Seasonal Honey Bee Colony Performance and Health in Hawai'i

Abstract

The European honey bee (Apis mellifera) is among the most abundant pollinator species and the most widely managed insect in the world. In temperate areas, honey bee colonies experience large fluctuations in population throughout a year without becoming completely dormant. Numerous studies conducted in temperate regions focus on those seasonal changes and examine colony performance and overall health; however, there is little known about colony dynamics in Hawaii, where in spite of more stable ambient temperature and less pronounced seasons, there are notable changes in colony strength across the year. Hawaii does not have extremes of cold winters and hot summers, and the average daily temperature variation is small (around 3 ℃). Hawaii however, has large variations in rainfall patterns both at the regional level, especially when windward and leeward areas are compared, but precipitation also varies throughout the year. The subtropical climate of the islands is part of what makes year-round beekeeping possible in Hawaii. The Hawaiian islands are also a unique place to conduct research because the bees are 100% pure European stock, with no hybridization with African bees, as is the case in the southern U.S.The overall objective of this dissertation is to describe the seasonal growth patterns of honey bee colonies and examine possible health fluctuations under Hawaii’s climate. The results from this work contribute to basic knowledge for beekeepers, not only in Hawaii but also in other tropical areas with similar climates. Four objectives are covered in this dissertation. First, this work examines how foraging activities change across different parts of the year and how queen replacement events impact foraging. The data confirm that there were seasonal trends in colony growth in Hawaii and that the growth pattern could also be different between years, possibly due to the El Niño and La Niña phenomena. The climate in Hawaii allows for colonies to attempt queen replacement, whether it is through swarming or supersedure, during the majority of months of the year. Both swarming and supersedure led to a decreased exiting foragers per minute (EF). In contrast, the proportion of pollen foragers (P%) increased after supersedure but dropped after swarming. The degree of change in EF and P% during a swarming or supersedure event were found to be linked to its initial EF and P% before the queen replacement happened. Second, a supplemental feeding experiment was conducted for the first time in Hawaii to examine the potential benefits to colonies and local beekeepers. The results showed that colonies that received supplemental food began to grow larger than control colonies by the end of the feeding period. Most interestingly, the colony strength and larger population benefits dervided from feeding carried over to the post-feeding period. Colonies that were being fed produced nearly twice as much honey compared to the control group at the end of the study. In addition, control colonies showed a higher deformed wing virus level than the fed group. Third, climate data were used to make connections with seasonal colony growth. The analysis showed that besides temperature, daylight duration was the main trigger that impacted the colony's seasonal growth in Hawaii. Fourth, two master DWV variants, A and B, were examined at both colony and apiary levels across different months in 2018 and 2019. This study showed the prevalence of DWV-B had increased since the 2016 study. DWV-A was still dominant at an apiary level in this study; however, some colonies could already be characterized as DWV A+B mix or even DWV-B only. And finally, this study showed DWV-B had a seasonal change in both viral load and prevalence, providing a perspective on the dynamic nature of DWV master variants. Overall, the findings in this dissertation help to better understand the seasonal activity and health of honey bee colonies in a sub-tropical environment. This work provides valuable data to beekeepers in Hawaii and will contribute to the improvement of the overall colony conditions in Hawaii, both from a biological and economic perspective. The emerging of DWV-B in this study apiary also showed that there are rapid evolutionary changes between the varroa mite, the honey bee, and the DWV compared to the other parts of the world.