Tolerance of two honey bee races to various temperature and relative humidity gradients Hossam F. Abou-Shaara*, Ahmad A. Al-Ghamdi, Abdelsalam A. Mohamed Baqshan`s Chair for Bee Research, Plant Protection Department, College of Food and Agricultural Sciences, King Saud University, P.O. Box. 2460, Riyadh 11451, Saudi Arabia *Corresponding author, E-mail: entomology_20802000@yahoo.com Abstract here are various factors that can have an efect on honey bee colonies. Temperature and relative humidity, in particularly, have special importance for honey bee colonies. Relatively few studies have been conducted on the efects of temperature and relative humidity on honey bee races. Here, the efects of diferent levels of temperature and relative humidity on survival, tolerance and body water loss were investigated on two races, one adapted to harsh conditions (Yemeni honey bees) and the other adapted to normal conditions (Carniolan honey bees). Results showed that temperature had higher efect than relative humidity on workers survival and Yemeni honey bees were more tolerant to elevated temperature than Carniolan honey bees. Moreover, rates of body water loss for the two races were high under elevated temperature and low humidity conditions. In general, the response of the two races in the studied treatments was somewhat similar. However, under extreme conditions at elevated temperature or low humidity, Yemeni honey bees showed higher tolerance than Carniolan honey bees. Key words: Apis mellifera carnica, Apis mellifera jemenitica, honey bees, humidity, temperature, tolerance, survival. Abbreviations: RH, relative humidity. Environmental and Experimental Biology (2012) 10: 133–138 Original Paper Introduction he importance of temperature and relative humidity for honey bees is well known, and all activities of honey bee colonies are under the control of these factors. Temperature, in particularly, is very important for internal as well as external activities of honey bee colonies. Maintaining a suitable range of temperature from 33 to 36 °C inside colonies is very important for honey bees (Petz et al. 2004). Deviation from this range can afect the developmental period of honey bee immature stages, emergence rate (Tautz et al. 2003), colour of emerged bees (DeGrandi-Hofman et al. 1993), wing morphology (Ken et al. 2005), learning ability (Tautz et al. 2003), adult brain (Groh et al. 2004) and disease prevalence. Also, ambient temperature has a great efect on foraging activity, as high temperature has a negative efect on bee foraging (Cooper, Schafer 1985; Al- Qarni 2006; Blazyte-Cereskiene et al. 2010). Moreover, very low temperature below 10 °C can prevent light activity (Joshi, Joshi 2010). On the other side, relative humidity has a particular importance within the colony where high humidity is mostly required for brood development (Human et al. 2006). Efect of humidity on egg hatching rate has been previously identiied (Doull 1976) and a relative humidity about 75% within colonies could be considered as suitable for immature stages (Ellis et al. 2008). In the case of external activities, no clear direct impact of relative humidity on honey bees has been reported, including foraging activity (Joshi, Joshi 2010). Under low levels of relative humidity, within colonies, honey bee workers try to increase humidity by various means including nectar water evaporation and water collection (e.g. Human et al. 2006). Caged bees exposed to high temperature have been noticed to increase water uptake (Free, Spencer-Booth 1958). herefore, the integration between temperature and relative humidity is very important for honey bee activity. Not all honey bee races respond in the same way to thermal stress or even relative humidity levels. Hence, the success of honey bee races to occupy speciic regions is the overall result of an adapted response to ecological stresses. Here, two honey bee races were studied (Yemeni honey bees, Apis mellifera jemenitica, bees adapted to harsh conditions of Saudi Arabia, and Carniolan honey bees, Apis mellifera carnica, bees adapted to normal conditions) to investigate the impacts of various temperature and relative humidity levels on survival, tolerance and body water loss for these two races as well as to identify diferences in their tolerance ability. Materials and methods Material he research was performed at the Bee Research Unit 133