One fifth of a thimble per acre

Paul Cherubini cherubini at
Mon Nov 13 19:37:33 EST 2000

Ken Philip wrote:

> If spraying pyrethoid insecticides at low concentrations kills
> house flies but not the (smaller) fruit flies, then there is clearly a
> large variation in susceptibility among _diptera_, not necessarily related
> to size.

Good point - size is not everything, but with the extremely tiny doses
used in mosquito control only certain flies and gnats are generally 
moderately to highly susceptible. Yes, drosophila are one of the 
exceptions that are harder to kill with pyrethroids than the much
larger house flies or mosquitoes (higher dose or more concentrated dose 
needed). And tiny greenhouse whiteflies can be a challenge to control 
with almost anything except a systemic insecticide.  And I would admit 
a monarch is more susceptible to pyrethroids than a tiny indian meal moth, 
although both insects are relatively hard to kill with Malathion. (All the
above is based on 21 years experience selling and informally evaluating 
the effects of hundreds of thousands of gallons of pyrethroids)

> No extrapolations to lepidoptera can safely be made--one would
> have to conduct tests. Have such tests been made?

Yes, there are research institutions that have spent decades evaluating 
impacts of mosquito adulticides on non-target insects. I posted
a few studies earlier in the summer and those posts should be available
in the archives.

Pyrethroids also have a huge range of dosages specified
in the label directions that take into account the wide range of 
susceptibilities. For example, the labels list a dosage for the Indian
Meal Moth that is dozens of times higher than for mosquitoes, houseflies
or gnats.

Paul Cherubini


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