Thursday, November 21, 2013

Fall's Flying Lint

Woolly aphid-- Mark Bower
While surveying the mushrooms at Valley Water Mill (VWM), Mark Bower showed me a log with clusters of tiny 2 mm light blue winged insects.  Looking closely they even appeared to be covered in powder.  He nailed the diagnosis of wooly aphids before I could even get back to my computer.
Woolly aphids on a VWM log- Mark Bower
Many wooly aphids are natives, members of the Eriosomatinae subfamily.  In flight they have been likened to "flying mice", and are given nicknames like "angel flies", "fluff bugs", "fairy flies", "ash bugs".  My favorite is "flying lint".  Some specialize on one variety of plants while others may lay eggs for their larva on a different species than the ones adults feed upon.
Insect trash talk- Mark Bower
The wooly apple aphid is a major economic pest in orchards.  Like the cedar apple rust galls that depend on cedar and apple trees in close proximity to support their two year life cycle, the apple aphid requires elm trees for the egg and larva feeding phase while the adults attack apple trees.  Woolly aphids have a needle-like stylet mouth which they use to penetrate buds, bark, leaves and roots to suck up sap.   Many produce a sticky honeydew which then can support the growth of a sooty mold on the fruit.
Ready for take-off - Mark Bower
Many wooly aphid species are accidentally introduced invasive species.  An example is the hackberry wooly aphid, Shivaphis celti, which was found in the south in the 1990's and is now also a problem in California.    Although it doesn't damage the tree significantly, it is a pest because its copious honeydew excretions create a sticky mess which in turn feeds a blackish sooty mold on leaves and anything under infested trees..  There is a lot of hackberry out at VWM although I couldn't identify the downed log.

The reproductive cycle of these woolly aphids which use two host plant species is complex, as explained by this Bugtracks article.  Most species emerge as all females in the spring and reproduce parthenogenesis (without mating between the male and female).  They give live birth(no eggs) several times in the spring and summer on the primary host plant.  Winged forms then fly to the secondary host plant, reproduce again and eventually give birth to winged males and females which fly off to a primary host plant and mate, starting the whole process.  If you think this confuses you, imagine being the aphid figuring our your family history.

Not all wooly aphids are warm fuzzy creatures.  The larvae of the wooly beach blight aphids gather together when disturbed and poke their posteriors in the air, an aphid version of "mooning".  It looks like dancing as seen in this video.  This is no hollow threat as they are shown under the microscope to stab predators with their stylet mouth parts that are usually reserved for penetrating wood to sip sap.  I guess if you usually drill into beach trees with your mouth, penetrating a predatory moth larva is a piece of cake.

The most complete source of information on aphids isaphidsonworldsplants.

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