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[Narrator:] This woman is space spraying.
She is applying a mist of insecticide that will kill the flies and mosquitoes that it contacts.
It is immediately effective, but it offers only temporary control.
Other flies and mosquitoes will enter the house and the operation must be repeated.
This too is space spraying, but on a larger scale and out of doors.
Here the insecticide may be applied in either of two forms,
as a mist of tiny droplets that drift slowly downward,
or as a fog, a blanketing cloud that swirls through shrubbery and between houses.
In considering outdoor space spraying,
it is important to realize that the majority of flies and mosquitoes remain within 25 feet of ground.
This might be termed the insect zone, and it is this region that must be treated to achieve maximum kill.
Mist applicators are simple in their principle of operation.
A fan forces a high velocity blast of air past the nozzles.
The insecticide is injected into this air blast,
which breaks the liquid into fine droplets and projects them out as a mist.
There are several types of mist applicators available, some of which project a fine aerosol spray.
Most of the larger machines can be rotated in a full circle.
Also, the nozzle can be directed from side to side.
Here, mist is being projected directly at fly attractants in an alley.
Where there are no alleys, the mist is directed in a high arc over the houses,
to drift slowly down through the insect zone.
The speed of this downward drift is important, and is governed by the size of the droplets.
If they are large, the mist will fall too rapidly.
A fast rate of fall shortens the arc and cuts down on the width of the swath covered.
Droplets of the proper size will carry farther, producing a wide swath, and will continue to drift downward
in spite of thermals or rising currents of warm air.
On mist machines, droplet size is regulated by the velocity of the air blast,
the choice of nozzles, and the weight of oil used,
heavier oil producing coarser droplets. With fog, fine droplet size is desirable.
As with mist machines, several types of fog generators are available,
most of them operated from trucks, although some types are portable.
A typical thermal generator will illustrate the principle of operation.
In this machine, air and gasoline are pumped into a combustion chamber and ignited.
The expanding hot gases pass through the fog head at terrific velocities.
The insecticide is introduced into the stream of gas and is atomized into fog.
Contrary to the application of mist, fog is directed along the ground,
where it swirls around buildings, blanketing the insect zone.
Since fog is composed of exceedingly fine droplets,
it is easily affected by thermals and light breezes which will quickly carry it out of the effective area.
For this reason, fog should be applied at night or in early morning or evening when the air is quiet.
To measure the effectiveness of space-spray treatment,
it is important first to make an appraisal of the fly population by the grill method,
or of the mosquito population by trapping.
Continued routine sampling during the spray program will indicate the effectiveness of the treatment.
For most effective application, the equipment should travel at about five miles per hour,
and mist directed downwind.
With proper droplet size this will produce a swath 100 feet or more in width.
Care must be exercised in treating residential districts.
Oil mist may burn foliage and spot automobiles.
Therefore fog is frequently used in neighborhoods having expensive landscaping.
But remember, fog is quickly carried away by light winds and
thermals which occur during the warm part of the day.
For best results, fog should be applied during the still hours of night, evening, or early morning,
but for photographic purposes we are demonstrating fogging technique by daylight in this film.
Commonly the city block is considered the unit of urban space spraying;
however, if costly insecticides must be used
then treatment of the entire block on a citywide basis becomes too expensive.
Under these circumstances, spot spraying may be employed.
After an insect concentration is located, spray is applied to this limited area only,
whether it be a half-block or a single backyard.
Mist machines can be used effectively for mosquito larva sightings,
directing the mist downwind so it will carry a sufficient distance,
producing a film of larvicidal oil on the water surface.
Airplane space spraying is frequently employed for wide inaccessible areas,
although airplane application is very expensive
and should be done in the early morning or late evening hours.
Commercial indoor equipment is available for use in restaurants,
but all food and dishes must be covered before spraying is begun.
It must be emphasized that space spraying depends on contact,
and has little or no residual effect.
Partly this is due to insufficient dosage, as the following demonstration will show.
Here, mist is being applied at a normal rate.
The fall of mist is picked up on a plate of glass.
This operator is applying residual insecticide to another glass plate.
When both plates dry, a comparison will show the difference:
the dosage of the mist is entirely inadequate for residual effect.
Space spraying, then, depends on contact to kill insects.
The effect is immediate, and it is useful to gain quick relief from flies and mosquitoes.
Outdoors, effective kill depends on treating the insect zone within 25 feet of the ground.
This may be accomplished by applying a mist of insecticide that drifts slowly down through the zone,
or a fog that blankets the zone and lingers close to the ground.
Space spraying is not a cure-all for fly or mosquito problems.
It has its use for quick relief, but the results are only temporary,.
However, used intelligently and in conjunction with good sanitation practices,
space-spraying is a useful tool in any fly-control program.
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