BEE-n there, done that: will the bees come back after removal of the flowers?

Over the last few weeks, I have spent a lot of time looking at bees. I have been taking videos of bees, counting bees, observing them, and all of this almost exclusively right in the middle of the Harvey Mudd Campus (Figure 1). My name is Moira, and I am a new addition to the Social Insect Behavior Lab this semester! I am a senior Mathematical and Computational Biology major. Over the last few years, I have worked on a wide range of research projects (identifying octocoral species, the stress response in E.coli, protein relocalization in parasites), but this has been my first experience working outside on an ecology project! I grew up spending as much time outdoors as possible, and have always been fascinated by biology because of my love for nature, so it is a natural fit for me to be joining Social Insect Behavior Lab!

Figure 1: Here is a picture of me observing honey bee visitation to white sage, right next to the Shanahan Center at Harvey Mudd.

I have to admit though...I have been scared of bees for a long time. I was stung by a honeybee only once, when I was seven years old, and I think I might have remembered the experience to be a little more traumatic than it actually was. However, each day I have spent working in the Social Insect Behavior Lab has taught me how much we ought to appreciate these fascinating animals!! For example, last week Xingyao showed me how honey bees collect pollen in baskets in their back legs (check out a picture of it in Tessa's blog post!). These baskets can change colors based on what type of plant the pollen comes from, ranging from yellow to white and even blue!

My favorite thing I have learned so far about bees has to be the waggle dance though!! Because honey bees live in hive communities, communication is really important. When a worker bee is foraging for nectar, it is searching for plants where it can collect a lot of sweet nectar, and do so in an efficient way! Plants with a lot of flowers which are also rich in nectar can offer an individual honey bee great reward, but also can be rewarding for the entire hive. When a bee visits a rewarding plant, it will travel back to the hive and direct other worker bees towards the same plant, as shown in the waggle dance video linked above! Through this dance, bees can communicate both direction and distance to a plant!

Figure 2: Here a honey bee visits Salvia apiana (white sage). The honey bee is on an inflorescence, the flowering stalk of a plant and is searching for flowers rich in nectar. It is ideal for the bee when it can move along an inflorescence going from flower to flower which are rich in nectar.

Over the last few years, the HMC Bee Lab has been studying how honey bees communicate and why certain plants may be more appealing than others! Last summer, John, Matt, and Xingyao observed how honey bee visitation rates depend on plant size and other things associated with that, and found that honey bees seem to prefer plants where the flowers are more densely packed together. Specifically, their research showed that honey bee visitation rates to Salvia apiana (white sage) depends on the number of flowers per inflorescence (flowering stalks). I am interested in understanding why honey bees behave this way, and what they can gain from it. It makes sense that honey bees would prefer plants with more flowers on a given inflorescence, because when a plant has a lot of flowers close together, a bee can travel up an inflorescence, moving from flower to flower quickly while collecting a lot of nectar (Figure 2). You can see videos and read more in John’s blog post!

I am interested in the specifics of this. Does manipulating the number of flowers on a given inflorescence change the way in which a honey bee might visit a plant? I suspect that it will be more costly for a bee to visit a plant with less flowers per inflorescence, because it has to spend more time travelling from one flower to the next flower and may spend more time changing inflorescences. To figure this out, I am observing honey bee visitation to white sage before and after I change the flower density (number of flowers per inflorescence). For this manipulation, we remove about every other flower on each stem of the inflorescence. This process does not take as long as you might think, only about 5 minutes if there are two of us are working together. We collect the three following types of data before and after the manipulation:

• We record how bees move around on a single inflorescence by taking video recordings. It is tricky to capture the video of the bee visiting an inflorescence, because while some visits last well over a minute, others are only a few seconds! (Video 1)
• We record how bees move around between inflorescences by observing 20 inflorescences. We record how long a bee spends on each inflorescence, how long it spends travelling between inflorescences, and how many flowers it visits on each. It takes two people working together to try to keep track of this, using a stopwatch & a counter.
• Finally we record how the the overall number of honey bee visits to the 20 inflorescence cluster changes by watching 10 of the inflorescences for 10 minutes before and after manipulation.

Video 1: Here a honey bee moves up the flowering inflorescence. As you can tell, I have to move the camera and refocus often to follow the bee up the inflorescence. This video lets us record the time the bee spends on each flower and how long it spends traveling between flowers. This video was taken before we manipulated the number of flowers on this inflorescence.

The data that we are gathering will help us understand how a honey bee might change the way in which it visits a plant after the flower density has been changed. First, we will determine if the overall number of bees which visit changes once we manipulate the flower density. Based on last summer’s research, we expect less bees to visit when there are less flowers. From there, we want to understand why less bees are visiting and what happens when they do visit. Do they spend less time on each flower and more time travelling between flowers? What about on entire inflorescences, and the whole patch of inflorescences?

Normally, flowers are not manipulated like this during an experiment. We are interested in which plant characteristics are appealing to a bee, and this manipulation helps us determine which plant attributes will result in a bee staying for longer. Because honey bees have a really unique method of searching for plants and communicating that back to their hive, we can think about what this manipulation means for a community as well, not just an individual. If a honey bee has a greater preference for a plant, then they will choose to communicate that preference back to their hive. An interesting future project would be to document how manipulating flower density changes the way bees choose to communicate about it.

Understanding how honey bees search for plants and why bees chose to visit specific plants can be useful in a variety of settings, especially due to the importance of bees in agriculture. As Tessa describes in this blog post, domesticated honey bees are used to pollinate crops around the world, particularly in the Americas. However, bees are now facing a serious threat due colony collapse disorder. The solution to protecting bees and sustaining our current agricultural practices is not clear, but what is clear is the importance of understanding honey bee behavior. Research projects like mine help us understand how honey bees harvest resources and how that changes when those resources change, an important consideration as our landscape is altered by intensifying agriculture and climate change.