Photoperiod modifies thermal reaction norms for growth and development in the red poplar leaf beetle Chrysomela populi (Coleoptera: Chrysomelidae).

Regression lines of development rate on temperature appeared significantly different between long (22 h) and short (12 h) day conditions and intersected each other at 23.8°Ð¡. Thus, the rate of growth and development was higher at temperatures below the intersection point under short-day but above the intersection point it was higher under long day. Ecological relevance of this effect seems as follows: in autumn, as nights become longer and average daily temperature decreases, larvae have to speed up their development because it is only imago that overwinters. Conversely, midsummer offers long days and usually higher temperature, so again it is advantageous to develop as fast as possible in order to have at least one more generation per year. These results are compared with other studies showing interactions between photoperiod and temperature, and some possible general patterns are outlined. The lower thermal threshold for larval development depended on photoperiodic conditions; therefore rate isomorphy must be violated in this species. Development at higher temperatures generally resulted in smaller adults, as is usual with ectotherms according to the "temperature-size rule", but body weight depended significantly on temperature only under short day. Our estimates of the lower temperature thresholds for growth and development in both cases did conform to the generalization made previously by Walters and Hassall (2006) in spite of another formula used by us. We briefly discuss this phenomenon and argue that relative position of these thresholds can be explained mathematically and per se may lack any biological sense.

Critical thermal minima, their spatial and temporal variation and response to hardening in Myrmica ants.

In a changing environment the ability to adjust physiological functions to new conditions might be especially valuable for long-living ectothermic animals such as ants. With a simple method for estimating critical thermal minima of Myrmica ants we assessed variation of the minima and their response to lowered temperature. At a cooling rate of about 1 degree C per minute the ants first displayed knock-down (at temperatures 1.5 to -0.2 degree C) and only later immobilized completely (at -1.3 to -3.1 degree C). Pre-chilling of ants at 5 degree capital ES, Cyrillic for 1 h lowered the parameters significantly but not greatly (about 0.9 degree capital ES, Cyrillic). Constant laboratory conditions (20 degree capital ES, Cyrillic) raised the knock-down temperature and tended to lower the temperature of immobilization. In the same manner the two parameters changed in field conditions in June, but no significant change occurred through August and until the end of study season in mid-September. When populations from different geographic localities were compared, populations from the north showed lower knock-down temperatures. The magnitude of these apparently genetic differences among populations was comparable to the magnitude of plastic changes that occurred either naturally, or in experiments, or in laboratory culture. The little plasticity and low geographic variation of the critical thermal minima may indicate that the ability of the ants to withstand cold events and populate varying climates bases mainly on the protective properties of nesting substrate.