Chapter 8

Application of Pesticides:

1. Use pesticides to supplement physical, agricultural, or natural methods of control.

2. Apply pesticides in a manner that offers minimal hazards to nontarget organisms, man, and the environment.

3. Use pesticides to treat only those specific sites CHEMICAL CONTROLwhere mosquitoes are present. OF MOSQUITOES

4. Apply pesticides selectively to the proper life stage of the mosquito (some adulticides may Chemical control of mosquitoes continues to be most effective against the early stages of play a major and integral part in most mosquito control larval development, while others are more programs. The application of insecticides generally effective against later stages of development). yields rapid mosquito reduction and may be the only

5. Apply pesticides in accordance with federal practical measure that can be taken to suppress and state laws and regulations and in massive mosquito populations as well as epidemics of compliance with specific instruction on the mosquito-transmitted diseases.label READ THE LABEL. The use of pesticides to control pests increased

following development of DDT in 1944. Principal Advantages of Pesticides:Achievement of dramatic results encouraged the

dependence on chemicals in all pest control 1. Mosquito control is often obtained rapidly and operations, including organized mosquito control

dramatically. programs. During the last 15 to 20 years, questions 2. Potential epidemics of mosquito-borne have been raised about the heavy dependence on

diseases can be averted or terminated. pesticides and their effects on the environment. 3. Mosquito populations that persist despite other Pesticide laws have been passed restricting the use of

control efforts (i.e., biological control) may be certain pesticides and requiring more emphasis on controlled with chemicals. integrated control. The establishment of pest

4. Economic benefits derived from adulticides annoyance thresholds for man and domestic animals applications often offset the costs. enables mosquito control programs to provide

effective control without overkill, thus reducing the Principal Limitations of Pesticides:amount of chemical usage in the environment.

1. Chemical control is temporary and must be Principles of Proper Insecticide Usage repeated frequently.

2. Pesticides may present toxic hazards to man Pesticides are toxic to living organisms some and the environment.

to animals, some to plants, and some to both. They 3. Some pesticides may cause unsightly stains or must be used with care and in accordance with damage automobile finishes and other prescribed procedures, allowing control of target pests surfaces.without causing significant damage to non-target 4. Specialized equipment and skilled personnel organisms or the environment. Accordingly, pesticide are required for the proper application of some users must carefully follow instructions for proper adulticides.usage as stated on the label. 5. Pesticides are expensive and costs continue to

rise.Selection of Pesticides and Equipment: 6. Pesticides resistance may develop within the

mosquito populations after prolonged usage.1. Pesticides must be labeled for the intended use. 7. Pesticides may reduce predator populations 2. Material should be readily available and that feed on mosquito larvae and adults.

reasonable in cost.3. Pesticides should be easily formulated. Types of Insecticides4. Appropriate equipment for pesticide application

must be readily available and in good working Chlorinated Hydrocarbon (Adulticides):

order.Of the chlorinated hydrocarbons, DDT is the best

56

known; others include benzene hexachloride (BHC) water, thus increasing it's wetting of the end of the air and its gamma isomer, lindane, as well as aldrin, tube of the mosquito larva and pupa. This, in turn, kills dieldrin, endrin, heptachlor, and chlordane. DDT was the larva or pupa by suffocation (drowning). “Golden the first massively used chlorinated hydrocarbon Bear” and BVA are two commonly used petroleum pesticide and, during almost 60 years of use, this distillates; while Arosurf MSF and Agnique MMF are insecticide made possible tremendous strides in commonly used monomolecular films. The controlling or reducing the incidence of malaria in vast advantage of these surface control agents is that they areas of the world. However, the persistence of DDT quickly kill all aquatic stages and have little or no in the environment, the development of resistance to residual effect. The disadvantage of monomolecular DDT by some insect populations, and the fact that it is films is that dried vegetation and floating debris tends stored in animal fat, led to its being banned for use in to absorb the product. Sustained winds can prevent the United States in 1972. However, DDT is still used the proper spread of monomolecular films across the in a number of other countries. At the present, no water surface.chlorinated hydrocarbons are in general use in Bacterial Larvicides: In the late 1970s a mosquito control programs in Louisiana. larval pathogen, Bacillus thuringiensis var. israelensis

Organophosphorus (Adulticides): Some (B.t.i.) was isolated from a desert in Israel. Bacillus is organophosphates are widely used in mosquito control a spore forming bacteria that is toxic to mosquito programs. They are variable in toxicity and larvae when ingested. Bacterial larvicides (B.t.i.) are persistence, and, within limits, most can be broken available for use in liquid, wettable powder, sand, down to nontoxic components in mammalian body briquets, pellets and granular formulations. tissue, and they are otherwise generally biodegradable. Inorganic Adulticides: All adulticides The most commonly used organophosphates are belonging to this group have at least one common malathion and naled. characteristic the molecular makeup of the compound

Botanicals (Adulticides of Plant Origin): does not contain any carbon atoms. The other Plant materials furnish some of the most widely known adulticides discussed previously have carbon atoms. and the safest insecticides. The most common At one time, inorganic adulticides (e.g., arsenical botanical adulticide associated with mosquito control compounds such as Paris Green) were used quite is pyrethrum. Pyrethrum is the principal household commonly, but now they are rarely, if ever, used in insecticide in many aerosol “bombs” and insect sprays. mosquito control.It produces a quick knockdown of many insects. Its high cost limits its use in wide-area mosquito control programs. Insecticide FormulationsPyrethroids (Synthetic Botanicals e.g., dimethrin, permethrin, resmethrin and phenothrin) are generally Usually insecticides must be mixed with one used as adulticides. They have the disadvantage of or more other substances to make them safe and easy being toxic to fish if misapplied. They may be used by to apply. This mixture of the active and inert individuals within homes as well as by organized ingredients is called a pesticide formulation. mosquito control programs. Formulations are discussed in detail in the EPA guide,

Insect Growth Regulators (Larvicides): “Applying Pesticides Correctly, a Guide for This is a class of larvicide that stimulates cuticular Commercial Applicators,” which is distributed by the inhibitors within the mosquito's body that in turn Louisiana Cooperative Extension Service. Therefore, disrupts the normal progression of the life cycle. The only a brief description of formulations commonly result is that the exoskeleton of the larva or pupa fails to used for mosquito control is given in this chapter.form properly, thereby preventing complete emergence in the larva-pupa molt or pupa-adult molt. Dry or Solid Formulations:IGRs are also referred to as juvenile hormone mimics. Currently, five s-methoprene formulations are sold 1. Insecticidal Dusts These consist of an inert under the trade name of Altosid. carrier, such as talc or pyrophyllite, and the

Surface Control Agents (Larvicides): These insecticide (active ingredient) that is usually in chemicals are Monomolecular Films (alcohol) or the range of 1-10% of the total weight. Although Petroleum Distillates (mineral oil) based liquid dusts are usually low in cost, easy to apply, compounds that kill mosquito larvae and pupae when nonstaining, and nontoxic to vegetation, they are applied as a surface film to breeding habitats. The rarely used in mosquito control. Poisons in dust mode of action is to reduce the surface tension of the form are generally not absorbed through the skin

57

of man, but may be dangerous i f Liquid Formulations:inhaled. Dusts do not adhere well to vertical

1. High Concentrates (Solutions) These are surfaces such as walls and are easily removed by winds and rain. They are unsightly in the special formulations consisting of pesticides home and have been replaced, for the most diluted with an oil to contain not less than 1.5 part, by sprays and aerosols. pounds of active ingredient (A. I.) per gallon.

2. Wettable Powders (Suspensions) Wettable In mosquito control, they are often used in ULV powders, prior to being mixed with water for application for control of adult mosquitoes. application, look like dusts. Unlike dusts, they This formulation allows the pesticide to stick to contain wetting agent in additions to the objects and target organisms.insecticide and inert ingredient. Wettable 2. Emulsifiable Concentrates (EC) These powders are not commonly used in mosquito formulations contain an insecticide, a control. They are not suitable for ultra low petroleum carrier, and an emulsifying agent that volume (ULV) applications and leave an permits the formulation to mix well with water. unsightly residue. Some larvicides are When diluted, emulsions need little agitation available as wettable powders and one and can be used as a residual spray both drawback is that they must be agitated while outdoors and indoors. They can also be used as applied. aerosol sprays for adult mosquito control.

3. Granules Granular particles are much larger Caution should be used when applying EC's as than those of dusts and wettable powders and they can damage some plants and stain certain are formulated on some porous carrier material surfaces.like clay or ground corncobs. The carrier 3. Aerosols An insecticidal aerosol is a fine spray material may have the pesticide coated on its with droplets ranging from 0.1 to 50 outer surface, or the pesticide may be absorbed micrometers in diameter. The finer aerosols into the material itself. Granules are remain suspended in the air for an extended commonly used as larvicides. Sometimes period, killing insects by contact. Droplets of granules are encapsulated (coated with a slowly 5-15 micrometers in diameter appear to give the dissolving material). As the coating dissolves, best control in outdoor applications against the pesticide is slowly released, ensuring the mosquitoes.presence of the toxicant in the larval habitat for an extended period. This formulation is Selection of Proper Equipmentgenerally used when excessive plant growth is present in the larval habitat. The selection and use of proper equipment for

4. Briquets Briquets are similar to granules but mosquito control will ensure that adulticides are much larger and they come in a variety of sizes dispensed to the target accurately, efficiently, and and shapes. They slowly dissolve and release a safely, with minimal contamination to the sustained amount of larvicide. Briquets are environment or adverse effects upon man. Four key normally applied to shallow depressions in no- factors should be considered when selecting adulticide flow or low-flow water conditions (i.e. application equipment:woodland pools, catch-basins, etc.).

5. Pellets Pellets are like briquets in that they 1. Each piece of equipment should be large slowly release a larvicide and offer control for enough to do the job, but not so large as to be up to 30 days. Pellets can be applied by hand, difficult to operate. Simplicity of operation and truck, or airplane and can treat a wide variety of ease of maintenance should be key factors in habitats (i.e. containers, woodland pools, flood making a selection.plains, etc.). 2. The equipment should combine durable

6. Sand sand can be used to create on-site construction and efficient design. Poorly granular formulation by combining liquid designed and poorly constructed equipment larvicide products with sand. Sand may do great harm to the public relations aspect formulations were originally developed to of mosquito control programs. In addition, the control larvae in tree canopied swamps and use of poor equipment may result in coastal salt marshes in Florida. unnecessary, and probably dangerous,

contamination of wildlife and wildlife habitats.

58

59

3. Cost is a primary factor. However, in the accomplished by using aerial application.selection of equipment, a carefully considered Power Sprayers: There are many types and overall analysis must include, in addition to sizes of power equipment available for large-scale initial cost, such factors as durability of mosquito control operations. A power sprayer usually equipment, availability of spare parts and consists of a power source (i.e., gasoline engine, repair facilities, and the degree of care that electrical), pump, chemical storage tank, and one or must be expected from workers who use it. more hoses for delivery of material. These units can

4. Safety should be a prime consideration in all be mounted on skids or permanently mounted to spray insect control applications. Hazards to the vehicles. The versatility of a skid-mounted sprayer equipment operator, the general public, and the allows it to be removed whenever the vehicle is needed environment must be considered. for other purposes. Power sprayers are used to apply

many different pesticide formulations. They are used Hand Sprayers: The compressed air sprayer for residual spraying to control resting adult

is the mainstay of most hand-applied pesticide mosquitoes, and they are used to apply larvicides (i.e., operations (Fig. 33). Usually the sprayer is a small (1- roadside ditches, woodland pools).5 gallon) cylindrical tank furnished with an air pump, Thermal Fog Applicators: Through the early hose, spray gun, and other components necessary for 1980's large thermal fog machines were used outdoors applying the pesticide. Hand sprayers are most often to kill mosquitoes by insecticidal contact much the utilized for larviciding aquatic areas of less than an same as aerosol dispensers in the home. The acre in size or for use in applying residual applications machines were generally mounted on trucks and of insecticides around the home or business produced a thick fog-like cloud dispensed downwind establishment. (Fig. 34). This method, although still applicable in

some states, is considered obsolete in Louisiana due to the high cost of petroleum diluents, the traffic hazard imposed by the “smoke screen,” and the safety of children who have a tendency to follow along behind the truck in the thick fog. Small portable thermal fog generators still have a limited use in urban areas for treating storm drain systems during disease outbreaks.

Thermal fog generators produce thick clouds of mosquito adulticide sprays. Hand-held spray tanks containing a larvicide

are used to treat small areas of standing.ULV Ground Sprayer: ULV spraying is the

Granular Applicators: A wide variety of applicator application of small amounts of highly concentrated equipment is available; this includes handheld, truck adulticide. The ground sprayer usually holds 5 to 20 mounted, and aerial. Handheld equipment may be a gallons of concentrate or formulation. It is often simple spreader or it may be backpack-powered mounted on the bed of a half-ton truck. In contrast, the sprayer. These are generally used for small areas. thermal fogger was much larger and heavier, and its Truck mounted equipment consists of a granular adulticide tank contained 25-200 gallons or more. hopper and a blower, and is used primarily to treat The unit was usually mounted on a much larger roadside ditches. The treatment of large areas (e.g. vehicle, such as a 1- to 3-ton truck.marshland, rice fields, and pastures) can be

Figure 34.Figure 33.

Great care must be taken in handling the their proper use. These label directions, as with any concentrated adulticides used in the ULV method of pesticide label, should be strictly followed.application. Spills or misuse of highly concentrated adulticides can present serious problems to humans, other animals, and the environment. Most ULV ground sprayers use a blower that delivers high-speed air to break up and transport the spray droplets to a point just outside the nozzle orifice. The prevailing winds (<10 mph) act to move the adulticide droplets across the treatment area. No wind (<1 mph) often results in poor dispersal of the adulticide and this

Aerial ULV spray applicationresults in poor control of mosquito populations in the vicinity. ULV applications use less adulticide per acre

Guidance Equipment: Global Positioning than did thermal foggers (Fig. 35). The result is less Satellite (GPS) is becoming an integrated part of environmental contamination, saving in adulticide modern mosquito control. This technology is being costs, reduction of diluents, and reduced time for used in aerial and ground spraying; also in mosquito loading or transporting adulticides. Another surveillance. GPS systems are integrated with advantage of ULV aerosols is avoidance of dense fogs computer software to improve application accuracy. such as those produced by thermal fog generators. Spray missions are recorded and can be displayed later ULV ground equipment should produce a carefully on a desktop computer. Multiple perimeters are regulated and monitored flow rate and spectrum of recorded such as spray path, date, time, temperature, droplet sizes. Usually the nozzle should be directed wind speed, and wind direction. The display of upward at an angle of 45° to ensure maximum moving maps (real time) allows for spray adjustments; dispersal of insecticide. Vehicle speed should not therefore insuring proper application of insecticide to exceed that designated on the insecticide label. Spray target areas. This equipment can be expensive, but its can be manually or automatically shutoff using new cost is usually compensated for through increased GPS systems when the vehicle is stopped.mosquito control efficiency.

Care and Maintenance of Equipment

Selection of the proper type and size of equipment is important for any application of a mosquito adulticide or a larvicide. However, the effectiveness of applications largely depends on equipment that is subjected to a regularly scheduled maintenance program and frequently calibrated to a standard specified on the product label. General directions for proper maintenance include the following points.

1. Operation of equipment according to manufacturers' specifications.

Ground ULV sprayers produce slightly visible 2. Immediately report any failure if it cannot be fogs and smaller droplets than thermal foggers. quickly repaired in the field.

3. Keep equipment clean. Empty and clean the Aerial ULV Equipment: ULV application chemical storage and delivery system

equipment is custom mounted upon or within an periodically; also clean strainers and nozzles so aircraft. In principle, the tank contains the adulticide the equipment will be ready for the next use. that is distributed under pressure to nozzles that Do not allow insecticides to stand in an idle regulate the spray. The size and configuration of machine because some are corrosive and may nozzles, system pressure, altitude, and air speed form a sludge that is difficult to remove. greatly influence the distribution and quantity of Always observe regulations regarding the safe adulticides. Chemicals registered for aerial ULV disposal of the rinse.application have specific instructions that pertain to 4. Keep machines properly lubricated.

Figure 36.

Figure 35.

60

5. Use preventative maintenance on equipment as portable hand-held sprayers and that will be out of service for long periods of sophisticated ULV cold-fog generators. The time. Cover and store equipment to avoid types of equipment used in an abatement accumulations of dirt, debris and moisture. program should be based on the nature of the

operation and the environmental character of the treatment area. Presently, mosquito Methods of Applicationcontrol districts in urban areas rely on truck-mounted ULV sprayers as the primary method Larviciding: The term “larviciding” is used to to control flying adult mosquitoes. Trained describe the procedure of applying insecticides to kill personnel are essential to maintain and operate immature mosquitoes (larvae and pupae) in the water. these machines to ensure proper droplet size In order to help preserve the susceptibility of mosquito and flow rate. species to insecticides, the same class of material

2. Aerial application Application of should not be used both as a larvicide and an adulticide, adulticides from aircraft is employed to treat especially against the same species.large and/or inaccessible areas quickly and thoroughly. Aerial spray operations must be 1. Ground Application Larviciding by hand is carefully controlled at all times since effective usually restricted to breeding areas that are too application is dependent upon the care and small for aerial treatment and inaccessible to precision with which it is carried out. Aerial vehicles. Ground larviciding is normally spraying results primarily in control of adult performed with petroleum oils, monomolecular mosquitoes in flight at the time of application. films, insect growth regulators, and/or other To obtain uniform coverage of an area, careful formulations using biological agents (e.g., observance of planned flight patterns, B.t.i.). Ground larviciding by truck is normally altitudes, air speeds, and air temperatures is restricted to roadside ditches and other breeding essential. Aerial applications for mosquito areas. Also, larvicide equipment may be control are usually conducted at altitudes mounted on 4-wheelers or other all terrain below 300 feet. Operations at excessive vehicles for control in remote locations.altitudes or in high winds can cause 2. Aerial Application Determination of the need misapplication of adulticides, resulting in for aerial spraying involves knowledge of the insufficient chemical reaching the target area. target species (including life history and Altering air speed, nozzle diameter, or behavior) and delineation of the infested areas. pressure will change the rate of application, Aerial larviciding is utilized for larger and more spray pattern, and swath width. Weather (high remote breeding areas. Liquid and solid (i.e., winds, thermals, low ceiling, and low granular, sand) formulations are the materials of visibility) may limit the use of aerial spraying. choice. Most aerial larviciding can be Early morning (dawn) and, particularly, late conducted during the daytime.evening (dusk) hours are the most effective times to utilize aerial spraying. Wind speeds Adulticiding: The term “adulticiding” is used to are usually lower at these times. Air describe the procedure of applying adulticides to kill temperature inversions are greater in the flying adult mosquitoes or those adults resting in morning and facilitate droplet placement. And vegetation, buildings, or similar harborage. Ground too, the late evening and early nighttime hours and aerial application of adulticides normally take are periods of greatest mosquito flight activity. place in the evening and night; they are targeting the Because aerial application is expensive, costs flying adult populations to attain the greatest control of modifying, equipping, and operating effects. This time period helps avoid flight activity of aircraft should be weighed carefully against non-target insects. Applicators should remember that the cost and efficiency of ground control this is the most visible form of control. Adulticiding is before a spraying program is undertaken.not a long-range substitute for such permanent

measures as drainage, land filling, water management, Insecticide Application Requirements and good sanitary practices.

1. Ground Application Controlling adult Some insecticides and some application mosquitoes by means of ground application methods are more effective against a particular life involves a wide range of equipment types such stage of the mosquito; therefore, chemicals and

61

application technique should be chosen accordingly. lethal dose is acting on the mosquito Insecticides are used generally to control either larvae population. Again this is in effect treating all or adults since these are the most vulnerable stages in generations while the formulation is active.the life cycle of the mosquito. 4. Application to All Life Stages: Selecting

An important consideration in applying an mosquitoes in both the larval and adult life insecticide involves the location of the mosquitoes. stage by using adulticides with the same mode Since many mosquito species rest at or near ground of action on all life stages. level in sheltered situations during the day, they are 5. Treat All Generations: Using insecticides much more vulnerable to treatment during the night routinely instead of when there is a problem when they are flying (i.e., exposed). Humidity, exposes all generations to the toxicant. This temperature, wind velocity, and moonlight may be does not allow for susceptible genes to thrive critical factors in determining whether or not certain in the population. mosquito species are more active at a given time. 6. Treat All Habitats: Treating every habitat

regardless of if it is producing large numbers of mosquitoes selects all generations and exposes Resistance to Insecticidesall life stages to the insecticide.

With the availability of different insecticides The best way to avoid the development of for mosquito control, there exists a responsibility to

resistance in a population is to refrain from using one use them wisely in order to prevent the mosquitoes method of control continuously in a limited area. from developing resistance. Resistance is a change in When a high percentage of control is repeated for response to selection by toxicants that may impair many successive generations in a restricted area (i.e., a control in the field and is genetically controlled. Three closed gene pool), resistance may result. Developing main types of resistance occur in mosquitoes, resistance is usually first detected when adulticides physiological, altered target site and behavioral which formerly yielded satisfactory results cease to do resistance.so. There should be routine testing to detect changes in susceptibility before resistance of this level occurs. 1. Physiological Resistance: The ability At this point it may be difficult and take years for the through physiological processes to withstand a population to recover. toxicant after it has entered the body.

A routine resistance-monitoring program 2. Altered Target Site: A change in the target would include routine testing of populations. The site so the insecticide can no longer act upon number and time of populations tested in a given area the target.will vary depending on the species. For example weak 3. Behavioral Resistance: The ability through fliers such as Cx. quinquefasciatus should be tested protective habits or behavior to avoid lethal from many areas within a district while strong fliers contact with a pesticide.such as Ae. taeniorhynchus or Cx. salinarius can be sampled from fewer locations.There are several things that can lead to the

Test methods will vary depending on development of resistance. Any one by itself of adulticide of interest. The simplest adulticide test is combination of the following can cause resistance to the CDC Bottle Bioassay. This test uses time develop in a local population.mortality data and measures a discrete phenomenon. The bottle bioassay measures the time it takes for an 1. Single Class of Insecticide: Using a single adulticide to get to its target site and work on that target class of insecticides or insecticides of different site. Anything a mosquito develops to delay or classes that target the same site (i.e. prevent the adulticide from working will be detected in organophosphates and carbamates). (Is this one this test as an increase in the time it takes for the mode or two?)mosquito to die. This test is much more sensitive in 2. Long-Residual Action: Insecticides that are detecting resistance than more traditional dose constantly in the environment especially at mortality testing. With this test you can detect lower than optimal rates can quickly select for changes in susceptibility before you see a change in resistance. In effect this acts to treat all control in the field. The bottle bioassay is much generations during the life of the adulticidequicker than dose mortality testing. Results can be 3. Slow-Release Formulation: Over time these obtained within a couple of hours.formulations have less active ingredient to

release and can create a situation where a sub

62

Testing for larvicide resistance is more complex because today's products work over long periods of time. For example with methoprene, an IGR, the effects of exposure on 1st instar larvae may not be seen until the mosquitoes attempt to emerge from the pupal stage. For this reason the best method of testing for resistance to larvicides is to use dose mortality data. Larvae are exposed to a series of different doses and mortality is scored 24 to 72 hours later. The doses that killed 50% (LD50) and 95% (LD95) are calculated. Changes in the LD50 and LD95 are then examined as a ratio. The higher the ratio, the more resistance is present.

While we know what actions will select for resistance, work is still needed to determine the best way to help a population recover. One method to delay the development of resistance is to use rotations of different chemicals, i.e. let the population recover from a particular insecticide by using another insecticide with a different mode of action for part of the spray season. Once resistance to a particular insecticide is detected, control strategies that avoid or reduce use of that insecticide should be used. Basically, following a good Integrated Mosquito Management plan will go a long way toward managing resistance.

Figure 38. Ground barrier application Figure 41. Granular larviciding

Figure 40. Handheld ULV sprayer

Figure 39. Granular backpack application

Figure 37. Aerial ULV spray application

63