6.3.1. Honey bee intra-hive relative humidity requirements

Humidity within a colony can also be influenced by honey bees, albeit to a lesser extent than temperature (Human et al., 2006). Similar to temperature, relative humidity can differ among areas of a colony (Human et al., 2006), but also fluctuate substantially because of breathing events that exchange stale air at optimal humidity with air at ambient humidity (Southwick and Moritz, 1987). Relative humidity within honey bee colonies (among frames and not within capped brood cells) is typically between 50 and 80% (Human et al., 2006; V. Dietemann, pers. comm.), and when given a choice between a range of relative humidities (i.e. 24, 40, 55, 75, and 90%), honey bees showed a preference for 75% (Ellis et al., 2008). The OECD (1998) recommends relative humidity to be between 50-70% for laboratory testing of acute oral toxicity of chemicals.