The influence of photoperiod on the thermal requirements for development was discovered for the first time in insects during experiments on the linden-bug, Pyrrhocoris apterus. The effect of photoperiod on the duration of linden-bug development at five constant temperatures (20, 22, 24, 26 and 28°C) was measured and the thermal requirements for development at three photoperiods (14, 17 and 20 h light per day) were calculated. Bugs from four geographic populations were used in these experiments: Pyatigorsk (44°02´N, 43°04´E), Borisovka (50°36´N, 36°01´E), Mikhailov (54°15´N, 39°0´E) and Ryazan (54°36´N, 39°42´E). From the values of individual development times at different temperatures the coefficient of linear regression of development rate (the inverse of the duration) on temperature and the thermal threshold for development were calculated. Both these parameters were found to decrease significantly with decrease in day-length for all four populations studied. It means that at shorter day-lengths nymphal development is less dependent on temperature compared to the development at longer day-lengths. These effects seem to be adaptive. The development times of nymphs at relatively high temperatures (above 24-25°C) are shorter under long-days than under short days which should be advantageous at the height of summer when the days are long and the weather is warm. In the contrast, at relatively low temperatures (below 24-25°C) the nymphs develop significantly faster under short-days than under long days, which is advantageous at the end of summer as it allows the nymphs to reach the adult stage, the only stage capable of overwintering. The influence of photoperiod on the thermal reaction norm appeared to be more or less gradual, i.e. the shorter the day-length the shallower the slope of the regression line of development rate on temperature and the lower the thermal threshold for development. An analysis of the literature shows that this effect of photoperiod on the thermal requirements for development is widespread among insects but has been overlooked by previous authors. The authors conclude that the variation in the development time observed in insects at different seasons, photoperiods or food regimes, or from different populations, etc., are generally due to some modification of the thermal reaction norms and more specifically to differences in the thermal requirements for development.
Myrmica rubra is a northern, temperate Palaearctic ant species with a geographical range that extends from the Atlantic coast of Europe to central Asia. In Europe, its range covers > 25° of latitude where it lives under a variety of climates that vary from extreme oceanic in the west, to continental in the east. Colonies nest in the soil and their life cycles are known to be highly dependent on ambient temperature and soil moisture. We hypothesised that the brood-rearing behaviour of populations might be focally adapted to climate and that we might detect differences when the ants were reared under \"common-garden\" conditions. Brood-rearing behaviour was compared for 38 colonies of M. rubra drawn from 13 populations representing a range of 6 latitudes: all 6 were represented in eastern Europe and 2 in western Europe. A sample of ants from each colony was used to estimate respiration rate, body mass and fat content at the start of the experiment in spring (immediately post hibernation) and at the end of the experiment (mid summer). Respiration had a linear relationship with latitude, with northern populations having greater respiration rate in spring compared to southern populations. It is suggested that this is an adaptation to different seasonality over the species' range that results in the \"more active\" northern workers rearing fewer brood to maturity more quickly than southern workers. Fat content, a measure of worker \"quality\", had a parabolic relationship with latitude with mid latitude colonies having the fattest workers. Fatter workers appeared to rear heavier brood. This probably represented a functional response to environment with populations living at \"edge of range\" sites being physiologically more stressed and performing brood-rearing tasks less well than centre of range populations. We believe that this is the first demonstration of a consistent, intra-specific trend for Variation in the social physiology of an ant species over its geographic range., Graham W. Elmes, Judith C. Wardlaw, Mogens G. Nielsen, Vladilen E. Kipyatko, Elena B. Lopatina, Alexander G. Radchenko, Boyd Barr, and Lit