An analysis of diapause and resistance in the egg stage of Floronia bucculenta (Araneida: Linyphiidae) : A contribution to winter ecology.

Floronia bucculenta hibernates in the egg stage; the egg sacs are deposited on the leaves of grass tussocks without any shelter. The morphogenesis of the eggs was divided into 10 arbitrarily chosen stages, in order to test the dependence of embryonic development on temperature in the laboratory. The eggs developed slowly at 23°C, 16°, 12.5°; embryogenesis stopped after 70-45 days, when prosomal appendage rudiments began to form. At 10°, 7.5°, 5°, 0° complete embryogenesis was possible until the emergence of the first complete stage. The eggs developed most rapidly at 5° (mean developmental time 203 days). The egg development was "normal" at 5° and 0°, when compared with the timetable of the embryogenesis of the linyphiid Bathyphantes gracilis, a species which has no egg diapause. At 7.5° and 10° the embryogenesis was strongly delayed during the median phases of development (elongation of the germ band, formation of prosomal appendages); after reversion the development was accelerated (postdiapause phase). After long exposure to low temperatures (-10° to +10°) the diapause was terminated. A temperature of 0° was optimal (minimal time of exposure 8-9 weeks). The time required for embryonic development of postdiapause eggs decreased hyperbolically with increasing temperature. In the field the median phases of embryogenesis were retarded by low ambient temperatures; diapause was terminated from late December to mid-January. The spread of hatching in spring was 7-15 days.During the diapause phase the O2-consumption of the eggs at 25° was depressed. It rose from 1.55 (in late diapause) to 4.21 ml/100 eggs·h at the onset of postdiapause, whereas O2-utilization did not change significantly at 5° (from 0.54 to 0.61 ml/100 eggs·h just after the termination of diapause).The diapause phase was not characterized by higher resistance to cold, drought, or flooding. As compared with single eggs removed from the cocoon, the silken wall of the intact egg sac did not affect the survival of postdiapause eggs exposed to-15° (LD50=28 days); it raised, however, the survival time of eggs exposed to a R.H. of 32% (at 5°) or flooding by distilled water (at 5°): from LD50=37 to 68 days at drought, from LD50=30 to 92 days at flooding.Diapause is important for synchronizing the life-cycle of F. bucculenta with the seasonal fluctuations of environment. The egg stage is highly tolerant to the extreme factors of the winter. Some implications of the relation of the studied spider to its habitat are discussed.