Honey bees (Apis mellifera) are key pollinators, playing a vital role in ecosystem maintenance and stability of crop yields. Recently, reduced honey bee survival has attracted intensive attention. Among all other honey bee stresses, temperature is a fundamental ecological factor that has been shown to affect honey bee survival. Yet, the impact of low temperature stress during capped brood on brood mortality has not been systematically investigated. In addition, little was known about how low temperature exposure during capped brood affects subsequent adult longevity. In this study, capped worker broods at 12 different developmental stages were exposed to 20°C for 12, 24, 36, 48, 60, 72, 84 and 96 hours, followed by incubation at 35°C until emergence. We found that longer durations of low temperature during capped brood led to higher mortality, higher incidences of misorientation inside cells and shorter worker longevity. Capped brood as prepupae and near emergence were more sensitive to low-temperature exposure, while capped larvae and mid-pupal stages showed the highest resistance to low-temperature stress. Our results suggest that prepupae and pupae prior to eclosion are the most sensitive stages to low temperature stress, as they are to other stresses, presumably due to many physiological changes related to metamorphosis happening during these two stages. Understanding how low-temperature stress affects honey bee physiology and longevity can improve honey bee management strategies.
Many species of high-altitude plateaus tend to be narrowly distributed along river valleys at lower elevations due to a limitation of suitable habitats. The eastern honeybee (
Apis cerana
) is such a species and this study explored the effects of long and narrow geographic distributions on honeybee populations. Genetic differentiation and diversity were assessed across populations of the southeastern Qinghai-Tibet Plateau. A total of 492 honeybee samples from eight sampling sites in four valleys were analyzed for the genetic differentiation and diversity of 31 microsatellite loci and mitochondrial tRNA
leu
-COII fragments. The following results were obtained: (1) Microsatellite genetic differentiation coefficients (
F
ST
) ranged from 0.06 to 0.16, and mitochondrial
F
ST
estimates ranged from 0.18 to 0.70 for different sampling sites in the same valley, indicating genetic differentiation. (2) Honeybees in adjacent valleys were also genetically differentiated. The
F
ST
of microsatellites and mitochondria were 0.04–0.29 and 0.06–0.76, respectively. (3) Likely a result of small population sizes, the observed genetic diversity was low. The observed impedance of honeybee gene flow among valleys increased both genetic differentiation and population numbers in the Qinghai-Tibet Plateau. This study contributes significantly to the current understanding of the mechanism underlying population genetic differentiation and highlights the potential effects of utilizing genetic resources that are subject to the ecological conditions of the long and narrow geographic distributions of plateau-valley landforms.
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