Subject: [Tweeters] introduced species
Date: Sep 9 22:48:23 2005
From: Allyn Weaks - allyn. at tardigrade.net


On 8/9/2005, Guy McWethy wrote:

>The most popular plant in my yard for the birds is
>probably the Bitter Cherry

That's my birdiest plant too, so far. But it's nothing to do with the
cherries--at least not directly. My bitter cherry is about 10-11 years
old now, and this is the first year it's managed to mature any cherries
at all, maybe all of a dozen. The first year or two after it started
flowering, I was disappointed that all of the young fruits aborted. I
though it might need a cross pollinator, but my yard isn't really big
enough for two of them. Then I noticed little holes in the aborted
fruits. I cut some open, and found frass but no critters. Eventually
I found a sawfly larva (a hymenoptera), and once I started looking more
systematically, I found a lot of them, one or two per cluster. Every
cluster I could see was effected.

I still haven't properly IDed the sawfly (haven't been able to raise
any adults), but it's likely a relative of a midwestern one that goes
for pin and choke cherries, Hoplocampa lacteipennis. Once upon a time
U. Saskatchewan had a good article about them on the web, but
unfortunately it's vanished now. Anyway, what I've been able to see
matches Hoplocampa: the adults lay eggs in the flower buds, and the
larvae hatch as the fruit starts to form. The larvae crawl from fruit
to fruit in the cluster, eating the developing seeds. The fruit turns
brown and drops off. The critters overwinter as pupae in the soil.
I've seen ants catch the larvae as they go from fruit to fruit, and I
expect that they're vulnerable to birds at that time too; they don't
move very fast. They sometimes let their back ends hang a bit outside
of the fruit as they get bigger, too.

But the plot thickens. A couple of years afterwards, while cutting
open attacked fruit to show someone, out popped tiny black waspy shed
pupal cases, along with all the sawfly frass. I spent most of that
afternoon cutting open fruits, and eventually found a fresh sawfly
larva with an extra little larva attached to it. Parasitoid wasp at
work! I was able to hatch out an adult wasp, and got a 3 mm long black
wasp, possibly a braconid. A couple of years after the wasps arrived,
the sawfly incursion was noticeably reduced--many fewer early abortions.

But I still didn't get any fruit. Turns out that later in the year,
the fruit flies arrive. Little black flies with paintings on otherwise
transparent wings. The adults lay eggs in the almost developed fruit,
and the larvae eat the fruit. So far everything that escapes the
sawflies is gotten by the fruit flies. But I have confidence that
something will eventually arrive to help control the fruit flies, quite
likely a different parasitoid wasp. The dozen surviving cherries this
year could be chance, or could be evidence that the next wave has
begun--I need to start cutting open more fruits next year, somehow I
forgot this year. 10 years or more may seem a long time to wait for
nature to take her course--but it's short compared to the lifetime of
even the short-lived bitter cherry. Besides, it's not as if there's
nothing to do or see in the meantime!

As for the birds, cherries are nice food for a day or two. But this
way, at least three bug species have a shot at becoming avian
protein--year 'round if you consider overwintering stages. And that's
not counting the aphids (and eaters of aphids--hoverfly larvae, ladybug
alligators, lacewings), leaf rollers, inch worms, spiders, ants, mites,
all of which think that bitter cherry makes a great home--until they
get gulped. Satisfied customers: chickadees, bewick wrens, bushtits,
orange crowned warblers, butter-butts, wilson's warblers, warbling
vireos (I think), ruby crowned kinglets, hummingbirds, both rufous and
annas, towhees, some unidentified migrants. If I were actually a
birder, I'd likely be more observant and have a longer list :-).

(Photos of some of the characters in the play:
<http://www.tardigrade.org/natives/cherrysawfly.html>)
--
Allyn Weaks allyn at tardigrade.net Seattle, WA Sunset zone 5
Pacific NW Native Wildlife Gardening: http://www.tardigrade.org/natives/
"A proud member of the Reality-Based Community"