Rates of Parasitism in Solitary Native Bees

In recent years, honey bee (Apis spp.) populations have been droping dramatically. They have been experiencing many stresses which have resulted in a wide spread phenomenon called Colony Collapse Disorder. Because honey bees are a major pollinator of our crops, this disorder is threatening to tear apart our agricultural systems. Without these systems, we won’t be finding any more fruits or vegetables in our grocery stores our our dinner tables. Consequently, there is now an increased interest in studying alternative pollinators such as flower flies and solitary bees. Although ecologist have been studying some of the groups for many years, not enough is known about them in order to use them in a commercial setting.

Osmia sp. on a nesting block
Osmia sp. on a nesting block

One group of insects that are of particular interest are mason bees (Osmia spp.). These bees are commonly found nesting in preexisting holes in logs and hollow reeds. Females will build up a cache of pollen and nectar in these per-existing holes, deposit an egg and then seal the nest (Michener 2000). However, often times parasites, such as parasitoids and kleptoparasites, will invade the nest and lay their own eggs (Wcislo and Cane 1996). The parasite egg will usually hatch before the host and eat the host egg. Once the host has been eliminated, the parasite larvae will feed on the pollen stored in the nest. Unfortunately, parasitism rates can be very high, with 15% of nests parasitized (Steffan-Dewenter and Schiele 1993). Although previous studies have looked at what factors affect rates of parasitism (Goodell 2003, Rosenheim 1990), conflicting results have emerged. Studies have reported both positive and negative density dependent rates of parasitism in solitary bees (Rosenheim 1990, Wcislo 1984).

A nesting block with a paper straw sticking out.
A nesting block with a paper straw sticking out.

Adam Groulx, the graduate student I worked with this summer, set out to untangle some of these results. We setup up two experiments to test two different factors that may affect rates of parasitism in mason bees.

Nest Density
The first experiment was aimed at seeing how the density of nests affects rate of parasitism. We setup up three sites with each site containing a low density and a high density replicate. The high density replicates consisted of two large nesting blocks with 32 nests each, attached to a single tree. The low density replicates consisted of 4 small nesting blocks with 16 nests each, attached to four different nests seperated by about 10m.

Cuckoo Wasp (a kleptoparasitic wasp)
Cuckoo Wasp (a kleptoparasitic wasp)

Resource Availability
The second experiment was aimed as seeing how the availability of floral resources affects rates of parasitism. We setup four sites with a total of 80 nests at each site. Each site was selected so that the nesting blocks were located along the margin between a field and a meadow. We applied two treatments: low and high resource availability. The low resource availability treatment involved covering all of the flowers in the field within a 25m radius with row covers. The material acted to stop pollinators from access the flowers. The high resource availability treatment did not have any covers. In order to reduce site affects, we decided to move the row covers between sites at least once.

A Resource Availability Site Covered with Row Covers
A Resource Availability Site Covered with Row Covers

Our work simply involved monitoring the nesting blocks for parasites. When we noticed that there was significant bee activity, we stood by the blocks and recorded bee and parasite behavior for about 45 minutes. We also dissected all the nests and recorded whether a nest was parasitized or not. We also took pollen samples from the first and last cells of each nest to compare pollen use with wildflower phenology.

A parasitized Osmia nest cell. The large egg is the host and the small egg is the parasite (Sapygid wasp egg).
A parasitized Osmia nest cell. The large egg is the host and the small egg is the parasite (Sapygid wasp egg).

Unfortunately field work is a finicky business. We were unable to get enough bees in the resource availability experiment to obtain adequate results. Sometimes the bees just don’t want to nest where you want them to. On the other hand, we did get plenty of bees in the density experiment blocks. This provided us with a good deal of data that is currently being worked on.

First Two Weeks at the Rocky Mountain Biological Laboratory

After many delays getting to Colorado, I finally made it to the Rocky Mountain Biological Laboratory near Crested Butte, Colorado. If first impressions really mean anything, I know that I’m going to have a fantastic time here. So far, my first two weeks have been incredibly amazing!

An Amazing Setting

The Rocky Mountain Biological Laboratory is nestled in a small valley under the majestic Gothic Mountain. Until now, I’ve only ever seen the Rocky Mountains in pictures and videos. Nothing can compare to actually being here. This place is absolutely amazing. Every morning, I wake up to see Gothic Mountain outside my window. Everything about this place is amazing: the geology and geography, the flora and fauna, the people and their research and the night time stars. The scenery is breathtaking and the research being done is fascinating. This is truly a paradise for me!

Altitude Sickness

I was warned many times before coming that I would suffer altitude sickness. I’m pleased to report that the extent of my malaise was minimal. I did have a strong headache for the first tow days, but that was it. Another major issue with working here in RMBL is the risk of dehydration. It’s pretty dry here so it is super important to consume as much water as you can. It also goes without saying that being at a much higher elevation than normal results in shortness of breath. I’ll admit that hiking to some of our research sites has left me literally breathless. BUt after two weeks, I feel like I’m improving my fitness level.

Field Work

Field work has been a lot of fun. When I arrived, the graduate student I work for and I went scouting for sites to setup our experiments. We hiked a considerable distance: 16km the day after I arrived. Finding locations was a bit of a challenge as we had many criteria. Once our sites were selected, we set about with putting up the nesting blocks in which, we hope, Osmia sp. bees will nest. Since then, we’ve been monitoring the nesting blocks for occupancy as we wait to start our observations.
I have to say that I can’t complain about my job. It’s my job to hike around the Rocky Mountains and keep my eyes open for bees (which are super cool)! This is exactly the kind of work that I’ve always wanted to do. I’m doing what I love in a place that is gorgeous. Granted, some days are long and hard, but I couldn’t be happier!

Sunday Hike to Emerald Lake

I had the day off last Sunday and decided to hike up towards Emerald Lake. I went with Adam, the grad student I work for, and Camille, an coop student working with Dr Jessica Forrest. We hiked about 7km up the mountain trails towards the lake until we were hit by a snowstorm. We were high in the mountains and exposed, so we decided to turn back and head home. Although we did not make it to our destination, we had a fantastic time.

What’s Next

So that’s what I’ve been up to for the last two and a half weeks. It’s been a lot of fun, I’ve learned a great deal and I’m supper happy to be here working. Over the next week, we will continue to check for occupancy in the nesting blocks. Once we have enough Osmia in residence, we’ll start with data collection. It’s looking like this is going to be an amazing summer!

Flying to Gunnison, Colorado

Well, it looks like the frustrations of doing field work abroad have already started. As part of my job in the Forrest Lab, I have to help out a graduate student and Dr Forrest with their work at the Rocky Mountain Biological Laboratory in Gothic, Colorado. Everything for the trip was looking great. Little did I know this morning (at 2 AM) that misfortune was coming my way. At the Ottawa airport I was informed that my flight to Washington was canceled by the US Air Traffic Controller (because the plane is too small to survive today’s wind conditions). So they flew me to Toronto and re-booked all my flights resulting in me having to stay overnight in Denver before flying out to Gunnison the next morning.

Airport reading material: Scientific American
Scientific American should keep me entertained while I wait for my flight.

Not only is this a big inconvenience, the whole situation got to be absolutely ridiculous. I was supposed to fly with another student to Gunnison. It seems that the heavens were smiling on her. We both flew to Toronto but our airline was nice enough to re-book her on another carrier’s morning flight to Denver. This was a little frustrating considering that I checked in before her and asked to be put on any other carrier that would get me to Denver on time! When I approached a ticket agent about this issue to request to be placed on the same flight, the agent told me the plane was full. That was disappointing, but I guess there’s not much I can do about it. But it gets worse. My fellow traveler informs me from within the aircraft that the flight is almost completely empty! The carrier lied to me! They said it was full! As frustrating as this is, I’m well aware that this is pretty normal. I’ve heard plenty of horror stories from other travelers and, to be honest, my situation isn’t that bad.

So…now I’m siting in Toronto waiting for an afternoon flight to Denver. Fortunately my carrier gave me a voucher for a hotel in Denver so at least I’ll get a good night’s sleep tonight.

(Happy) flying everyone!


Field Work in Gatineau Park

When I started studying biology, I was really excited to get outside and do some field work. This year, I was fortunate to get a summer job in the Forrest Lab at uOttawa. The PI, Dr Jessica Forrest, is currently working with Dr Risa Sargent  on a long-term study of the phenology of wildflowers and pollinators in Gatineau Park, Quebec, Canada. Part of my work includes helping Dr Forrest and Dr Sargent collect data for this project. I was really excited to participate on this project when Dr Forrest brought it to my attention. This was an opportunity for me to practice my bee catching skills, learn new methods of sampling bee populations and learn some of the intricacies and aspects of working in the field. So I finally got the chance to get some real field work under my belt!

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