Landing Rates and Bite Counts for Nuisance Evaluation

Proceedings of the Seventy-Sixth Annual Meeting of the New Jersey Mosquito Control Association, Inc. 1989, pp 34-37.

(Please use this citation when referring to this work)

RODERIC F. SCHMIDT

Middlesex County Mosquito Extermination Commission, 200 Parsonage Road, Edison, NJ 08820

Abstract:

County mosquito control agencies in New Jersey were polled in their methods of conducting landing rates and bite counts. Using this information and other references, guidelines are presented to create a unified approach in the use of landing rate/bite count data for mosquito control.

Introduction:

In preparation for this talk on landing rates and bites counts, I conducted a survey of New Jersey mosquito control agencies and discovered that there is wide variation on how the counts are conducted. In some cases, the agencies indicated that they made no distinction between the two. This paper will attempt to distinguish the differences and make guidelines for their usage in mosquito control.

The Evolution of Bite Count Methodology

At one point in the history of New Jersey mosquito control there was no formal adult surveillance. Mosquito control agencies thought that by polling the people that lived in an area where reduction work was taking place they could determine how successful the effort was. This type of surveillance proved unreliable so the birth of adult surveillance occurred.

You will have to remember that this took place before the New Jersey light trap existed. Before the light bulb was used as an attractant, the human body was used as the substitute. This type of adult surveillance was not referred to as either a landing or bite count but as a day or night collection. The first recorded information I could find on adult surveillance was written by Dr. Headlee in 1917.

He talked of a day collecting trip to the New Jersey shore for Aedes sollicitans and I quote, "All collections were made in shrubbery or tall weeds in broad daylight. All collections were the work of two (2) collection bottles. When the total catch in five (5) minutes reached 30 the limiting factor became the length of time necessary for the bottles to kill.

For information on night adult surveillance I asked Mr. Jessie B. Leslie if he could help me and he agreed. To the best of Mr. Leslie's recollection, a night collection was twenty (20) minutes in duration. Each inspector was assigned a location, Mr. Leslie's being in Carlstadt on top of a hill. The inspector would report to his post at dusk, roll up his sleeves and wait. They would use killing tubes to capture the insects. As Mr. Leslie told me, "it was primitive but effective and as we were starting from scratch, it did help to give us the necessary information as to density and species". Change the wording a little and these descriptions could be the landing or bite counts taken last summer.

When adult surveillance came into greater use, the shortcomings and variables became apparent. They included: mosquito habits, air movements, atmospheric moisture, temperature, light intensity, precipitation, elevation, plant growth, differences in collectors (such as bodily attractiveness, manual dexterity in catching the mosquitoes and earnestness with which the mosquito employees performed their job of collecting). All of these variables still exist today yet the list comes from a paper given by Dr. Headlee in 1922 at the ninth annual meeting of the New Jersey Mosquito Extermination Association. The New Jersey light trap was invented because of the variables encountered by the early mosquito control workers, but that is another story. In summary, day collections were called landing counts and night collections were termed for bite counts. There might be an evolutionary connection.

Results of the Questionnaire:

Most counties define a landing rate as an observation on the density of mosquitoes in an area with little or no concern for species present. They are concerned with the numbers that are coming to bite rather than the species composition. On the other hand, most counties use a bite count when the agency wants to have hard evidence on the number of mosquitoes coming to feed plus what species they are.

Most mosquito control agencies have an official form on which to record this information. The form has a space to record the start and finish of the count, location at which it was taken, species collected and some types of meteorological observations.

The time at which either landing rates or bite counts are conducted varies among the different agencies. Both methods were conducted during the daytime as well as evening with most of the counties taking them in the evening until slightly after sunset or until artificial light was needed.

When artificial light is necessary, a flashlight is usually used although some agencies make use of vehicle headlights. Two agencies used red filters on their flashlights; most use unfiltered light.

Most agencies use one or two people to make the counts but the team may be as high as four. The special instructions varied considerably and often conflicted from county to county. The following is a list of the instructions we received in the poll:

1. Wait a period of time before starting to collect. The wait varied from 15 seconds to 5 minutes.
2. Disturb the vegetation before starting.
3. Turn around several times before starting.
4. Turn around 180' and face the direction you came from before starting.
5. Roll up sleeves before starting.
6. Roll up pant legs before starting.
7. Wear a long sleeved shirt.
8. Wear a short sleeved shirt.
9. Wear light colored clothes.
10. Wear dark colored clothes.
11. Wear no repellents.
12. Wear no toiletries.
13. Stand up while taking count.
14. Count only mosquitoes landing from the waist down.

There was also variation regarding the duration of the counts. Most agencies take bite counts over a 5-10 min. period and record landing rates for 1 min. Some agencies, however, prefer periods that vary from 1 min. to as high as 30 min. for either technique. When mosquitoes are actually collected, most agencies identify them to species and keep the information on a special form. Many make the information available to the homeowner if the data are collected in the homeowner's yard.

Landing rate and bite count data are used for many different purposes by the mosquito control agencies that were polled. The primary use is justification for adulticiding. Other uses include: 1) Justification for water management projects, 2) Effectiveness of adulticiding, 3) Larval habitat location, 4) Vector potential of biting populations, 5) Light trap placement, 6) Improved larval surveillance and 7) A comparison of biting populations vs. light trap data.

Guidelines for Conducting Bite Counts and Landing Rates:

The more I looked at the information from the questionnaire the only thing of uniformity that came out of it was how non-uniform we are as mosquito control agencies. The following guidelines are presented to eliminate variation when we conduct our landing rates and bite counts.

The term "Landing Rate" should be used when an individual records the number of mosquitoes that land on the observer over a designated period of time. We suggest that they be taken over either a I or 5 min. period. If the landing rates exceed 50 in 30 sec., the interval can be shortened to protect observers that are expected to conduct numerous counts. Landing rates may involve speciation, if desired, but they are normally employed in areas where a single, known species is the sole cause of annoyance.

The term "Bite Count" should be used when an individual captures each mosquito that comes to bite over a designated time interval for species determination. Bite counts are most useful in areas where the biting populations consist of mixed species. The same time restrictions can be employed with an upper limit of ten (10) minutes when the biting populations are extremely low.

The following guidelines apply to both landing rate collections and bite count collections:

1. Wear solid color clothing whenever possible. Mosquitoes are more easily seen on a solid vs. patterned background.
2. Maintain a consistent clothing color among the counters within a county to keep the results comparable. Mosquitoes do exhibit color preferences and wide variation in the background color of the clothing could cause variation within the data set.
3. No repellents, after-shaves or perfumes should be used.
4. Take all landing rate and bite counts from a standing position.
5. Disturb the surrounding vegetation before starting the counts.
6. Count only those mosquitoes that land within view. This permits county agencies to use one person to accomplish the jobs and is based primarily on economics.
7. If work is conducted after sunset, the light source should have a red filter. Red light is less repelling than white light.
8. Develop a standardized form to facilitate the recording and filing of information.
9. Use real numbers on all forms. One hundred plus (100+) tells the foreman or director there are a lot of mosquitoes but for mathematical analysis 100+ is useless. One hundred twenty (120) or two hundred (200) are much more meaningful.
10. When collecting mosquitoes for identification, use some type of aspirator, either electric or lung powered.
11. Be aware of the behavior of the species that is being monitored when interpreting data from landing rates and bite counts. Landing rates taken at mid day for a mosquito species that host-seeks at twilight may require adjustment to assess the magnitude of the problem. The timing of the landing rate or bite count should coincide with the period of greatest activity whenever possible.

References Cited:

• Headlee, T.J. 1921. The Mosquitoes of New Jersey and their Control. N.J. Agricultural Experiment Station Bull. 348, New Brunswick, NJ. 229 pp.
• Headlee, T.J. 1922. The problem of evaluating mosquito density and the advantages to be realized from its solution. Proc. N.J. Mosq. Exterm. Assoc. 9:48-56.
• Leslie, J.B. 1985. Mosquito Control: A Historical View. Proc. N.J. Mosq. Control Assoc., 72:17-21.