What Bumblebees Do When You're Not Looking

Figure 1. Miniaturized radio transmitters attached to bumblebees.
(a) Transmitter attachment on a Bombus terrestris individual kept in a glass tube with opened gauze where the transmitter is fixed with superglue. (b) Nectar collecting individual of Bombus terrestris on Phacelia flower having a transmitter attached. (c) Bombus terrestris individual with attached transmitter, foraging on red clover (Trifoliumpratense).

Can you imagine being able to track a single bumblebee over the course of a day? German and Danish scientists accomplished this impressive feat. So what do those bees do all day?

Mostly they rest.

How did these scientists accomplish such a feat? They attached tiny radio transmitters using superglue!

Transmitter attachment

We fitted transmitters to three (presumably young) Bombus hortorum queens, to one B. ruderatus worker and to four B. terrestris workers. For transmitter attachment, bumblebee individuals were put into a glass tube where one end was closed with gauze and the other end closed with foam (Figure 1a). The gauze was then partly opened with scissors so that dorsal parts of the bumblebee body were accessible but the animal was still fixed in the glass tube (Figure 1a). Collected individuals were fitted with small (200 mg) radio transmitters (Advanced Telemetry Systems, Isanti, MN, Series A2405, antenna length shortened to ca. 3 cm) on the dorsal upper abdomen using minute amounts of a combination of eyelash adhesive (DUO Lash Adhesive, American International Industries, Commerce, CA) and superglue (Instant Krazy Glue, Elmer's Products, Inc., OH). To keep transmitter weight to a minimum required the use of a small battery, limiting the transmitter life to a period of about seven days. We initially tested attaching the transmitter to the dorsal thorax of bumblebees, a method we previously found worked successfully with orchid bees [16]. However, bumblebees with transmitters attached in this way showed unbalanced flight behavior and we consequently abandoned this attachment method.

Where and when did they do the study?

Study time and area

The study was conducted between June-29 and July-5 2009 at the 'Bee Marie' conservation meadow in the vicinity of the Max Planck Institute for Ornithology at Möggingen near Radolfzell, Lake Constance region, Germany (8°59â²52E and 47°45â²55N latitude). The study area is a rural landscape mosaic composed of villages, meadows, fields, hedgerows and forest patches. Bumblebees were caught and transmitters were attached at the study site ('Bee Marie' conservation meadow).

What did they observe?

Figure 5. Detailed movement trajectories of one Bombus hortorum individual (bee 1, see Table 1) followed over a time period of >12 hours (within 2 days) with 3 continuous tracking periods.
Trajectory 1 (yellow line, order from 1a to 1c) is the first tracking period from 1-3:45 pm (165 min), starting from the study site (black square) after transmitter attachment on the first day (June-30). Trajectory 2 (blue line, from 2a to 2j) is the second tracking period from 8:45 am to 2:55 pm (370 min) on the following day (July-1), and trajectory 3 (red line, from 3a to 3e) is the third tracking period in the afternoon of the same day from 4:25-7:50 pm (205 min). The inset shows the percentages of total time spend for three different behavioral categories (resting, foraging, and moving). Note that the bumblebee rested for long time periods (>45 min) on a pear tree (105+80 min), a walnut tree (95 min), and a flower stalk (60 min + subsequent overnight stay). Flight times between points were rather short (usually <1 min).

It's interesting that they are moving only 5% of the time; the remainder of the day is spent resting (55%) and foraging (40%). Perhaps the next step towards understanding how bees utilize their environment and their behavior is to attach tiny video cameras - but the technology is not quite there yet.

They conclude:

Outlook

We found bumblebee individuals of B. terrestris, B. hortorum and B. ruderatus to fly successfully with transmitters of 200 mg which suggests that space use of large-bodied bumblebees (e.g. large workers or queens) can be studied with radio-tracking methodology. However, compared to the body size of bumblebees (workers 40-600 mg, queens up to 850 mg) current transmitters are still sufficiently large and heavy (200 mg) that they have been shown to affect foraging behavior, are likely to affect flight performance and/ or energetics and so might have fitness consequences for bumblebees. Future technological advances are likely to reduce transmitter weights further and hence will open up exciting avenues for studying flight behavior and movement paths of rather small-sized insect pollinators. This could have important implications for conservation and agriculture, especially for assessing ecosystem consequences of pollinator declines. We also see great potential for better understanding the basic biology of bees, e.g. the spatial behavior and requirements of queens, when searching for males, nest locations or hibernation sites.

This study was published in the journal PLoS One; you can read the full article here.