Research and Interests
I am interested in whether or not the risks associated with conopid parasitism vary by bee species. I am also interested in further developing our understanding of the natural history of this natural enemy.
I find the intersection of parasitism and sociality fascinating. Within a social insect colony, the loss of certain members exact a higher fitness cost than the loss of others. For a colony, the loss of a worker is the loss of resources/ resource acquisition. The loss of a queen means no more workers and no daughter queens can be produced. Parasitoids in particular are fascinating because they do not immediately kill their host (like a predator would), nor do they have continual sublethal effects like a parasite would have. They exact sublethal costs that increase over time, culminating in death of the host. This system is ideal to study this type of interaction because there are multiple species of bumble bee available, and the likelihood of different castes interacting with parasitoids should vary by species.
Meet the current bumblebee colonies!
<----New addition! See my Enviroday Poster Here!
Bumble bees and conopid flies: Natural History
Bumble bees are primitively eusocial insects with an annual colony cycle. This means that unlike honey bees, they must start their colonies anew each spring. The previous season's daughter queens emerge from hibernation and found colonies. These colonies consist of the founding queen and the workers she produces. These workers gather resources while the queen continues to lay eggs that will develop into more workers. Eventually the colony will switch to the production of reproductive offspring: daughter queens and males. These queens that were produced by the colony will hibernate underground and found the next generation of colonies.
Cool things you may not have known about bumble bees:
- Workers can lay eggs, though these eggs will become males because the worker has not mated (link).
- Workers do not lose their stinger when they attack.
- There is only one species of honey bee (Apis mellifera), but there are 46 species of bumble bee in North America.
- Male bumble bees cannot sting you.
- Bumble bees can warm themselves up and fly in cooler temperatures (link).
- Bumble bees can learn! (link)
Conopid flies are parasitoids that attack a variety of insects. The particular conopid flies I study commonly attack bumble bees and will attack multiple species of bumble bee.
Conopid flies hibernate underground as pupae and emerge each summer to mate and then track down bees to serve as hosts for their immature young. They will attack bees in flight and lay an egg into the bee's abdomen. This egg will hatch and the larva will feed on the bee's internal organs until there is almost nothing left. At this point the bee, near death, will dig its own grave. Once underground the conopid larva will finish up the tissues of the bee and then pupate, ready to emerge the following summer.
Things conopid flies do to bees:
They shorten a bee's lifespan.
They change bee behavior in several ways:
They make bees less likely to forage for pollen
They make bees use easier flowers
They seem to make bees prefer cooler temperatures
They seem to cause bees to abandon their coloniesThese findings are largely the work of Paul & Regula Schmid-Hempel
The video below shows a bee that has been parasitized. The dark area I focus on is where the fly has attached so it can breathe while feeding on the bee.
The general ideas behind my work
1. Certain species should experience a selection-weak space (Schmid-Hempel, 1998- Parasites in Social Insects) for protecting their workforce relative to others. Large colonies are more resilient to disturbances, large colonies can produce more reproductives, and large colonies would need less defense. A species-wide strategy could be to produce many expendable workers and simply grow as quickly as possible. For these colonies, and for species that regularly engage in this strategy, the value of defense against parasitoids would be relatively low.
2. Some species should experience pressure to resist parasites because of the timing of when they produce their reproductive offspring. In the image above, I have lined up a chart showing parasitism rates with the timing of colony activities. The black bars represent when reproductive offspring are generally seen at flowers, meaning that the production of these offspring begins a little bit prior to the start of the black bar. For bees that are producing daughter queens during high parasitoid activity, there should be resistance to parasitoids, at least among those daughter queens. Colony sizes are also shown here, which would lead to a prediction that a species like B. impatiens should have lower resistance to parasitoids relative to species like B. bimaculatus & B. griseocollis.
How I go about exploring these relationships
Because conopid flies can have numerous impacts on bumble bee behavior, I can examine these impacts and look for species differences. I can also look at conpid fly preference by providing conopid flies with opportunities to choose between host types.
I can explore how certain behaviors are altered by conopid parasitism by watching bee behavior very closely. I do this with two methods: RFID technology and motion capture video. With RFID technology I can monitor the comings and goings of individual bees by placing an individualized tag on each bee that is read by a computer. This computer stores the times that each bee triggered a read. With motion capture technology, I can visually inspect bees for whether or not they carry pollen. I am currently working with Dr. T'ai Roulston to figure out how to also detect changes in nectar returns. I'm enjoying learning how to use 3-D printing to construct parts specific to this project.
What follows are selected slides from a presentation I gave about my RFID + Motion Capture technology.
Changes in immune system response:
Previous work at Blandy Experimental Farm has shown that one species B. griseocollis has a stronger melanization response than B. impatiens & B. bimaculatus. I am continuing this work by looking at more species of bee for their responses, including one species that is not known to become parasitized by conopid flies.
Based on this work:
- Davis, S. E., Malfi, R. L., & T’ai, H. R. (2015). Species differences in bumblebee immune response predict developmental success of a parasitoid fly. Oecologia, 178(4), 1017-1032.
Differences in parasitism rates between castes. Because some daughter queens are produced at times of peak parasitism, it is possible to examine these queens and see if they are subject to conopid parasitism. So far I have been able to determine that queens of B. bimaculatus & B. griseocollis that are produced during peak parasitism do indeed experience surprisingly high rates of parasitism.