Efficacy Testing of Repellents

Efficacy Testing of Repellents

The efficacy of repellents is of high health importance. Efficacy is influenced by test persons used, insect species, age of insect, temperature, humidity as well as  various other factors. To generate comparable results, test Guidelines were developed for the evaluation of repellents by authorities and WHO.

Guidelines
Different Guidelines are listed in the table below.
Table 1: International test guidelines of personal repellent products

PublisherName of guidelineInternet link
OPPTS, US EPA810.3700 Insect Repellents for Human Skin and Outdoor Premiseshttp://www.epa.gov/ocspp/pubs/frs/home/draftguidelines.htm
WHOWHO/HTM/NTD/WHOPES/2009.4 Guidelines for Efficacy Testing of Mosquito Repellents for Human Skinhttp://whqlibdoc.who.int/hq/2009/WHO_HTM_NTD_WHOPES_2009.4_eng.pdf
EUROPEAN COMISSIONTechnical Notes of Guidence: Insecticides, Acaricides and products to control other arthropods (PT 18) and Repellents and attractans  (only concerning arthropods) (PT 19). Draft guidance document to replace part of Appendices to chapter 7 (page 187 to 200) of the TNsG on Product evaluation.http://ec.europa.eu/environment/biocides/pdf/guidance_efficacy_pt18_19.pdf
SABSSouth African Bureau of Standards: Pesticides – Biological evaluation of the efficacy of mosquito repellents – first revisionwww.sabs.co.za
 

Comparison of Repellent Performance

The test guidelines above are excellent scientific tools to compare repellent products. To compare the performance of different active substances the scientist has to fulfill additional basic rules of science:

  1. The concentration of the tested active substances have to be the same
  2. The formulation matrix of both repellents have to be the same. Ingredients of formulations influence the performance. If you compare results shown in the “mosquito” folder, you can recognize that the efficacy of a lotion with 10% IR3535® has the same efficacy as the 20% IR3535® pump spray.

The performance of repellents vary with insect species tested. 
We collected IR3535® data of tests performed with health relevant species of mosquitoes (Aedes, Culex an Anopheles), and ticks.
download (PDF) – efficacy summary IR3535®

 

Testing with Mosquitoes and Flies

Testing against mosquitoes and flies is performed in the field or in mosquito cages. The arm is inserted for exposure to potential bites. For cage testing, scientists have to reproduce mosquitoes or flies. Very often only females are selected for testing and very high numbers (sometimes 300) are used. Therefore, protection times measured by cage testing sometimes tend to be lower in comparison to field test results. The Guidelines recommend mosquito species which are known to transmit diseases. Species include the Aedes and Culex and Anopheles mosquitoes.
Cage testing is the only method that bears nearly no risk of disease transmission. Field tests, on the other hand, need to be performed with very experienced volunteers. Despite the risk, field tests are of higher scientific value and importance because they reflect the reality of the situation. Tests begin when the scientist proves that mosquito or fly females show a high willingness to bite. Therefore, one or two volunteers are needed to expose non-protected skin (arm or leg). During cage testing, 10 bites in 30 seconds are sometimes measured. This value is called “biting pressure”. The “biting pressure” with non-protected skin and the Complete Protection Time (CPT) with repellent treated skin are determined during testing.  The CPT is the time of hours after which the first mosquito bite occurred once a second bite has been confirmed. Repellent testing is challenging as the exposure to mosquito or fly bites may last 4 to 12 hours for defined intervals. The results are used for label claims like “protection for up to 8 hours” as measured for the IR3535® formulation shown in the “mosquito” folder.
 

Testing with Ticks

Testing with ticks may be less challenging but patience is required. This testing is performed in entomologic laboratories (labs of insect scientists) and the test method may vary. In any case the scientist has to reproduce the ticks under controlled conditions. Some scientists perform testing in the following way: They carefully place test ticks to defined parts of the skin every hour for a few minutes and observe the movement of the tick. The test ticks navigate guided by exhaled carbon dioxide towards the direction of the test person’s head. Therefore, the tick is placed on the hand, arm or leg below a repellent treated skin part. The scientist repeats this test every hour until the tick crosses the repellent treated skin area. The measured time is named Complete Protection Time (CPT).