Subject: [Tweeters] Tent caterpillars & ecology
Date: Jun 27 18:03:32 2012
From: treesyes - treesyes at gmail.com


The following article, by Marianne Edain of Frosty Hollow Ecological
Services, is a really fine explanation of the role of tent
caterpillars in their ecological context. It was first posted by
Drewslist, on Whidbey Island.


Tent Dwellers of the Northwest Woods

Once upon a time there were ancient forests of enormous Douglas firs
and Western red cedars in the Puget Trough. There were Red alder
present near streams and wetlands, and in the openings where the
occasional giant tree came crashing down, but they were not
particularly common. One of the species native to these forests was
the tent caterpillar. It ate mostly Red alder leaves and converted
the vegetation into compact packets of fairly intense fertilizer.
Those packets (the polite term is ?frass?) provided a shot of
nutrients to the surrounding conifers. Good system.

Then white folks settled the area and cut down the
conifer forests. Nature abhors a vacuum and filled a lot of that bare
ground with a band-aid: the quick growing Red alder. We ended up with
large areas of alder where formerly there had been conifer forest.
Given enough time (say 50+ years), Douglas firs would grow up among
the alders, top out over them, and slowly shade out the shorter lived
alders. Tent caterpillars, which had formerly been a pretty small
component of the forest system, took advantage of those large areas
of alder to explode their population. The exploding population ate
the leaves off the alders, which allowed sunlight down to the forest
floor where the little Doug firs were struggling along, at the same
time as it delivered a great big jolt of fertilizer in the form of
all those frass pellets. Even with the system out of kilter, the tent
caterpillars were performing a very useful re-balancing service. And
because they only produce one generation per year, they rarely
actually killed any trees. They came, they went, and the trees
produced another set of leaves.

The only fly in this ointment is that the tent
caterpillars also like to munch on almost everything in the rose
family - like your apple, cherry, plum, peach, apricot, and pear
trees. A lot of people want things all neat and clean, and they reach
for the pesticide spray to kill those nasty tent caterpillars. Not
good. Counterproductive. Does more harm than good.

The caterpillars go through 5 stages called ?instars.?
When they first hatch out they form those lovely tents in the trees.
As they go through the stages they wander farther and farther from
the tent in search of leaves. Eventually they migrate down the trunk
of the tree where they were hatched and search for another high place
where they will pupate. That will produce a brown moth who will lay
eggs which look like a blob of grey styrofoam wrapped around a stem,
and the whole process will begin again next year.

There are several things which nature does to control the
caterpillars without any help from us. The most useful is a virus
(Polyhedrosis). One day the world is crawling with caterpillars. The
next day all you see are dead bodies draped all over the trees. And
that?s the end of the invasion. The other thing you see is bright
white spots, usually on the forehead of the caterpillar. This is the
egg of a wasp (kids love this part). The egg hatches and the larva
burrows into the caterpillar where it eats it from the inside out. By
the time it is ready to emerge there?s just the shell of a
caterpillar. When you pick up a tent caterpillar it will whip its
head back and forth. This is its way of trying to avoid the wasp
laying an egg on its head.

In most cases the caterpillars cannot kill your trees so
the thing to do is nothing. If you really can?t stand them, the best
thing to do is to use plain old water. Get one of those nozzles that
makes your hose act like a fire hose and just hit those tents. The
spray should knock them out of the tree. If you feel vindictive, you
can then pick up the tents and burn them, but you really don?t need
to because you?ve destroyed the caterpillars? home and they don?t
know what to do next. If you have a particularly vulnerable young
tree, you might want to wrap the trunk with cloth on which you then
smear sticky stuff (you can buy this at the garden store). Just
remember to remove the cloth after the caterpillars are gone.

Bottom line: the tent caterpillars are working to re-
balance our out of balance ecosystem. They don?t know when to stop,
so just hose them out of your fruit trees.
No need for any toxics.

- . - . - . - . - . - . - . - . - . - . - . - . - . -

Marianne Edain
Whidbey Environmental Action Network
wean at whidbey.net
www.whidbeyenvironment.org


Tina Cohen, Certified Arborist #PN0245A
Northwest Arborvitae
206-789-3283

PNW ISA Certified Tree Risk Assessor #194
Member American Society of Consulting Arborists
Registered Consulting Arborist #473

http://www.tinacohen.com/




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