| May 14, 2001
you probably know, the West Nile virus was discovered in New York in 1999. The New York State Department of Health provides
the following information on this virus:
West Nile virus is a mosquito-borne virus that can cause encephalitis
(inflammation of the brain) or meningitis (inflammation of the lining
of the brain and spinal cord). West Nile virus is spread to humans
by the bite of an infected mosquito. A mosquito becomes infected
by biting a bird that carries the virus. You or your child cannot
get West Nile virus from a person who
has the disease. West Nile virus is not spread by person-to-person
contact such as touching, kissing, or caring for someone who is infected. Persons
50 years of age or older have the highest risk of severe disease.
of 12/31/2000, West Nile Virus has been found in all counties in New York, except Chenango. In response
to this public health threat, various county and city health departments
throughout New York State have implemented spray programs
to control the mosquitoes that carry this virus. Initially, an organophosphate
pesticide - malathion -
was used for control; but malathion is toxic
to people, so most municipalities now use other chemicals. One of the
products being used is Anvil®. The active ingredient (ai)
in Anvil is Sumithrin, a member of the pyrethroid family. It is highly toxic to honey bees, as indicated
by its LD50 value. The LD50 is the dose at which 50% of an
exposed population is killed. Sumithrin has
an LD50 of 0.06743 ug/bee (one ug =
1 millionth of a gram). A second
product being used is Scourge®. The active ingredient in Scourge is Resmethrin. It is also a pyrethroid and
is highly toxic to bees, with an LD50 of
0.063 ug/bee. Both compounds have
very short half-lives in the field.
manufacturer's internal study of Sumithrin concluded
that an application rate of 0.0674 lb ai/acre
would be damaging to honey bees. Fortunately, the actual application
rates for Anvil and Scourge will be no more than 0.0036 lbs ai/acre,
considerably below the level that the manufacturer's study indicates
would be damaging to bees. Unfortunately, some of the calculations
involved in determining if a specific application rate will be damaging
to bees are theoretical, and empirical data on which to base a recommendation
are not available. Therefore, I cannot make any guarantees about the
safety of the spray program at this time as it pertains to honey bees.
However, since the actual application rates for these compounds will
be about 1/20th of the rate that the manufacturer's study
indicates would be damaging to honey bees, I do not anticipate serious pesticide damage to honey
bees if spraying is conducted between one hour after sunset and one
hour before sunrise.
Bear in mind that health department officials have
a responsibility to balance public health concerns with environmental
ones and may need to authorize sprays during early morning and evening
hours, when mosquitoes are active. In addition, other compounds such
as Malathion (Fyfanon®), fenthion (Baytex®), naled (Dibrom®), carbaryl (Sevin®) and chlorpyrifos (Dursban®) may be used. All of these are listed as highly
toxic to bees and have longer residual half-lives than the aforementioned pyrethroids. I cannot make a general statement regarding
the extent of damage that might occur with all compounds under all
spray regimes because many factors affect the extent of the damage
a pesticide will have on bees. The key factors to bear in mind when
making your decision to protect your bees are: the pesticide's LD50 (the lower the LD50,
the greater the risk to your bees), its residual activity (a longer
residual period increases risk), the time of application (daytime applications
pose the greatest risk), and the current status of the nectar flow
(a strong flow increases risk). The actual risk is determined from
a combination of these factors. For example, a daytime application
of Malathion to flowering plants during a
nectar flow poses a very high risk to bees. Nighttime applications
of Anvil or Scourge at 0.0036 lbs ai/acre
pose considerably less risk. Contact
your local health department and ask for a copy of their spray policy.
Be sure to obtain the information mentioned above. You will have to
make the final decision about protecting your bees based on local conditions.
the risk factors combine to pose a serious risk to bees, you will want
to consider one of two options. Beekeepers with one or two colonies
can confine their bees during and immediately after a spray. If you
choose this method, you will have to confine your bees the night before
the spray takes place, and leave them shut in for 24 hours. Before
confining your bees, make sure they have sufficient space to prevent
overheating - that may mean adding an extra super of empty combs. Remove
the entrance reducer, if present, and screen off the entrance with
1/8" hardware cloth. Plug or tape all other holes in your equipment
that the bees can use as entrances, and replace the inner and outer
covers with a piece of 1/8" hardware cloth stapled over the top of
the hive. Cover the hive with two layers of wet burlap, and keep the
burlap wet while the bees are confined. Place a sheet of plastic loosely
over the burlap during the spray to minimize direct contact with the
pesticide, but remove it immediately after the spray. If your bees
are in the sun, you must provide shade. A day of confinement is all
that a colony can take without suffering damage, especially if it is
hot. Beekeepers with more than a couple of colonies will want to move
their bees out of the spray area. Be sure to contact the health department
in the county where you plan to move your bees to be sure there is
no spray program planned for that area.
you leave your colonies unprotected in a spray zone, observe the entrances
for several days after the spray takes place. If you note an unusual
number of dead, crawling or dying bees in front of your hives, call
your regional DEC office immediately and ask that a Pesticide Specialist
sample your bees to determine if the kill is due to the pesticide that
was sprayed in your area. Ask DEC for a laboratory assay to determine
if the product used to control the mosquitoes is present in your bees.
Also, report any confirmed pesticide damage to me, so that I
can determine the statewide impact of the spray programs on honey bees.
have contacted agencies in other states to learn about their experiences
with these pesticides. The staff at the Florida Department of Agriculture
Mosquito Control Program informed me that they have not had any bee-related
problems with Anvil and Scourge when using nighttime, ground applications.
Some minor damage to bees hanging outside their hives on hot nights
has been noted, but that is all. In a similar vein, colleagues in Missouri have also informed me that
they do not experience damage from pyrethroid sprays
unless the spray contacts bees hanging out on hot nights. So, that
is relatively good news.
can contact the following New York State Department of Health website
for more information on the West Nile Virus, control methods for mosquitoes,
and the various pesticides being used as part of the control program: http://www.health.state.ny.us/. You can contact the following DEC website to
locate phone numbers for your regional DEC office: http://www.dec.state.ny.us/.
am contacting the state's county health departments and asking that
they restrict any spraying to nighttime applications of Anvil or Scourge.
Also, I am asking that they consider focusing on control of larval
mosquitoes rather than the adults because larvicides are
less toxic to bees. Compounds such as methoprene and Bt are
effective against the immature stage of the mosquito, non-toxic to
people, and relatively non-toxic to bees. Local community-based programs
that focus on the elimination of breeding areas, such as old tires
and cans with water, can also have a significant impact on mosquito populations.
share this information with all members of your organization.
Professor of Apiculture
Ithaca, NY 14853
The following websites have good information on mosquito spraying: