Saturday, January 28, 2012

Giant Willow Aphids - Winter In The Willow

We don't see many insects this time of year.  Yet, here are some Giant Willow Aphids hanging out on the Curly Willow in our backyard, in spite of the cold and snow.
  These few are remnants of a big willow aphid colony that was here until a few weeks ago.  Most of them grew wings and went elsewhere to overwinter as adults.  Honestly, the ones that are left look rather dead... I even took a few into the house to try to thaw them out... unsuccessfully.  Maybe the cold and exposure had gotten to them, or maybe I just picked the wrong ones to try to revive.
   Giant Willow Aphids are large (as aphids go), grey aphids with a dorsal tubercle which look somewhat like shark fin.
Giant Willow Aphid - Tuberolchnus salignus
In the late fall, or early winter, the adults grow wings like the one pictured in the background of the photo below.

Here is a photo of the aphid colony in the beginning of December.
Notice a few of them have wings.
Colony of Giant Willow Aphids - Tuberolchnus salignus
I went out one frosty morning to get a close-up picture showing frost crystals on the willow branch opposite the aphids.
Frosty willow aphids
I thought a photo showing the ice crystals would illustrate the willow aphid's cold tolerance.  Despite the hard frosts, cold nights, and even some snow.... most of the aphids grew wings and left.
 
   Even if these remaining ones are dead, the aphid's cold hardiness is on display, because wherever the others went, it's just as cold there...just not as exposed to the wind, rain, and rapid temperature fluctuations.

   When  I first noticed the aphids feeding on our willow, the colony was quite small... see the picture below.  These aphids are reported to only reproduce parthenogenetically - that is the female gives birth to a genetically identical daughter aphid through asexual reproduction.  That means the aphids in large colony I photographed Dec 1st are all clones...genetically identical subdivisions.
   Notice the aphids were being tended by many ants which were furiously defending their honeydew supply against an onslaught of intruding mosquitoes and other insects. I counted about a dozen diptera in this photo. There is also a small parasitic wasp in the right side of the picture approaching on a branch.

  I actually noticed the aphid colony when I was taking a closer look at a cloud of insects swirling around the in the willow.  This swarm was attracted by the aphid's honeydew excretions.  The aphids produced so much honeydew that it exceeded what the ants were "milking".  The aphids jettisoned this excess honeydew, as evidenced by the wet spot on the ground (next picture) below the colony.  The ants were there feasting at this honeydew puddle as well.
 Mosquitoes and other insects were there as well... feeding on the sparkling droplets of honeydew.
   Ants take their job seriously...protecting their honeydew source.  On several occasions I watched the drama of the ants battling the honeydew seekers.  In the center of the photo below, the ants have a mosquito stretched between several guards.  Below the captive mosquito, a hungry caddisfly has arrived for some honeydew.
Seconds later the small caddisfly was captured and hauled away.
Yep, there has been quite a show going on in our willow the last few months!
Winter's cold has quieted down all that flurry of activity.
Compare the next few pictures that show the aphid colony slowly dissipating in preparation for the dead of winter.
On (left picture) Dec. 1st, the colony was about at its peak.  On Dec 18 (right picture) there were noticeably less aphids
 
By mid-January there were only a few stragglers (perhaps dead ones) left hanging around on the willow
 All the winged adult willow aphids have gone somewhere to spend the winter... perhaps to more sheltered locations in the fencerow, or the woods across the river.  Wherever they went, I expect some of them to return to our willow next summer.  Possibly even the ones that stayed on the willow will be reanimated and begin another colony.
Then...the show will go on!

1 comment:

  1. Wow Dana. What an big world in a tiny space. I love the one photo with the flying mosquito. Super post.

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