Size, temperature and bee love

The natural world is constantly changing, especially with climate change looming over different aspects of it. Humans are therefore affected, but creatures much smaller than humans are taking the brunt of the impact of climate change. Some creatures, such as the insects that pollinate food for humans, are facing critical declines. While climate change is directly impacting many different parts of an insect's life, a research group from the Republic of Korea and New Zealand focused on how climate heating impacts how buff-tailed bumblebees (Bombus terrestris), a very important pollinating insect, choose their mates, which is critical for the future of bumblebee colonies. Min Su Park, Ji Hyun Woo, Hyung Joo Yoon, Bo Yeon Kim, Kwang Sik Lee and Byung Rae Jin (Dong-A University, Republic of Korea), Steven A. Trewick (Massey University Manawatu, New Zealand) and Kyeong Yong Lee (National Academy of Agricultural Science, Republic of Korea) collaborated to examine how rising temperatures affected how males compete to attract a mate and how females choose the males they want to mate with.The researchers collected male bees and queen bees from several colonies, measured their body mass and categorized each male as small, medium or large. They then tested the insects' preferences for a mate by placing equal numbers of large and small male bees with medium-sized queens inside a mating box for 2 h, keeping track of how often the bees mated, when and for how long. In another set of mate-choice tests, Park and colleagues placed equal numbers of large and small queens with medium-sized males in a mating box for the same length of time. Having conducted the tests at a low temperature (23°C), they then repeated them at the higher temperature of 32°C to see if it would affect anything. Additionally, they checked the males' sperm count at the end of each mating session.Once the researchers had analyzed all of their measurements, they found some things that aligned with the measurements that other scientists had made previously, where body size does indeed matter for male and female buff-tailed bumblebees when looking for a mate. The team found that the largest male bumble bees (with the largest body mass) mated more than smaller male bumble bees. And when the researchers looked at how long each bee couple mated for, it took longer for the smaller male bees to complete mating and the larger males' sperm counts were higher after mating had finished. In addition, when the researchers looked at which females the males preferred to mate with, they found that large queens mated much more with large males.Interestingly, body size mattered even more in the heat. At cooler temperatures, queens mated with both large and small males equally. But at 32°C, large males mated more often and passed on more sperm to the queens, because they had higher sperm counts. Queens also preferred larger mates when it was warmer. Plus, heavier queens tended to survive winter better, so size affected not just mating but also survival. Both temperature and body mass play a key role in the act of mating, as it can really determine the fate of future bumblebees.Both large males and large queens have characteristics that would benefit them in the long run. For example, large males have a higher sperm count, which is good because it gives the males a better chance of fertilizing the queen's eggs, resulting also in success for the female with a lot of new baby bees and a successful colony. And large queens are more likely to survive through the winter, which is the first step for queens to produce a successful colony the following spring.