Adult control programs are necessary in disease situations such as encephalitis-stricken areas and in areas where a high density of pest mosquitoes occurs. The larger the area treated, the more successful the control. Adult mosquito populations can be temporarily reduced to less annoying levels. Ultra-low volume application generally is regarded as the most efficient adulticiding method.
Ultra-Low Volume Application
Special nozzle adaptations make it possible to break up undiluted, specially formulated insecticides into microscopic droplets that give effective coverage for adult mosquito control. These kinds of applications are known as ultra-low volume (ULV), ULV non-thermal, cold fog or ULV aerosol. For every 50 percent decrease in the droplet diameter of a set volume of insecticide, the spray surface area is increased eightfold. Such application techniques make it possible to effectively use very low application rates of insecticide. A comparison of malathion ULV rates for selected uses is given below:
| ounces/acre | |
| Mosquito Control | 0.7 |
| Cattle Feed Lots | 8 |
| Peas | 8 |
| Green Beans | 8 |
| Blueberries | 10 |
| Pasture and Range Grass | 12 |
| Alfalfa | 16 |
| Cherries | 16 |
The droplet size of the pesticide must be checked according to the manufacturer's recommendations. Records verifying compliance with label specifications must be kept for a period of three years.
Ground ULV application is usually done at 10 mph, using a swath width of 300 feet. Because the primary activity period for most mosquito species is during the evening (sunset) or just before sunrise, adult mosquito control by ULV and thermal fog is most effective when done during these periods when there is no wind.
Aerial application of mosquito adulticides is recommended only in extreme cases. These may include encephalitis epidemics or severe numbers of pest mosquitoes. In such cases, a ULV adulticide application is the method of choice because it will bring about an immediate reduction in the number of adult mosquitoes. This is especially important during an epidemic of EEE or SLE. Newly hatched mosquitoes will be virus free at least until their first blood meal. Killing off the older infected mosquitoes breaks the disease transmission cycle. Some insecticides labeled for ground ULV application are given in Table 2.
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Table 2. Area Ultra-Low Volume Application by Ground Equipment for Adult Mosquito Control (Follow Label Directions and Safety Precautions) |
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| Insecticide | Formulation | Flow Rate Per Minute (Average Vehicle Speed) | Remarks |
| chlorpyrifos* (Mosquitomist One ULV) (Mosquitomist 1.5 ULV) (Mosquitomist Two ULV) |
13.62% S 19.36% S 24.6% S |
3.88 to7.75 oz.(10 mph) 2.7 to 5.3 oz. (10 mph) 4 oz. (10 mph) |
For application only by public health officials and trained personnel of mosquito abatement programs. This product is toxic to fish, wildlife and birds. Apply this product only as specified on the label. |
| chlorpyrifos + permethrin* (ULV Mosquito Master 412) |
12% + 4% |
4.5 to 18 oz. (10 mph) |
This product is toxic to birds and wildlife and is extremely toxic to bees, fish and aquatic organisms. Do not apply directly to water or contaminate water when disposing of equipment washwater. |
| malathion (Fyfanon) |
95% C |
2 to 4.3 oz. (10 mph) |
Do not apply during heavy bee activity. Car finish may be spotted if droplet size is too large or application is improper. If exposure occurs, wash car immediately. |
| naled (Dibrom) | 85% C |
6 to 12 oz. (10 mph) |
Use the low vehicle speed at the recommended rate to penetrate dense vegetation. Use a dilute solution of two quarts of the 85 percent concentrate in soybean oil or HAN to make a five gallon solution. Car finish may be spotted. To prevent serious corrosion, spray equipment should be rinsed thoroughly after application. |
| permethrin + piperonyl butoxide (Biomist)* | 3% + 15% RTU 1.5% + 7.5% RTU 12% + 60% C 30% + 30% C |
3 to 18 oz. (10 mph) 6 to 18 oz. (10 mph) 1 to 3 oz. undiluted (10 mph) 1 to 3 oz. undiluted (10 mph) |
Do not apply these products within 100 feet (30 meters) of lakes and streams. These products are extremely toxic to fish. Do not apply directly to water or wetlands (swamps, bogs, marshes, and potholes.) Drift and runoff from treated areas may be hazardous to aquatic organisms in adjacent areas. Do not contaminate water when disposing of equipment washwaters. These products are highly toxic to bees exposed to direct treatment on blooming crops or weeds. Do not apply this product or allow it to drift to blooming crops or weeds while bees are actively visiting the treatment area. |
| pyrethrins + synergist* | 3% C 5% C |
6.66 to 7.50 oz. (10 mph) | Apply when temperature is 75°F or less and upwind of area to be controlled. Dilute as recommended on the label. |
| resmethrin + piperonyl butoxide* (Scourge) | 18% + 54% C 4% + 12% S |
May be diluted (10 mph) 3 to 18 oz. (10 mph) |
Apply when air currents are 2 to 8 mph or less and upwind of area to be controlled. Dilute as recommended on the label. |
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*To be applied only by licensed, certified pesticide applicators. C=Concentrate, RTU = ReadytoUse, S=Sprayable |
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Thermal Fogging
Fog can be effective as a space treatment against adult mosquitoes. Mix the insecticide in oil (kerosene-type oils, fuel oils, diesel oils and other base oils suitable for insecticide use) and apply in late evening, at night or early morning when the air is calm (less than 5 mph). Do not fog during daylight hours. Fogging is effective as a contact application with no residual effect. Frequent applications are needed during heavy adult mosquito migrations. Calibrate machines according to manufacturer's recommendations or to deliver 40 gallons per hour traveling at 5 mph to treat a swath of about 300 feet. If labelling directs otherwise, then follow product label recommendations. Operate in a manner so the fog drifts with the wind through the target area. Some insecticides labeled for thermal fog application are listed in Table 3.
| Table 3. Thermal Fog for Adult Mosquito Control (Follow Label Directions and Safety Precautions) | |||
| Insecticide | Formulation | Amount of Formulation to Use | Remarks |
| chlorpyrifos* (Mosquitomist One) (Mosquitomist 1.5) |
13.62% S 19.36% S |
9 gal. per 91 gal. oil 6 gal. per 94 gal. oil |
Apply a 300 ft. swath, from a speed of 5 mph, at a rate of 52.5 gallons per hour. For application only by licensed public health officials and trained personnel of mosquito abatement districts and other public mosquito control programs. |
| malathion (Fyfanon) |
95% C |
3.9 to 5.2 gal. per 96.1 to 94.8 gal. oil |
Deliver 40 gal./hr. at 5 mph, 300 to 400 ft. swath. Test oil solubility and sludge to prevent clogging valves of thermal fog machine. Cosolvents or sludge inhibitors may be needed with some oils. Car finish may be spotted. May be toxic to certain species of fish in shallow water. Highly toxic to bees exposed to direct treatment. |
| naled (Dibrom) |
85% C |
3.1 qt. per 99 gal. oil |
Deliver 40 gal./hr. at 5 mph, 300 to 400 ft. swath. Rinse spray equipment after application to prevent corrosion. Car finish may be spotted. |
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*To be applied only by licensed, certified pesticide applicators. C=Concentrate, S=Sprayable |
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Residual Spraying
Residual sprays are applied in water or oil, using mist blowers, pump sprayers, power backpacks or hand sprayers. They are designed to remain active for several days to several weeks, but environmental factors such as rain, high temperatures or exposure to strong sunlight may reduce their longevity. When applied to foliage, the rate of plant growth may also influence the efficacy of residual sprays. Residual sprays can be applied as barrier treatments to tall grasses, weeds, shrubs, fences, and other harborages surrounding parks, playgrounds, residences, or even subdivisions to help reduce adult mosquito populations. For best results, target areas just before the period of maximum use.
Mist spraying can be particularly useful because large areas can be treated. In some cases, it can also be used for larvicide application. Mist spraying is the application of a very fine mist of insecticide in water. The fine droplets settle out faster as a mist than as a fog or aerosol. Mist spraying should be done early in the morning or evening, when wind velocities are less than ten mph. Avoid direct application to parked cars, trailers, watercraft, dwellings, and other nontarget objects. Car finishes may be damaged if spray droplets are not washed off immediately. Some insecticides labeled for residual spraying are listed in Table 4.