Behaviour; Activity patterns; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Host parasite relationships; Ecology; Population dynamics; Land and freshwater zones; Palaearctic region; USSR Xiphydria camelus (Xiphydriidae); Hymenopteran parasites; Parasite effectiveness; Distribution upon host; Alnus (alder) & Betula (birch); Ichneumonoidea & Cynipidae parasites & host; Prevalence; Ichneumonidea & Cynipidae; Population density; Parasite density relationships; Russian SFSR; Hymenopteran parasites & distribution alder & birch hosts Aulacus striatus (Aulacidae ); Ichneumonoidea; Activity period; Flight synchronization with Xiphydria (host); Hymenopteran hosts; Xiphydria camelus; Parasite effectiveness; Russian SFSR