none Population budgets for Rhynchaenus fagi , based for the most part on samples of beech leaves taken in June, were constructed for a 10-year period (Northern Ireland) and a 3-year period (Scottish borders). There were years of sustained population growth and sustained decline, but not enough evidence to suggest a cycle. Similar population levels were found at both sites in all but one year. Key factors were associated with the adult stage, although egg mortality may also make a significant contribution to population change. Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Ecology; Population dynamics; Abiotic factors; Physical factors; Land and freshwater zones; Palaearctic region; Europe; United Kingdom Rhynchaenus fagi (Curculionidae); Hymenopteran parasites; Colastes braconius & Eulophidae; Residual mortality relationship; Plant hosts; Fagus sylvatica (beech); Mortality, parasitism & population changes relationships; United Kingdom; Population changes; Population regulation; Density dependent factors evaluation; Temperature; Mortality relationship; Northern Ireland & Scotland; Northern Ireland; County Tyrone; Pomeroy; Scotland; Tweedale district; Peebles, influencing factors Colastes braconius (Braconidae ); Eulophidae; Coleopteran hosts; Rhynchaenus fagi; Host residual mortality relationship; Northern Ireland; County Tyrone; Pomeroy; Coleopteran host residual mortality relationship