mosquito control and non-target organisms

[Jeffrey A. Caldwell]

Interesting paper.  I wasn't aware of  this sort of control activity, killing
adult mosquitos only.  I wonder how large the sprayed areas were; the "rebound"
of flying insects in sprayed areas within 48 hours sounds like it must've at
least partly been from an influx from the surrounding area filling the empty
niche.

Of course, I suppose new insects are constantly emerging, too.  When I had a
back injury in Texas and started going into the swimming pool late every
afternoon, I was amazed to see how many insects were constantly "raining" into
the pool [I was gathering the living insects every day from the surface of the
pool [the ones falling in while I was in it]  for something to do while
tractioning my back by staying the water.   There was a constant progression,
this species for a few days to a week or two, then that ... always changing.
Not many leps though; mostly beetles, bugs, leafhoppers, wasps, bees, flies ...
it helped me understand how the waters support so many fish, constantly
subsidized by insect food produced on surrounding lands ... fly fishing really
started to make sense.

Paul Cherubini wrote:

> Ok, lets get onto a more lep related topics like the effects of
> mosquito spraying on non-target organisms such as butterflies
> and moths in the USA. Is there any scientific evidence, for example,
> to support the NABA website claim of "disasterous" non-target impacts
> from  spraying Malathion or pyrethroid insecticides over New York City?
>
> I received the following email today from a Ph.D. entomologist that
> works for a Mosquito abatement control district:
>
> Dear Mr. Cherubini. A friend of mine forwarded to me your request for
> research about the effects of mosquito spraying on non-target organisms. I
> suggest that you get the following paper.
>
> Effects of Ultra-Low Volume Pyrethrin, Malathion and Permethrin on
> Non-target Invertebrates, Sentinel Mosquitoes, and Mosquitofish in
> Seasonally Impounded Wetlands. Truls Jensen, Sharon P. Lawler and Deborah A.
> Dritz. 1999. Journal of the American Mosquito Control Association. 15(3):
> 330-338.
>
> Dr. Jensen may be contacted at Illinois Natural History Survey, Medical
> Entomology Program, 607 E. Peabody Drive, Champaign, IL 61820.
>
> The abstract for the paper reads: Wildlife managers are concerned that
> insecticides used to control mosquitoes could suppress invertebrates on
> which wildlife feed. We assessed whether ultra-low volume (ULV) applications
> of pyrethrin, permethrin, and malathion for control of adult mosquitoes
> reduced macroinvetebrate abundance and biomass or killed mosquitofish in
> seasonal wetlands in California. Pyrethrin was applied over three seasonal
> wetlands on Sutter National Wildlife Refuge (NWR), and malathion or
> permethrin were each applied over two seasonal wetlands on the Colusa NWR.
> Three control wetlands were used per site. We measured aquatic
> macroinvertebrate abundance and biomass before and after insecticide
> application and compared survival of mosquito larvae held in sentinel cages.
> At Colusa, we also used mosquitofish as sentinels, caged adult mosquitoes
> over the wetlands to test for pesticide efficacy and drift, and sampled
> night-flying insects using ultraviolet light traps. Results showed no
> detectable reductions in the abundance or biomass of aquatic
> macroinvertebrates in treated wetlands. Larval mosquitoes showed high
> survival in all areas. All adult mosquitoes died when caged over wetlands
> treated with malathion and permethrin, but all survived in controls. All
> mosquitofish survived. Flying insects abundance decreased after insecticide
> application in both treated and control wetlands but rebounded in 48 hours.
> Results indicated that ULV applications of these insecticides to control
> adult mosquitoes are unlikely to have substantial effects upon the aquatic
> insects or fish in seasonal wetlands.
>
> These results are significant for several reasons. First, fish are extremely
> sensitive to pyrethroid insecticides (including permethrin and resmethrin).
> Mosquitofish were not affected in the above study. Permethrin is more
> persistent in the field than resmethrin strongly suggesting that resmethrin
> will have an ever lower effect than permethrin simply because resmethrin
> degrades faster and loses its pesticidal activity. Second, non-target
> insects as a group were not significantly affected. You will note that
> suppression occurred in both treated and control wetlands after insecticide
> application which suggests that something other than the insecticide reduced
> insect activity. Most important is the rebound seen 48 hours after pesticide
> application.
>
> Pesticide applications for controlling adult mosquitoes are normally made at
> night when most beneficial insects (honeybees, lady bird beetles, etc.) are
> not active. The labels of mosquito control pesticides include specific
> instructions designed to minimize contact between the pesticide and
> non-target insects. Thus, when applied according to label instructions (as
> in the above study), pesticides for mosquito control should not
> significantly affect non-target organisms.
>
> I hope this information is useful. Please contact Dr. Jensen directly if you
> have more questions about the study.
>
> With best regards,
>
> Stephen Manweiler, Ph. D.
> Metropolitan Mosquito Control District
> 2099 University Avenue West
> St. Paul, MN 55104
> phone: 651-645-9149
> FAX: 651-645-3246
> e-mail: mmcd_sam at visi.com