Chapter 7

Record Keeping

The record of any inspection should contain, in addition to the inspection data, the following basic information: inspector's name, date of inspection, and exact location. Location description, especially in rural areas, can sometimes be quite difficult. For this reason, a map with location keys can be very helpful. MOSQUITO SAMPLINGFor routine surveillance work, numbered or named AND SURVEILLANCEstations are usually established with their locations

marked on a map. Then the location description Inspection is a basic function of any organized becomes a simple matter of recording the station mosquito control program. It provides data on which number or name.all control operations are based. Indeed, without good

In wide-ranging survey work narrative inspection data, it is practically impossible to conduct descriptions are sometimes needed to describe an efficient and effective mosquito control program.locations exactly. These should be simplified While the methods of conducting inspections whenever possible. In cities, this is easy. “NW corner are many, the purpose behind the activity generally th thof lot, 15 Street and 9 Avenue” is a brief description, falls into one of two categories, “survey” and which leaves no doubt as to the location. There are “surveillance.” The term “survey” is usually applied to some areas that are difficult to accurately locate (i.e., one-time gathering of inspection data to assess a marshlands). However, maps can be subdivided into situation. A survey may cover a small or large area and numbered or named areas for easy reference. Some may be limited to one factor (such as breeding in common methods of subdividing maps involve the artificial containers) or may include many aspects of utilization of geographical features, artificial grids, or the total mosquito problem. Surveillance, on the other a combination of these to set boundaries on areas hand, is a continuing process of inspection for the which are indexed for easy reference and filing. To purpose of monitoring changes in mosquito avoid cluttering maps, the larger areas may be further populations. A good surveillance program indicates subdivided by the use of transparent overlays, again when control measures are needed as well as the employing geographical features of a grid. Once the effectiveness of the measures.area of inspection is delineated by reference to index A basic inspection program for a mosquito numbers, additional location data can be conveyed control operation usually addresses the following: most clearly by the use of cards that include a rough adult mosquito population density and species sketch of the area. In routine surveillance work, composition, rainfall and tide monitoring, and records of inspections are best kept on some type of breeding site locations. Additional inspection may be standard inspection form. Data recording forms serve required for special problems such as surveillance of a dual purpose. They promote uniformity which bird and mosquito populations to monitor makes records easier to read, interpret, and encephalitides and other arboviral diseases. Ovitraps summarize. They also serve as a reminder to the are used to collect Aedes aegypti and Ae. albopictus inspector to record all pertinent information. Of eggs for surveillance and location of breeding sites.course, surveillance that takes advantage of Global Most inspection efforts in a mosquito control Positioning System (GPS) satellites makes record operation are aimed at surveillance. Initial surveys are keeping much easier as well as more accurate, usually made to establish the need for control especially when used with a good computer program. measures, and if need is found the results of the control

measures will be assessed by subsequent inspections. Adult Mosquito SurveillanceIn order to avoid comparing dissimilar parameters, it is

necessary that inspections be consistent, both in A collection of samples should be a true method and location. For this reason, the keeping of

representation of the abundance and species clear, accurate records is as important as the data composition of an adult mosquito population present gathering itself. Records of inspections should be kept at the time of collection. Unfortunately, all mosquito with the thought that subsequent inspections may be species do not behave the same. Some are more made by someone else less familiar with the area. strongly attracted to light than others, some are active Because record keeping is basic to all inspection at night (nocturnal), some are active during the procedures, it will be discussed before specific daytime (diurnal), others are active during the twilight inspection methods.

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hours (crepuscular), some species prefer mammalian affixed to a permanent collection site for the entire blood, and others prefer the blood of reptiles and birds. mosquito season. It is powered from an electrical Add to this the fact that populations of the same species outlet. The battery-powered lightweight CDC trap is exhibit cyclical patterns of behavior (e.g., attraction to the smaller of the two and is portable for use in remote light and biting activity). It becomes evident that at areas. There are a number of different portable traps any given time, it is unlikely that any sampling method available for mosquito surveillance. Many traps have will be completely unbiased. The data for an a photo switch which turns the trap on at dusk.individual mosquito sampling must be evaluated It must be noted that light traps collect only carefully. It is only through experience and knowledge those species attracted to light. Some species are not of mosquito biology that surveillance data can be attracted to visible light, and therefore are not captured accurately interpreted. by this technique. Ultra violet (black) light used in

The following is a brief description of the conjunction with the CDC trap or the Fay-Prince trap commonly used inspection techniques to assess adult (Fig. 31) will generally increase the number and mosquito populations. species of mosquitoes caught, including those species

Landing Rate Count: With this method, not normally attracted to visible light.inspectors use themselves as bait. They record the Light traps are often supplied with carbon number and species of adult mosquitoes landing in a dioxide (CO2) to enhance their attractiveness to given period of time (usually one minute). They may mosquitoes. The CO2 source may be a small (fist-also count the number of mosquitoes approaching, but sized) block of dry ice or a cylinder of compressed gas. not landing. It is important when employing this In these cases, the addition of CO2 has been found to method into surveillance that inspectors always stand attract both greater numbers and more species of in the exact same location. mosquitoes to the traps. This is due to CO2 being a

biting attractant for adult mosquitoes. Truck Trap: The basic truck trap consists of a

large funnel-shaped frame, usually rectangular in cross-section and covered with screen wire. This structure is mounted, with the large end forward, on the roof of a vehicle. The collection container is attached to the smaller end of the funnel. The trap operates like a seine as the vehicle moves along the road. This is the most non-selective of the traps; however, some selectivity occurs because of the time of day during which the raps is operated and the height of the trap above the ground. Also, only those mosquitoes which fly in open areas along roadways can be practically sampled.

Animal-Baited Trap: This screened enclosure usually contains a stanchion to restrain the bait animal and a means of capturing mosquitoes attracted to the bait. A variety of bait animals may be used in these traps (i.e., horses, cows, pigeons, mice, et cetera). Most traps have solid walls with screen cones or baffles that allow the mosquitoes to enter through these openings but impede escape.

Resting Station: A resting station takes Figure Conducting landing rate counts of advantage of the fact that night-flying species

mosquitoes. frequently rest in dark, sheltered places during the day. A resting station may be a natural or man-made

Light Trap: This mechanical device employs sheltered situation (e.g., rotted tree boxes). In either a light to attract flying mosquitoes and a suction fan to case, the resting mosquitoes may be counted with the draw them into a container. The most common forms aid of a flashlight or collected with a suction device of light traps used in mosquito control programs (aspirator) or with a killing tube (Fig. 27). Mosquitoes include the New Jersey light trap (Fig. 29) and CDC usually found in these include Culiseta melanura and light trap (Fig. 28). The New Jersey trap is generally Anopheles spp.

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may be used to capture the larvae or to separate them Breeding Site Inspectionsfrom dark-colored water and debris such as that found in discarded vehicle tires. During the warm months, The best indication that a site produces there is a good chance of finding larvae of permanent mosquitoes is to find mosquito larvae in the water. In water-breeding species at most times.clear, shallow water over a light-colored bottom,

The presence of larvae of floodwater species is visual inspection will reveal the larvae. In most other dependent on tides, irrigation systems, and/or rainfall. situations, vegetation, debris, turbidity, and the Unless the site has undergone the proper flood-dry coloration of the larvae combine to make their cycle just prior to inspection, larvae probably will not detection difficult. In all cases, the larvae must be be present. To increase the probability of success, the collected if they are to be positively identified, and the inspection must be made soon after flooding occurs in breeding potential of the habitat assessed.order to locate larvae of floodwater mosquitoes as Collecting mosquito larvae requires a these species rapidly develop through the aquatic minimum amount of supplies (Fig. 26). The most stages.common method of sampling is by dipping. A

Sample site selection should be based on a common drinking dipper, made of plastic, is thrust into thorough knowledge of vegetation associated with the water in a swift, but careful manner so as to capture mosquito breeding habitat. This is particularly true in larvae before they can dive beneath the surface. The salt marshes where it is often difficult to determine if number caught in a dipper of water is reported as standing water is the result of daily tidal fluctuation or “number per dip.” While dipping, the person must be of recent intermittent flooding. Only the latter sites careful not to cast a shadow over the spot where the dip will produce mosquitoes.is to be taken. The shadow on the water surface alerts

With instruction and experience, the inspector the larvae of possible danger, and they will descend to learns to identify the plant species that are associated the bottom of the habitat. Pupae can descend with daily (tidal), intermittently, or permanently particularly fast and will be even more difficult to dip.flooded conditions, and also with fresh, intermediate, brackish, or saltwater situations. Such knowledge will enable a person to interpret the breeding potential of a relatively large area from a limited number of samples.

Egg Survey

Retrieving Eggs from Soil: During extended periods of drought, when larvae are difficult to locate, a search for eggs of floodwater species may be indicated to locate future breeding sites and to evaluate the magnitude of subsequent problems. This particular egg-collecting technique is a time-consuming and difficult process and is not usually employed in routine survey work. It consists of shredding clumps of soil, washing the particles through a progressively finer series of sieves and finally, isolating mosquito eggs by flotation in strong saltwater solutions. There are keys available to taxonomists to aid in the identification of eggs of floodwater mosquitoes.

Ovitrap: The primary purpose of an ovitrap is to induce container-breeding species to lay their eggs in the trap, for subsequent identification. The most

Figure Dipping for mosquito larvae widely used ovitrap is the “little black jar” (LBJ). This consists of a glass or plastic jar, which is partially

Water may be removed with a large syringe in filled with water (Fig. 25).the case of tree holes or may simply be poured out from containers such as buckets and cans. A tea strainer

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A rough textured, fiberboard paddle, strip of seed and bodies of terrain are involved are involved, GPS germination paper, or strip of velour paper, long can be indispensable.enough to extend above the water line, is placed in the jar. Container-breeding mosquitoes, such as Ae. Summaryaegypti, Ae. albopictus, and Ae. triseriatus, lay eggs (oviposit) on the paddle or paper in preference to the A good surveillance program takes time to smooth-sided jar. The paddles are periodically develop. In addition it will probably change over the removed and brought to the laboratory for microscopic years due to changes in population demographics examination. Other types of ovitraps have been within the District as well as possible additions of new developed for sampling other container/tree-hole species and diseases. Since 1985 there has been the breeding species. addition of Ae. albopictus and Ae. japonicus as well as

the discovery of West Nile Virus. However, there is simply no way to conduct an effective mosquito control program without an ongoing surveillance

system based on sound science.

Figure Ovitrap or “little black jar (LBJ)” used to detect egglaying Aedes species.

While they are not adult-sampling devices per se, ovitraps do furnish some index of adult mosquito density. Caution should be used, however, since the correlation between egg count and adult population density is not always consistent because the number of eggs laid (fecundity) may vary during the season or even over the lifetime of a single generation.

Global Positioning System (GPS)

Since the early 90's GPS satellites have been providing extremely accurate information to the civilian public via commonly available receivers. These GPS receiver units are now available at most large department stores and have been mostly used for aviation, fishing, and hunting. However, due to the extreme accuracy they can provide (down to several Figure 26. Typical supplies used to collect meters), they are quite useful for many mosquito mosquito larvae.control applications. They are already providing useful information on arbovirus surveillance as well as both adult and larval surveillance. In any good surveillance program, especially where large habitats

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Figure 30. Hourly trap

Figure 32. Gravid trap

Figure 31. Omni-Directional Faye-Prince trap

Figure 27. Aspiration Figure 28. CDC trap Figure 29. New Jersey light trap

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