Impact of low temperatures on the immune system of honeybees.

Abstract

Changes in temperature resulting from climate change can impact the distribution and survival of species, including bees, where temperature may also affect their immune system. Evaluation of immune system activity is often performed by the total count of circulating hemocytes in the hemolymph. However, there are few studies on bees examining the relationship between the amount of circulating hemocytes and temperature. This study evaluated changes of circulating hemocytes in Apis mellifera hemolymph at different temperatures and development stages. Total hemocytes of bees were determined at - 8, 16, 24, and 32°C - and at different development stages - in vivo larvae, in vitro larvae, newly emerged, and forager bees. A. mellifera larvae had a greater number of circulating hemocytes compared to the other development stages (newly emerged and foragers). Additionally, temperature was an important factor explaining variation of circulating hemocytes in the hemolymph, according to principal component analyses (PCA), as the number of circulating hemocytes was greater at higher temperatures. Therefore, extreme events arising from climate change, such as variation in temperature, can directly impact the immune system of bees, both individually and at the colony level, threatening the distribution and survival of several species.