Mites on Blue Orchard Bees

A few years ago, I had a job working as a scanning electron microscope (SEM) technician for some bee biologists.  They were looking at how well the blue orchard bee (Osmia lignaria) pollinated almond orchards in California.  At the time, colony collapse disorder (CCD) was starting to cause problems and the Almond Board of California was worried about the impacts the bee losses would have on their billion dollar a year crop.  That’s right – California almonds rake in over a billion dollars each year, and it’s all thanks to bees.  Honey bee colonies are shipped to California from all over the country to pollinate almonds, over a million hives in all.  In fact, nearly half of the commercial hives in the US participate in almond pollination in California!  Needless to say, increases in CCD worried almond growers because fewer bees meant lower yields and decreased profits.  The Almond Board was therefore very interested in using native bees to supplement honey bee pollination, and they funded the project I was involved in.  The goal: to determine if the blue orchard bee was an effective almond pollinator species so that they could supplement and/or replace honey bees in the event that CCD continued to decimate their populations.

My part of the project was to use the SEM to 1) determine how pollens from different almond varieties differed (i.e., the structure of the pollen) and 2) to determine whether the blue orchard bees were visiting more than one tree variety, apparently an essential component of almond pollination, by identifying the pollen types they carried.  I spent hundreds of hours looking at pollen from flowers of various almond tree types and bees that had been captured in almond orchards after being allowed to pollinate flowers.  Basically, I spent hundreds of hours looking at this, over and over again:


Almond pollen, Nonpareil variety. The pollen grain is the wrinkly thing in the middle. The little blobby things in the upper left are fungus or some other junk.

I’m not going to talk about the results at all here because they haven’t been published yet and the information belongs to the USDA, but I did want to talk about one thing I discovered during the project: mites!

There are mites associated with a lot of bees.  The varroa mite is likely involved in CCD in honey bees and causes all sorts of problems.  Other bees have other kinds of mites.  (Check out this fabulous website if you want to see just how many bee-associated mites there are!)  The blue orchard bees apparently have these:


A mite on a blue orchard bee

I was so excited when I found these on the bees! Lots of the bees I looked at had mites on them.  And, if they had any mites at all, they typically had lots of mites:


Mites on a blue orchard bee. There are 7 in this picture!

I looked into the mite-Osmia connection and discovered that these mites are almost surely Krombein’s hairy-footed mite, or Chaetodactylus krombeini.  This mite is really interesting!  First, the mites like the ones  I found on the blue orchard bees are a specialized stage found in some mites called the hypopus or deutonymph.  Because they are immature, they only have 6 legs, not the 8 legs typical of their arachnid brethren (they get the last pair when they become adults):


Mite on blue orchard bee, view of the bottom of the mite

The hypopus is a funky life stage in the mite groups that have it.  Hypopi don’t have definable heads and have no mouthparts, so they don’t feed.  However, they do have giant claws on their legs that are used to grab the hairs of the bees.  If you click on the photo above and look at the tips of the legs (four in the upper right of the photo and two curled up closer to the back), you’ll see the claws.  These claws are necessary because the mites hitch rides on the bees to move them from place to place!  (This lifestyle is called phoresy, and the hypopus is a phoretic stage in this mite.)  Without the claws, they wouldn’t be able to hold on very well.

The mites are hitchhikers as hypopi and generally do not harm the adult bees in this stage.  Once they are taken back to the nest, though, the mites climb off the bees and infest the nest cavities.  There, they feed on the eggs or larvae of the bees or the pollen store left for the bee larva by its mother.  In either case, these mites are a bit of a pest in this species and cause serious damage or death to immature bees.  However, they are also a native pest species and have been associated with these bees for a long time.  Considering the blue orchard bee is still around, the relationship seems to be working out so far!

So the mites are interesting biologically, but I’ll admit that I wasn’t excited about that at all at first.  I only learned it when I was writing up my report anyway.  I was initially more interested in the smashing good looks of these mites!  Look at how cute these little guys are:


Mite on blue orchard bee

All those little wrinkles!  And the stubby little legs!  Adorable!*  Plus, it was exciting to look at one species and find another hidden on it.  Discoveries like these are part of why I enjoy working with the SEM so much.  Science is just so cool!

* I am willing to concede that I am horribly weird for thinking a bee parasite is cute, but I can’t help it.  :)


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