Insects experience important selection pressures from their parasitoids, which affect both their population dynamics and their evolutionary responses. The interaction between the egg parasitoid Oomyzus galerucivorus Graham (Hymenoptera: Eulophidae) and its chrysomelid host Galeruca tanaceti L. (Coleoptera: Galerucinae) was investigated with the particular aim determining whether the chrysomelid host can escape its parasitoid by ovipositing late in the year as early as September. Although the leaf beetle and its parasitoid emerge in April, G. tanaceti starts to oviposit after spending the summer in reproductive diapause. The objective was to determine, whether the small parasitic wasp can parasitise its host's eggs even at the end of its host's reproductive season in December, when temperatures are low. Beetle oviposition, parasitism rates and temperatures were measured on three comparable mesoxerophytic grassland sites over the coarse of a season. Beetle oviposition, but not parasitism, was significantly positively dependent on temperature. Rate of oviposition decreased over the oviposition period with decrease in temperature. In contrast, after a lag phase of 1-2 weeks at the beginning of the oviposition period in September beetle egg clutches were parasitised at a constant rate until the end of the season in December. Host eggs were parasitised even at mean daily temperatures of 0-6°C. Thus the tansy leaf beetle does not escape from egg parasitism by ovipositing late in the season in central Germany.
The seasonal activities of the European pigeon tick, Argas reflexus, in Berlin were investigated (a) by trapping locomotory active ticks and (b) by determining the occurrence of tick-invasions into human habitations. Tick trapping was carried out in two tick-infested attics in 1988. Pigeons were available for ticks in one of the attics only, while a previously existing bird colony was expelled from the other. Ticks were trapped by means of smooth V- shaped metal gutters cemented to the attic walls. Trapped nymphal and adult ticks were marked and released into cracks of the attic wall inside the rectangular traps in two-weck-intervals. During the one-year-study a total of 2081 ticks was trapped, 83% of which were larvae, 10% nymphs, 4% females and 3% males. Only 4.4% of the 366 ticks marked were recaptured. There is strong evidence that locomotor activities of A. reflexus were restricted to host-seeking and returning to a resting-site after a blood meal. Activities of all postembryonic stages peaked from March through early June, irrespective of whether or not hosts were available to the ticks. The immature stages displayed another peak of activity in late summer/autumn. A total of 51 cases of A. reflexus-infested buildings was reported from the public to public-health offices in Berlin from April 1989 to March 1993, 45 of which represented tick invasions into human habitations. About 60% of them occurred in spring, thus largely confirming the results of seasonal trapping.