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.

All insects are influenced by low temperature. However, as a typical stenothermic insect, the honey bee is perhaps the most severely affected. Low temperature exposure during the capped brood stages leads to high mortality and shortened worker longevity. The impact of low temperature stress on vein development has not, however, been investigated. In this study, the eight different developmental stages of capped brood (Apis mellifera) were exposed to 20 °C for 12, 24, 36, 48, 60, 72, 84, and 96 h, and then incubated at 35 °C (the optimum temperature for brood development) until emergence. We found a total of 21 abnormal vein types, consisting of 16 types of supernumerary veins and five types of lost veins. The abnormal phenomena in the brood occurred mainly 1–4 days after capping, when the metamorphosis process from larvae to pupa occurs. Our results suggest that this metamorphosis process is critical for the development of veins, indicating it as the most sensitive period to low-temperature. In addition, we found a cross vein “rs-m” between Rs and M in the hind wing of the honey bee, which has previously been ignored due to its very short length. This study on the effects of temperature on wing venation in stenothermic insects adds to our understanding of the thermal requirements for shaping the wing vein pattern, and for predicting wing venation deformation. This also adds a new research route for the investigation of the evolutionary relationship between honey bees and other hymenopteran insects.

In the evolutionary process, honey bee populations became divergent due to geographical barriers or ecological adaptation, but to date which specific barriers and ecological isolation conditions that blocked the honey bee gene flow remain uncertain. Here, the morphometric divergence of Apis cerana was studied across southwestern China, a region of diverse topography, featuring a low-elevation basin in the east and a high-elevation mountain and plateau in the west. A multivariate morphometric analysis was conducted on 1482 A. cerana individuals from 25 sampling sites across Sichuan province. The populations dwelling in high-elevation areas with larger body sizes and darker coloration were differentiated from the eastern low-elevation basin population. Moreover, the populations dwelling in the Jinshajiang, Yalongjiang, and DaduRiver Valleys showed significant divergence. Our data indicate that the morphometric variation between the high and low altitudes, probably due to the adaptation to the integrated effects of ecological factors such as air temperature, humidity, the nectar and pollen plants, and light intensity etc. Additionally, the mountains with an altitude of more than 3300 m and a honey bee-free zone probably served as a barrier to gene flow between the river valley populations.