Amber Slatosky, 2013

Idaho State University

Prevalence of parasitism and size of parasites in torpid bumble bees found away from their colony

The causes of declining populations in bumble bees are manifold, from climate to disease and infection. Understanding the natural sources of limitations in colony size can help inform our understanding of how those limitations are influenced by anthropogenic processes. Bumble bees encounter many threats while attempting to acquire resources to provide for their colony, including attack from parasitoid flies (Diptera:Conopidae) that uses bumble bees as hosts in which to rear their offspring. The larvae of conpid flies have been implicated in causing workers to forage less efficiently, remain away from the colony for longer, and ultimately not return at all. Parasitoids are responsible for significant levels of early mortality due to behavioral change and physical harm in worker bumble bees as reported by researchers throughout Europe and North America and as a consequence may be limiting growth in colonies and have been found in anywhere from 5%- 70% of field-collected bumble bees. The wide range of activity reported for parasitoid conopid flies and the possible high incidence at sensitive times in the colony cycle leads to an interest in understanding more about the effects of parasitism on bumble bee behavior. Normally, worker bumble bees return to their colonies at dusk and return to foraging after dawn. However, in June 2013, large numbers of bumble bees were observed remaining at floral resources overnight. During the months of June and July, these bumble bees were collected and dissected determine if this behavior may be caused by the presence and size of their parasitoid. Comparisons were made between the larvae of conopids found in those bumble bees foraging normally and those found in bumble bees exhibiting this unusual behavior. The size of conpid larvae was found to be strongly tied to the state (foraging normally or torpid), foraging age and species of the bumble bee.

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