge berberidis, see Halstead, A J. (2004). British Journal of Entomology and Natural History 17 p131 - 135.