Chrysomela populi Linnaeus, 1758

This transpalaearctic species is locally common in most European countries from Portugal to Turkey and Iran, north to the UK and northern Fennoscandia and across North Africa, in the east it extends to Japan and Korea and south to India and Pakistan. In the UK it is very local and generally scarce across England and Wales north to the Lake District; in Wales it is mostly coastal while in England there are three main areas of occurrence, the southeast including Hampshire and the Dorset coast, the West Country and the northeast around the Humber, elsewhere there are a few scattered records and it is thought to have declined in recent decades, especially in the north. Our UK experience hardly reflects the continental occurrence of the species where it may be very common in warmer countries and even in northern areas may be abundant e.g. in Poland it is one of the most serious pests of commercially grown poplars and is variously controlled with insecticides, and there are regular accumulations of damaging populations in central Sweden. Adults occur year-round, they overwinter under bark or among leaf-litter around host trees and are very rarely active before April, they peak in abundance from May to August and persist into September or, rarely, October. Host plants include various species of Salix L. and sapling specimens of Populus L., especially P. tremula L. but also P. x canescens (Aiton), P. nigra L., P. Canadensis Moench and P. maximowiczii A. Henry, and among the willows recorded as hosts are S. repens L., S. caprea L., S. cinerea L. and S. alba L. Mating occurs in the spring after a period of feeding when the adults eat large round holes into developing host foliage, oviposition begins soon after and continues into early summer; eggs are laid in batches of about 20 on the underside of leaves and larvae emerge after about 10 days. Larvae feed communally on the underside of leaves, often stripping them completely; they develop quickly, passing through 3 instars and becoming fully-grown within a month. Pupation occurs on stems or the underside of leaves and this stage lasts about 2 weeks. New generation adults occur from late June into September and so the summer peak of abundance will include both generations, early adults feed through the summer but do not mate until they have overwintered. Adults are fully-winged but rarely fly.