Biogents – Science for Your Protection –

WHO-Cone test / WHO-Tube test

WHO-Cone test

WHO-cone tests were originally designed to evaluate the toxicity of insecticide-treated bednets against malaria mosquitoes. They are also suited to investigate the toxicity of other impregnated (textile) surfaces. Our test procedure follows the WHO regulations (WHO, 1998: Test Procedures for Insecticide Resistance Monitoring in Malaria Vectors, Bio-Efficacy and Persistence of Insecticides on Treated Surfaces).

Procedure

Standard WHO plastic cones are attached to the treated test surface. Afterwards, five female mosquitoes are transferred into one cone with an aspirator, and exposed to the treated surface for three minutes. At the end of the exposure, test mosquitoes are removed from the cones, placed in small cages for further observation, and kept in insecticide-free air. The number of immobilized (knocked-down) test mosquitoes is documented one hour after the exposition, and the mortality rate (=knock-dead) is determined after 24 hours. Each textile/test surface is tested in ten repetitions on a total of 50 test mosquitoes. In addition, the natural mortality rate is determined with an untreated textile on another 50 test mosquitoes.

Problems

Some insecticides that belong to the group of pyrethroids (e.g., permethrin) show certain excito-repellent effects on the test mosquitoes. Mosquitoes are able to perceive the intoxication after the exposure to permethrin, and try to escape from the treated surface. As a consequence, an increased flying behavior inside the cones can be observed, and exposure is reduced. Textiles that are treated with permethrin should be evaluated in standard WHO tubes as their inner walls are completely covered, and mosquitoes are constantly forced to contact the treated surface. The WHO recommends an exposure time of three minutes for the evaluation of treated bednets. This time span might be too short for testing impregnated apparel, which is usually treated with other active ingredients and concentrations. The WHO gives no recommendations for the evaluation of these group of textiles.Thus, Biogents defines the exposure time after consultation with our customers. WHO-Cone tests can be performed with all mosquito species from our insectary.

WHO-Tube test

The original purpose of the WHO-Tube test is to verify the susceptibility of wild mosquito populations to certain insecticides. This enables a quick reaction in case of fulminating resistent individuals by changing pest control strategies (WHO-Susceptibility-Bioassay, 1981). The WHO also recommends the use of tubes as an alternative to WHO cones for the toxicity evaluation of treated surfaces. A technical delivery specification of the German Armed Forces also demands the use of tubes to test the bioactivity of textiles with vector protection.

Procedure

The test material is attached to the inner wall of a WHO standard tube. Afterwards, ten female mosquitoes are transferred into the test tube, and exposed to the treated surface for a specific exposure time. At the end of the test, mosquitoes are removed from the test tube, placed in small cages for further observation, and kept in insecticide-free air. The number of immobilized, knocked-down test mosquitoes is documented one hour after the exposition. The mortality rate (=knock-dead) is determined after 24 hours. Each textile is tested in five repetitions on a total of 50 test mosquitoes. In addition, the natural mortality rate is determined with an untreated textile on another 50 test mosquitoes.

Problems

The WHO recommends an exposition time of three minutes for the evaluation of treated bednets. This time span might be too short for testing impregnated apparel, which is usually treated with other active ingredients and concentrations. The WHO gives no recommendations for the evaluation of these group of textiles. Thus, Biogents defines the exposition time after consultation with our customers. WHO tube tests can be performed with all mosquito species from our insectary.