The Month of June’s Work for Milkweed Pollination

The month of June has been nothing but frantic.  For the first three weeks of June, I was out in the field for the majority of the day.  While I was there, we had multiple protocols in action at the same time.  Most of the day was spent doing pollinator observations and video recordings.  For each pollinator observation, I started with a fresh, unopened umbel.  I bagged them to prevent premature pollination.  Once the umbels had opened, which usually took about two to three days, we could begin the observation.  I would record information about the milkweed itself (its height, location, and proximity to other milkweed) and the focal umbel (number of flowers, location on the plant, color of flowers).  I would then take off the bag, and distance myself about ten meters away from the plant and started the stopwatch.  I would wait 30 minutes, recording each pollinator’s arrival and departure time.  For the first five visitors to the umbel, I paused the watch and counted all the pollinia that had inserted and removed.  After the thirty minutes was up, I moved onto the next umbel.  The purpose of these pollinator observations is to quantify how efficient pollinators of milkweed are by using pollinia transfer efficiency (PTE), which is the ratio of pollinia inserted to pollinia removed.  Since I had data for the number of pollinia inserted and removed, I will be able to determine PTE for the different pollinators that we have observed.

In addition to these in-person observations, I also did video recordings.  The set up is very similar: choose an umbel (does not need to be bagged beforehand) and record information about it and the milkweed.  Then, I would train a video camera on the umbels, and record the umbels for thirty minutes.  Unfortunately, I am unable to determine PTE from these videos.  However, these videos were useful in creating a more informed list of pollinators that have been seen interacting on the milkweed umbels.

Through both of these observation types, I have noticed some interesting behaviors expressed by some of the insects.  The umbels appear to be a very good location for a specific beetle, the soldier beetle, to find a mate.  This makes sense; the beetles are nectar foragers and often encounter the opposite sex while on the umbel.  While mating, the soldier beetles will remove pollinia while moving about the umbel.  There was also a butterfly, a great spangled fritillary, that seemed to use the umbel as a place to sun itself (as a anecdote, the butterfly did not like sharing its space, as it actively and aggressively kicked off all other insects, including bees, off the umbel).

The summer continues to get hotter as we transition to the next phase of the experiment.  We will be looking at herbivory done by the red milkweed beetle and see if that affects pollination.  I will go into more detail about that next time though.  Until then, make sure to drink plenty of water and wear sunscreen (more of a note to me, but it’s generally good advice).