The overwintering of the rose-grain aphid Metapolophium dirhodum (Wlk.) on wild roses.
In 1978 and 1979 counts were made during the autumn and spring of the numbers of Metopolophium (c. 90-100% M. dirhodum) found on Rosa spp. in field boundaries, woodland and scrubland on a 7.5 km2 area of farmland in Hampshire. Numbers of M. dirhodum were highest on rose in woodland. Rose in 'dense' woodland had more M. dirhodum than rose in 'open' woodland and numbers were higher on rose in tall unmanaged hedgerows than on rose in short managed ones; very few aphids were found on exposed scrubland rose. The height of surrounding bushes and trees and the degree of shelter they provide were considered important in determining the distribution and abundance of M.dirhodum between the different habitats. Estimates made of the total number of M. dirhodum on Rosa spp, on the farm varied from 232,000 in spring 1979 to 66,000 in autumn 1979. In spring and autumn 1979 populations of M. dirhodum on Gramineae of only one aphid per 32m2 and one per 114m2 respectively would have been required to give an anholocyclic population on the study farm equal in size to that overwintering holocyclically on Rosa spp. However, evidence from several sources indicates that the main mode of overwintering was holocyclic rather than anholocyclic on this study farm in the winter of 1978/1979.