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Re: CULT-Borer

Things would actually be more complicated and take much longer than just
one or two seasons.  As Ian points out, what would have to be done is:

1. Find a suitable parasite.  This is by no means certain, and given the
generally low economic impact of the iris borer, such information may not
exist in the literature.  To find a parasite would require an extensive
search in the field for parasitized larvae or pupae.  The life history of
the parasite would then have to be worked out, a process that could take

2. For laboratory tests, you would have to develop ways to culture iris
borers in the laboratory and hope for multiple generations so that it would
not take forever to build up a population and run the tests with the

3. Laboratory tests would have to be followed by field tests, to determine
the effectivenss of increasing parasite populations.  Many attempts at
doing this with other pests have not worked out because the release of the
parasites had no perceptible impact on the pest population.

4. Methods would have to be developed to raise very large numbers of the
parasites, and I mean VERY large numbers.  Typical releases of parasites
for biocontrol number in the tens of thousands.  Of course this could be
far less for home gardeners.

5. The economics of the situation probably would not justify a commercial
interest.  There simply aren't enough iris growers in the effected area to
make it worth while.  For commercial growers, spraying would remain cheap,
easy and effective.

Having said all this, I still agree with Ian that it would be a very worthy
project for AIS support, especially the early stages of such research into
basic borer biology.  The borer is our main iris pest and we seem to know
surprisingly little about it.  There are now reports of borers not only
from British Columbia, but from as far west as Iowa and Wisconsin, and as
far south as South Carolina.  There is no reason not to believe that as
iris growing becomes more popular, the borer will slowly spread.

For the time being I will continue to advise hand controls for low
infestations (cleaning up debris, squashing borers that have just begun to
move down the leaf fan) and the use of systemic insecticides for heavy

Bill Shear
Department of Biology
Hampden-Sydney College
Hampden-Sydney VA 23943
FAX (804)223-6374

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