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nafex - Re: [nafex] European Apple sawfly

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  • From: david.maxwell@dal.ca
  • To: Steve <sdw12986@aol.com>, NAFEx <nafex@lists.ibiblio.org>
  • Subject: Re: [nafex] European Apple sawfly
  • Date: Tue, 12 Jun 2012 14:48:20 -0300

I'm not sure how successful you will be with spreading tarps. The eggs hatch
around petal
fall, and the first instar larvae gnaw on the skin, leaving the
characteristic winding trail. Then
they chew into an adjacent fruit, penetrate to the core and dine there,
shedding their skin and
becoming a second instar. This in turn chews its way out and penetrates
another fruitlet, and
so on for up to 5 instars. At some point they manage to abort the fruit so
it drops. Your tarps
would work well in catching these drops, but you need to maintain them for up
to a month or
more, as the EAS larvae are chomping on the fruit above over an extended
period, and the
fruit will drop over an equally extended period. But you are correct in
thinking that a physical
barrier is a good idea - once the fruit is on the ground the larva crawls out
and burrows into
the ground (about 5 cm./2 inches deep), and forms a cocoon, emerging next
year as an
adult. There is a wasp, Lathrolestes, which lays its eggs in the cocoon, but
Vincent & Belair,
(I think it was), reported that they don't kill enough EAS to provide
adequate control. There
are also a couple of beneficial nematodes which have been tried. Again,
while they kill a
substantial proportion, more than enough remain to cause major damage. Trying
to get them
with an insecticide sprayed into the ground is I think not likely to work -
you would have to kill
all living things to get the EAS. The only point at which commercial growers
seem inclined to
try to intervene is at the first instar, when the larva is chewing on the
skin of the first apple.
They aim to poison the skin, and kill off the larvae before they manage to
migrate into the
next fruit. (Obviously, once they are into the second fruit, insecticides
sprayed on the outside
aren't likely to do anything.)




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