Gypsy moth, Lymantria dispar, outbreak in northeast London, 1995 – 2003

Abstract

A small outbreak of the gypsy moth, Lymantria dispar (L.), was discovered in June 1995 in the South Woodford area of northeast London, near Epping Forest. The origin of this outbreak remains unknown, but the eggs may have been transported from continental Europe, where major outbreaks occurred in the early 1990s. A risk assessment concluded that severe defoliation by this forest pest was unlikely to occur in the UK under current climatic conditions, but if the gypsy moth did become established, then sporadic damage to amenity tree species could be expected. Therefore an eradication programme was undertaken, which involved determining the extent of the outbreak area via population monitoring, and chemical treatments of any larval infestations, to prevent further spread. A series of targeted publicity campaigns was carried out with the aim of raising public awareness of the pest in the wider outbreak area. Details of gypsy moth finds (egg masses and larvae) and pheromone trap catches (adult males) are given for the years 1995 – 2003. Pheromone traps were maintained at a relatively high density (c. 188 per 1 km2) in the immediate outbreak area—and similarly in an adjacent portion of the Epping Forest—and it remains a possibility that some mating disruption has occurred. Although Lymantria dispar persists at this site, the numbers of adult male moths trapped has declined markedly in comparison to the first 2 years (1995 – 1996). The outbreak is, however, continuing to persist at a very low level and may be becoming more widely dispersed, albeit very sparsely. It is also possible that observed population trends in terms of pheromone trap catches reflect a natural population cycle, and for these reasons work is continuing in an attempt to eradicate this damaging broadleaf tree pest from the UK.