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Northern Territory Department of Health Library Services Historical Collection
DL HIST 614.4323 WHE 1981
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HISTORICAL COLLECTION
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DEPARTMENT OF HEALTH.all.ii
AND COMMUNITY SERVICESMOSQUITO CONTROL BY THE ULTRA LOW VOLUME GROUND APPLICATION OF INSECTICIDE
For more information contact:
NT Department of Health and Community Services Medical Entomology Branch PO Box 40596
CASUARINA NT 0811 Telephone: 22 8333
Peter Whelan
Senior Medical Entomologist
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MOSQUITO CONTROL BY THE ULTRA LOW VOLUME GROUND APPLICATION OF INSECTICIDE
Northern Territory Department of Health and Community Services
Medical Entomolsgy Branch
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1. 0
THE ULV AEROSOL
The ULV (ultra low volume) insecticide technique is the means of applying the minimum amount of liquid insecticide per unit area, compatible with the economic requirements for achieving insect control. This method has been widely tested and used for controlling adult mosquitoes and can be applied by ground equipment or from the air.
2. 0
DROPLET SIZE
In ultra low volume application the droplet size is within the range of aerosols. An aerosol has a volume median diameter (VMD) of less than 50mu ( microns) where 1 mu equals . 0001 centimetre. A mist has a VMD of 50mu to 100mu. The VMD is the number that divides the particles of insecticide into two equal parts by volume, one half containing droplets smaller than this diameter, and the other half containing larger droplets. The definition of optimum droplet size acFepted by WHO expert committee on insecticides, is a size which gives the maximum control of the target organism with a minimum amount of insecticide and the minimum amount of contamination of the ecosystem.
3. 0
IMPORTANCE OF DROPLET SIZE
There are a number of factors that influence the effectiveness of various sized droplets in space sprays.
3. 1 THE SIZE AND DISTRIBUTION OF THE DROPLETS
Two of the most important requirements for aerosols are that the droplets are small enough to provide adequate coverage to impinge upon target organisms, and that they are large enough for adequate impaction on the insect to occur. The number of spray droplets available from a given volume of spray liquid is inversely related to the cube of the diameter. That is, as the average diameter of the droplet decreases, the total number of spray droplets markedly increases. Based on these requirements, a realistic dropiet size for the control of mosquitoes from ground applicators is between 10 to 25 microns. At 45 millilitres per hectare in a 3 metre depth of air there would be 18 drops per millilitre i f all were 10 microns, and only 1. 2 drops per millilitre i f the size of the droplet was 25 microns.
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3.2 THE TOXICITY OF THE INSECTICIDE FOR THE TARGET VECTOR
The toxicity of various insecticides has been tested against various species of mosquitoes. For example, in the USA i t has been found that a single 25 micron drop of technical Malathion will kill one Aedes taeniorhynchus mosquito.3.3
THE SIZE OF THE TARGET VECTOR AND WHETHER IT IS AT REST OR MOVING IN RELATION TO THE DROPLETS
Smaller objects are better collectors of droplets than larger ones. Small insects such as mosquitoes, with many hairs and bristles and scales, are good collectors of droplets. Active flight by an insect greatly increases the probability that smaller particles will be impacted on i t s wings. If the aerosol is applied at a period when mosquitoes are actively flying, the probability of killing the insect is increased.
3.4 THE LOCATION OF THE VECTOR TO BE CONTROLLED
The location of the mosquitoes when applying the fog is important. Droplets applied from ground level must be smaller that 30 microns in biameter to prevent excessive filtering by foliage in forested areas. The denser the foliage, the smaller the droplet required to reach the mosquito in the foliage.
3. 5
THE VELOCITY AND DIRECTION OF AIR CURRENTS, ATMOSPHERIC DIFFUSION BY TEMPERATURE GRADIENTS, AND OTHER METEOROLOGICAL FACTORS
Natural air currents or winds must be relied upon to transport the droplets, so greater attention has to be taken of the wind direction when deciding where the aerosol will be applied.
Wind velocity above 13 kilometres per hour is too high for the application of aerosols as the particles are dispersed too rapidly and are not kept together as a fog. The distance of effective drift will be affected by the density of the insecticide used, the wind velocity, particles size and the type and amount of obstacles in the path of the drift.
3.6 THE METHOD OF APPLYING INSECTICIDE AND THE DISTANCE
FROM THE RELEASE POINT TO THE TARGET
The application of insecticide by ULV method using ground equipment should only be made from evening to early morning so that the treatment coincides with the greatest mosquito activity. Surveillance of mosquito numbers throughout the night by the use of various traps should be used as a means of determining the periods when ,the applications should be carried out. Applications during the day are not recommended because on warm days the air rises from the hot ground and causes the fog to move upward with the air currents and subsequently to disperse. Other weather conditions should be conducive to allowing aerosol to remain close to the ground.
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4. 0
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In particular, wind velocity should not exced 13 kilometres per hour. In a windy situation the vehicle should move at a slower speed and the length of the application area should be reduced, due to the increased dispersal caused by the wind.
In the residential area the city block would be the area treated. Fogging is commenced downwind and the vehicle travels across the wind. With light breezes the normal swath width would be up to 150 metres in open areas, and down to 45 metres in the heavily vegetated areas. The public should be advised before fogging operations so that people such as beekeepers whose hives may be in the path of the insecticide, can take the necessary precautions against the insecticide.
Access to the areas to be fogged is an important factor due to differences in wind direction and i f access from at least two sides to an area to be fogged is not provided, then provision should be made for their installation. The breeding grounds for mosquitoes near residential areas provide frequent sources of mosquitoes and i f these areas are near densely vegetated areas they can be daytime harbourage areas for mosquitoes. If the breeding and harbouring areas are fogged early in the evening, the numbers of mosquitoes invading the residential areas will be reduced.
APPLICATION OF AEROSOLS BY THE LECO HD ULV MACHINE
(This is not a recommendation for any commercial ULV applicator) The Leco ULV aerosol fogger produces a non-thermal aerosol which consists of fine droplets optimally with a mass median diameter of 20 microns, where 80% of the droplets are below 20 microns.
This droplet size i f near the optimal size recommended for ULV applications for the control of adult flying mosquitoes in both open and forested areas. The droplets remain suspended in air and the resulting aerosol fog will move through an area on prevailing breezes. Malathion insecticide has been recommended for use in this machine by the manufacturers and has been approved for use as a ground applied fog in the USA and Australia. The application of Malathion by the Leco ULV fogger has been extensively researched in the USA and other countries for i t s effectiveness in killing mosquitoes. It has been found that there are minimum effects on most non-target organisms and very l i t t l e residual effects after one day when Malathion ULV has been applied to kill mosquitoes.
5. 0 OPERATION OF THE LECO ULV FOGGER
1 . Follow the insecticide reservoirs.
preliminary tanks, fuel
Procedures of filling t~nk and checking the
the oil
2. Check all lines for any air or insectide leaks and check the seal on top of the insecticide tank.
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3. Check to see that the insecticide switch is off. Start the
4.
5.
engine of the machine and adjust engine speed to provide 30 kilopascals pressure on the gauges.
Ensure that the nozzle of the blower unit is at an angle of 45 degrees and not in front of any objects or people.
Turn the indicator
insectide to the previously from correction curves.
switch to on and adjust the ball correct flow metre reading obtained the provided flow charts and temperature
6. The recommended rate of Malathion application is 85mls/min using ULV Malathion.
7. Check the formation of the fog with a powerful torch and get an idea of the wind speed and direction from the manner in which the fog moves.
8. Proceed with the fogging operation, keeping in mind the prevailing breezes and checking periodically with a torch.
Mosquito breeding and harbourage areas outside residential areas can be fogged by applying the fog from the correct direction for drift into the mosquito breeding areas.
9. A constant vehicle speed should be maintained and whenever the vehicle is stopped, the insecticide switch should be turned to off.
10. At a vehicle speed of 16 kms per hour with 85ml/min through the machine, this will apply approximately 32ml/ha, based on a 90 metre swath width.
11. After fogging operation, the machine should be flushed using kerosene for five minutes. This is done by dipping the insecticide supply line from the insecticide tank into a container of kerosene and following the normal fogging procedures except that the insecticide tank top is loosened and the flow meter is turned up high.
12. The machine should be properly maintained, with attention to changing the oil and adequately storing the machine out of the weather.
a) Any spilt kerosene as
insecticide should be i t will effect the paint
flushed off on a machine.
b) Periodically inspect replace i f suspect.
c) When not in use loosen
rubber seal on insecticide
seal, on insecticide tank.
with
tank,
d) Store engine on compression to prevent sticking valves.
e) Do not store in open - sun has deleterious effects on hoses. Replace hoses after few years operation.
5 oo,
04
f) When not in regular use, run machine every one or two months to ensure battery remains charged or remove battery and use a battery charger every 1 - 2 months.
g) Do not force the insufficient check
flow for a-i r evident in flow lines.
gauge - locks
i f pressure is bubbles will be
13. The droplet size of a machine should be checked periodically.
The method recommended is the WHO method of waving magnesium oxide coated slides in the path of the fog and measuring at least two hundred of the droplets under a microscope.
14. Droplet size can be increased as the engine speed, and thus pressure is decreased. Droplet size can be increased as the volume of the insecticide through the machine is increased.
References
Mount, G. A., Pierce, N. W. and Baldwin, K. F. ( 1975) Droplet size of aerosols dispersed by portable and truck-mounted generators. Mos qui to News 35( 2) 195-8
Tagatz, M. E. , Effects of environments
Borthwick, P. W., Cook, G. H.
ground applications of in Northwestern Florida.
and Coppage, D. L. ( 1974) Malathion on salt-marsh Mos qui to News 34( 3) 309-15 World Health Organization (1971) Application and Dispersal of Pesticides. Technical Report Series No 465. 66pp
P. I. Whelan 1 9 81