Ecological interactions: Survey of pathogens in relation to ovary development for bumble bee queens in Maine and Southern California

     Worldwide, bumble bees are known for their essential role as pollinators. However, some of these populations are drastically declining. Our understanding of the causes is still developing, but pathogens appear to play a critical role. In early spring, solitary bumble bee queens emerge from diapause with undeveloped ovaries. Queens must then develop their ovaries and find a suitable nest site where they can lay their eggs. Unfortunately, solitary queens are susceptible to infection by a variety of pathogens that can interfere with their reproduction and survival. For this reason, it is essential to identify what pathogens are present in queens and whether they directly impact ovary development and/or the ability to find nests and initiate colonies.
     We surveyed 151 bumble bee queens of eight different species for parasites, collected in Maine and California. We observed that 13% of Maine queens served as a host to the castrating endoparasitic nematode Sphaerularia bombi. Within these queens, all infected B. ternarius showed signs of castration by having undeveloped ovaries, whereas an infected B. perplexus queen exhibited ovary development. In comparison, no California queens were infected by S. bombi. One was parasitized by Nosema bombi, and all of them showed evidence of ovary development. This survey examines some of the most common parasites affecting queens during a crucial solitary life stage. Our findings add to our understanding of parasite prevalence in this pollinator system and their relationship to the processes of ovary development and nest establishment in wild bumble bee queens.