Eugenia Tęgowska

Daily variations in the influence of noradrenaline on preferred ambient temperature of the Siberian hamster.

Daily variations in sensitivity to noradrenaline (NA) and the activation of nonshivering thermogenesis (NST) are important for survival under a potentially wide range of environmental conditions. However, little is known regarding the ability of the Siberian hamster and other species to activate NST in the day and night when they may be subjected to marked variations in environmental temperature. In this study, the effects of acclimation temperature and time of day on the behavioral thermoregulatory response to NA injections in Siberian hamsters (Phodopus sungorus) was investigated. Hamsters were acclimated for 4 weeks to 23 degrees C and a L:D 12:12 h photoperiod. After acclimation, preferred ambient temperatures (PT(a)) in saline- and NA-injected animals were measured continuously in the temperature gradient system. NA (0.6 mg/kg; s.c.) was given every 4 h while PT(a) was monitored. After NA injections there was a rapid drop in PT(a), decreasing to approximately 15 degrees C within 10-20 min after each NA injection. Following 4 weeks of acclimation to 10 degrees C and a L:D 8:16 h photoperiod, the same hamsters were re-tested in the temperature gradient system. Cold acclimation led to an accentuation in the behavioral response with a decrease in PT(a) of approximately 10 degrees C. The maximal decrease in preferred ambient temperatures was recorded during the light phase of the day and during the second part of the night. Lowering of PT(a) after NA allows for rapid dissipation of the heat from NST. Overall, the behavioral response reflects the daily changes in brown adipose tissue sensitivity to NA and thus capacity for NST.

A comparison of the effectiveness of insecticides in constant and variable thermal conditions

ABSTRACT The effectiveness of insecticides differs with changes in temperature, but insecticide toxicities are determined at constant temperatures. Constant thermal conditions do not occur in the field, where insects can change their behaviors to achieve a preferred temperature. The aim of this study was to assess whether the choice of ambient temperature affects the mortality rate of intoxicated firebugs and Colorado potato beetles. The insects’ mortality following insecticide exposure was monitored at constant temperatures (15, 25, and 35 °C) as well as in a thermal gradient system, where the insects could freely select their preferred ambient temperature. Firebugs treated with oxadiazine showed 58% higher mortality when held at a constant temperature post-treatment compared to mortality levels seen when able to choose a preferred temperature in a thermal gradient. Similar results were seen in Colorado potato beetles treated with oxadiazine (15%–33% higher mortality in constant vs. preferred temperature) or organophosphate (36% higher mortality in constant vs. preferred temperature). The insects’ ability to mitigate the impacts of pesticide exposure by selecting more beneficial thermal conditions is an important consideration for pest management. Therefore, the application rates of insecticides used under field conditions should be additionally analyzed to take this factor into account.

Toxicity of Insecticide Carrier Solvent:Effect of Xylene on Hemolymph BiochemicalParameters in Blaberus giganteus L.

Pesticide formulations contain solvents and compounds that improve dispersion and absorption. One of the solvents employed in pesticide concentrates is xylene, an aromatic hydrocarbon widely used in paints, lacquers, or glues. This study was undertaken to evaluate the possible toxic effect of xylene on the giant cave cockroach Blaberus giganteus L. and its role in insecticide formulation toxicity. Different biochemical parameters were determined in cockroaches treated with xylene or pyrethroid formulation, in which xylene is used as a solvent. Xylene induced changes in sugar content and the level of lipid peroxidation similar to changes elicited by treatment with insecticide formulation. The present study shows that xylene induces organismal toxicity in Blaberus giganteus and should not be regarded as a carrier solvent with little biological activity. Since pesticides are always used with adjuvants that can change their toxicity, pesticide formulations should be studied as mixtures for toxic effect.

A comparison of blood buffering capacity in hibernators [Mesocricetus auratus] and non-hibernators [Mus musculus] acclimated to a cold and short photoperiod

Differences in blood buffering capacity and in blood glucose level homeostasis were examined in hibernators (golden hamsters) and non-hibernators (house mice) acclimated to a cold environment and short photoperiod. First, the pH and glucose levels were investigated in experimental animals maintained at a temperature of 22C and a 12:12 light-dark cycle (control group) and then after a two-week period of adaptation to low ambient temperature and short photoperiod (temperature of 10C and a 8:16 light-dark cycle) and additionally after 10 l of 10% lactic acid was added to 450 l of freshly collected blood samples. The pH of blood in cold acclimated animals decreased in comparison with control ones. In non-hibernators blood pH was significantly lower than in hibernators. The addition of lactic acid to blood samples results in a sharper drop of blood pH in non-hibernators than in hibernators. In control animals glucose levels didn’t differ significantly between non-hibernators and hibernators, whereas after the cold acclimation period glucose levels in non-hibernators and hibernators stabilized at virtually the same but lower level. The results of blood glucose level measurements clearly indicated that this level – 130 mg/dl is the regulated level of glucose in the blood of both groups of animals. An improved buffering capacity of the blood revealed in hibernators could be considered as an adaptation to alleviate potentially negative effects of both respiratory acidosis and metabolic acidosis which accompany entrance into hibernation and arousal from hibernation. In conclusion the differences in buffering ability of blood to the resistance of changes of pH due to the addition of acid, revealed for non-hibernators and hibernators, indicate better adaptation of hibernators subjected to cold to their life in this environment.