The New Jersey Light Trap: An Old Standard for Most Mosquito Control Programs

Reproduced from the Proceedings of NJMCA. Please use the following citation when referring to this article:

Reinert, W. 1989. The New Jersey Light Trap: An Old Standard for Most Mosquito Control Programs . Proceedings of the Seventy-Sixth Annual Meeting of the New Jersey Mosquito Control Association, Inc. 1989, pp 17-25.

WILLIAM C. REINERT

Atlantic County Mosquito Unit, Division of Parks and Recreation, P.O. Box 719, Northfield, NJ 08225

Abstract:

The New Jersey Light Trap is an important supplement for adult mosquito surveillance but because of differences that occur in the behavior of individual species it is important to recognize that there are factors that influence the reliability of the light trap for adult mosquito surveillance. This paper discusses the use of the New Jersey Light Trap and sets forth guidelines for its use to minimize variation in light trap data for mosquito management.

Introduction:

To perform and evaluate an effective mosquito control program in any area, it is critical to know the abundance and species composition of mosquitoes in that area. The New Jersey Light Trap is one of the most commonly used tools for obtaining this information.

The New Jersey Light Trap has been used by Mosquito Control Agencies, Rutgers University and the New Jersey Department of Health since 1934, as a device for obtaining information for mosquito research and for planning the operation of mosquito control activities. The trap is a simple and practical tool for obtaining data on adult mosquito populations without the variability and costs associated with human collectors.

History of the New Jersey Light Trap:

The first light trap was developed in 1927 at the New Jersey Agricultural Experiment Station and was called the "Sugar Can Trap" because of the container that was used in the design. Mulhern (1932) reported that the trap was capable of collecting as many mosquitoes between dusk and dawn as a human could in a fifteen-minute period. The original trap did not use a fan but the "Air Blast Trap" that was developed in 1930 included a light and fan mounted in a horizontal tube that rotated in response to wind. In the latter part of 1932, the trap was redesigned to be mounted vertically and was designated as the "Model 50 Light Trap". This trap became the standard light trap used in New Jersey and later became known as the "New Jersey Light Trap".

Description of the New Jersey Light Trap:

One of the major points in favor of the New Jersey Light Trap is its simplicity and ease of operation. The trap (Fig. 1), consists of a vertical metal cylinder (a) that is 9 inches in diameter with a 16 inch diameter conical roof (b) that is fitted above the top of the cylinder.

At the apex of the underside of the roof, a socket (c) is provided for a 25 watt light bulb which attracts the mosquitoes to the trap. The entrance to the cylinder is covered with a 1/4 or 5/16 inch mesh screen, (d) to exclude larger insects such as moths and beetles. Within the cylinder, an 8 inch diameter fan (e), run by an electric motor, sucks in mosquitoes that fly to the light. Below the fan is a fine mesh funnel (f) which leads to the collection jar (g). A killing agent (h), such as a piece of vapona strip which is most commonly used today, is placed within the collection jar. A ventilated paper or plastic cup (i) (Rupp, 1984) is placed within the collection jar to separate the insects from the killing agent. The traps are normally run on household current, although they can be modified to run on battery. In most cases, the trap is turned on by an electric eye or timer just before dusk and turned off shortly after dawn.

Uses of the New Jersey Light Trap:

There are two primary functions which the New Jersey Light Trap performs in mosquito surveillance programs. One is to provide a historical record of mosquito abundance and species presence in an area. Historical data show fluctuations on a year to year basis as well as fluctuations over the span of one season. This type of information can be used to document the impact of mosquito control activities and provide the justification for additional control efforts in an area. Light trap records are especially useful for program budgeting and acquiring water management and pesticide use permits.

The second function of the New Jersey Light Trap in county mosquito surveillance programs is to provide rapid information on mosquito abundance and species composition for planning and directing day-today mosquito control activities. In this function, the data acquired by the New Jersey Light Trap are used to 1) determine or to help the need, the timing, and/or the location of pesticide applications, and to monitor the results of those pesticide applications, 2) to help determine the cause of repeated mosquito complaints in a given area, and 3) as a supplement or backup to more expedient surveillance techniques such as landing or bite counts.

Factors Influencing Light Trap Reliability and Variability:

The New Jersey Light Trap can be an effective tool for managing mosquito populations but mosquito species vary in their response to artificial light, climatic conditions, and other natural stimuli. As a result, a great deal of variability is possible in the attraction of mosquitoes to light traps and the accuracy of data resulting from light trap collections.

The two most important sources of variation in light trap collections include nightly variation and variation resulting from trap placement (Huffaker et al., 1932). Nightly variation results in considerable differences in the numbers of mosquitoes captured from night to night due to environmental factors (temperatures relative humidity, lunar cycle) that influence mosquito behavior. Moonlight affects both the efficiency of the light trap and the behavior of the mosquitoes that are being sampled. The brightness of the moon affects the contrast of the trap's light source in relation to the background light that the insect is navigating in (Barr et al., 1960) which in turn affects the attractiveness of the trap to the mosquito. Although it is generally accepted that fewer mosquitoes are caught at full moon than with a new moon, some species' flight activity increases substantially on bright versus moonless nights.

Compounding the variability resulting from moonlight, the effects of temperature and humidity on mosquito activity and light trap collections are well documented. There are varying ranges of temperature and humidity at which individual species are most active. For example, Aedes vexans activity intensifies as the relative humidity increases to 70%. With higher relative humidity, this mosquito shows a decline in activity (Service 1976). It is also generally accepted that Aedes sollicitans activity decreases substantially when temperatures drop below 60°F. It follows that the amount of variability of humidity, temperature, and moonlight throughout the night will affect the numbers of mosquitoes collected in a trap from night to night.

Placement variations refers to the variability of light trap collection due to the location of the trap. The variability factors of location include proximity to a mosquito source, preferred activity and resting area degree of protection from wind and the proximity to artificial background light. Studies have shown that light trap collections can vary significantly with only a 2 to 3 meter change in location (Barr et al 1963).

The actual distance that a mosquito becomes attracted to a light source is unknown but it is thought to be very short and probably varies by species (Service 1976). The affect of background light on light traps is similar to that of moonlight in that it alters the contrast of the trap light as the attraction stimulus. Each of these factors shows that location of the light trap has considerable influence on trap data when comparing species composition, trap to trap collections, and year to year comparisons of individual traps.

Factors Affecting Variability in Light Trap Collections:

We in New Jersey are fortunate that New Jersey Light Traps have been in use in our State since their introduction to mosquito control. We have a good deal of experience in their use and because so many have been placed in the same locations year after year, we have a wealth of historical information.

Table 1 shows that not all mosquito species are attracted to or collected by New Jersey light traps. There is considerable variation in the relative attractiveness of different mosquito species to light. Generally, light traps do not reflect the abundance or presence of species that are negatively phototaxic or only active during the day. In addition, mosquito species that inhabit wooded areas are less attracted to light traps then those which prefer open areas.

TABLE 1. Mosquito species which can and cannot be accurately monitored by the New Jersey Light Trap.

Species Which Can be Accurately Monitored:

Ae. solicitans
Ae. vexans
Ae. cantator
Ae. taeniorhynchus
Ae. trivittatus
Cx. pipiens
Cx. salinarius
An. bradleyi
Cq. perturbans
Ps. columbiae

Species Which Cannot be Accurately Monitored:

Ae. canadensis
Ae. stimulans
Ae. triseriatus
Ae. excrucians
Ae. albopictus
Cx. restuans
Cx. territans
An. punctipennis
An. quadrimaculatus
Cs. melanura
Ps. ferox
Ps. call

Although many different types of light bulbs have been tried in the New Jersey light trap, the clear 25 watt bulb is most widely used. For consistency and historic accuracy, this should continue to be the bulb of choice.

Whenever possible, light traps should be placed in the same location year after year for general surveillance practices. For greater accuracy in measuring population changes, newly installed traps should be located where mosquito populations are high. When installing the trap, be mindful of exterior lighting such as spot lights, windows and exhaust vents. The trap should be placed in an open area, away from buildings, but close to trees and shrubs. Attempts should also be made to protect the traps from prevailing winds. Light traps should be installed so that the bottom of the roof is 5 1/2 feet above the ground.

Although no significant variation has been shown between trap color and species attractiveness, some variability has been suggested for Culex tarsalis (Barr et al., 1963) and variation may exist for other species. Mulhern (1942) suggested that light traps be painted green to blend with their surroundings and most county mosquito control agencies have adopted that recommendation. More important to the exterior trap color is the color of the underside of the roof, which is most commonly painted white. Changing this color will affect light intensity emitted by the trap (Barr et al., 1960) and increase variability in sampling.

The recommended dates for operating the New Jersey light traps are from May 1st through the month of October. Early May collections need not be made as frequently as those during the remainder of the season. May collections, however, may be useful in showing the presence of early season mosquitoes which would otherwise go undetected. Climatic conditions vary considerably year to year in September and October, but trap collections at these times may prevent unwanted surprises during warm spells. Generally, light traps used in New Jersey are operated 7 nights per week, but if light trap data are only used at comparing year to year fluctuations, operating the end of the year for the traps four nights per week will provide accurate information. During the active mosquito season, light trap collections should be identified a minimum of three times per week to supply as up to date information as possible. If light traps are an agency's sole source of adult surveillance, or if they are used to determine pesticide applications, more frequent collections may be necessary.

The most critical element in using light traps to guide day to day operations is the speed and accuracy of mosquito identification. For this information to be most useful, the specimens should, be identified within 24 hrs of collection. When trap collections are exceptionally high, the entire sample need not be identified. It is considered accurate to spread the collection on a grid and subsample 1/4 of the collection as long as at least 100 mosquitoes are identified. Obviously accuracy in identification is critical to help determine the source of the mosquitoes and an appropriate control strategy.

Be aware that the males in the collection may give you useful information. Some counties routinely identify and count the male mosquitoes. In some species, males can be a reliable indicator for the later emergence of females. When using data on male mosquitoes keep in mind that the factors which create variability in female mosquito behavior quite often influence males of the same species differently.

Some agencies use timers and others use electric eyes to operate their light traps. While there has been no significant difference shown on their effect on light trap collections, traps will run at different times depending on which device is used. For consistency, it is suggested that agencies use either all timers or all electric eyes. To assure consistency traps should be calibrated at least every other year.

Management of Light Trap Data: Data collected from New Jersey Light Traps can be analyzed in a variety of ways for use by the mosquito control agency in their operations and for providing information to people outside of mosquito control. The involvement of computers in mosquito control programs dramatically increases the speed at which these data can be processed and with the use of computer graphics the data can be prepared for presentation. Some counties have been successful in adapting Lotus 123 for light trap data processing and others are writing their own programs for this purpose. The computer is especially helpful for subjecting light trap data to the Williams Mean analysis (Table 2), which reduces the influence of a few very high traps on the average of all traps in the series (Downing, 1976).

The following two fairly simple forms of light trap data manipulation which do not require a computer are suggested: a.). Because of the widely fluctuating climatic conditions in May, September, and October it is more accurate to exclude those months when comparing year to year light trap data. b). One of the most effective ways to reduce or correct for nightly variation is to use the five point moving mean as shown in Table 2 (Downing 1976).

TABLE 2. Useful formulas for analyzing mosquito light trap data.

Formula for Williams Mean:

[EXP ({LOG (tl + 1) + LOG (t2 + 1)...}/n)]-l

Where: t = each trap collection

n = number of traps

Formula for Five Point Moving Mean:

1st point = (day 1 + day 2 + day 3 + day 4 + day 5)/5

2nd point = (day 2 + day 3 + day 4 + day 5 + day 6)/5

3rd point = (day 3 + day 4 + day 5 + day 6 + day 7)/5 etc ...

Guidelines for Using the New Jersey Light Trap:

The following guidelines are presented to improve the reliability of light trap usage in county mosquito surveillance programs and encourage uniformity of light trap data throughout the state.

Do not rely on the New Jersey light trap as a reliable indicator for all species. Be aware that there is considerable variation in the relative attractiveness of different mosquitoes to light and evaluate your light trap data accordingly.
Use a clear 25 watt bulb in the trap to make your data comparable with that of other mosquito control agencies.
Whenever possible, place the light traps in the same location year after year.
Be mindful of exterior lighting when installing a light trap an try to place the trap in open areas, away from buildings at height of 5 1/2 ft above the ground.
Paint the exterior of the trap green and the underside of the roof white.
Begin trapping May 1 of each year and continue the trapping program through the month of October. Operate the traps nights per week unless the information is only to be used to compare year to year fluctuations.
Whenever possible, identify the collections within 24 hours.
Be aware that the males in the collection may give use information. A large number of male mosquitoes is an indication that a brood of females is about to emerge in that area.
For consistency, use either all timers or all electric eyes in the traps that make up your surveillance program.
Develop a system to manage your light trap data. Use the "Williams Mean" to adjust for variations between traps an the "5 Point Moving Mean" to correct for nightly variation.

Conclusions:

The New Jersey Light Trap has been and will continue to play a important role in mosquito control in New Jersey. Consistency of operation is the key to the reliability of New Jersey Light Trap use. When used consistently, New Jersey Light Traps are effective for monitoring population changes of some species, but because of species variability and the bias of trap location, the New Jersey Light Trap is general not accurate for comparison of abundance between different mosquito species.

Acknowledgments:

The author would like to thank the Surveillance Symposium Committee members and Dr. Wayne J. Crans for their input on the topic.

References Cited:

Barr, A.R., T.A. Smith, and M.M. Boreham. 1960. Light intensity and the attraction of mosquitoes to light traps. J. Econ. Entomol. 53:876-880.
Barr, A.R., T.A. Smith, M.M. Boreham, and K.E. White. 1963. Evaluation of some factors affecting the efficiency of light traps in collecting mosquito. J. Econ. Entomol. 56:123-127.
Downing, J.D. 1976. Statistical analysis and interpretation of mosquito light trap data. Proc. N.J. Mosq. Control Assoc. 63:127-133.
Huffaker, C.B., and R.C. Black. 1943. A study of methods of sampling adult mosquito populations. J. Econ. Entomol. 36:561-569.
Mulhern, T.D. 1934. A new development in mosquito traps. Proc. N.J. Mosq. Exterm. Assoc. 20:137.
Mulhern, T.D. 1942. New Jersey mechanical trap for mosquito surveys. Circular 421. New Jersey Agricultural Experiment Station, Rutgers University, New Brunswick, NJ. 8pp.
Rupp, H.R. 1984. A plastic cup for use in the New Jersey light trap. Proc. N.J. Mosq. Control Assoc. 70:17.
Service, M.W. 1976. Mosquito Ecology, Field Sampling Methods. Halsted Press. 324-342.

Discussion Followint the Presentation

QUESTION: Does the location of a nearby farm and domestic animals possibly increase the trap collections?

REINERT: I saw some literature that suggests that concentrations of animals serve as an attractant to the mosquitoes and do increase trap collections.

QUESTION: Do you believe that it is enough of a factor to take into consideration when you are setting a trap?

REINERT: Yes I do.