Insect Repellents: Effect of Mosquito and Repellent-related Factors on Protection Time12

Use of a semi-field system to evaluate the efficacy of topical repellents under user conditions provides a disease exposure free technique comparable with field data

“…Therefore, experiments carried out in the laboratory may not accurately estimate the efficacy of repellents in the field [4]. Environmental factors such as temperature, humidity and wind speed, all of which affect the effectiveness of repellents, are controlled in the laboratory, but in the field these factors may fluctuate and affect repellent efficacy [5]. As a result, tests carried out in the laboratory ideally should be verified using representative field tests.…”

Mosquito density, biting rate and cage size effects on repellent tests

“…Physical loss of repellent occurs by evaporation, from abrasion (contact with clothing), by washing or rinsing of treated surfaces and due to perspiration (Travis, 1950;Gabel et al, 1976;Rutledge et al, 1985). Light, temperature, humidity and air quality are important environmental factors (Lewis, 1933;Christopher, 1947;Travis, 1950;Shambaugh et al, 1957;Wood, 1968;Lomax & Granett, 1971), as are repellent dose and exposure time, test cage shape and size and the type of test arena that is used (Granett, 1940(Granett, , 1944Bar-Zeev & Smith, 1959;Bar-Zeev & Ben-Tamar, 1971;Lomax & Granett, 1971;Khan et al, 1975;Gabel et al, 1976;Rutledge et al, 1976;Schreck, 1977;Hill et al, 1979;Francis et al, 1993;Rutledge et al, 1994). Biological factors affecting repellent bioassays include larval nutrition, carbohydrate intake by adult mosquitoes, age and parousness of female mosquitoes, and innate differences among repellent-treated test subjects.…”

“…Biological factors affecting repellent bioassays include larval nutrition, carbohydrate intake by adult mosquitoes, age and parousness of female mosquitoes, and innate differences among repellent-treated test subjects. Behavioural factors such as the diel timing and intensity of mosquito biting activity are also important (Khan et al, 1975; Aedes aegypti Large 4.5 Ϯ 0 5.0 Ϯ 0.8 5.5 Ϯ 0.8 Medium 5.5 Ϯ 0.8 6.5 Ϯ 0.8 6.5 Ϯ 0.8 Small 6.0 Ϯ 0 6.0 Ϯ 0 6.5 Ϯ 1.7…”

“…Anopheles quadrimaculatus Large 1.5 Ϯ 0 2.0 Ϯ 0.8 3.0 Ϯ 1.5 Medium 4.5 Ϯ 1.5 6.0 Ϯ 2.6 8.0 Ϯ 3.1 Small 1.5 Ϯ 0 3.2 Ϯ 0.3 6.5 Ϯ 1.7 Xue & Barnard, 1996). Ignorance of temporal blood-feeding patterns can compromise estimates of protection time for repellents that have extended activity (Gouck & Smith, 1962;Smith et al, 1963;Xue & Barnard, 1996), whereas repellent protection time appears to be inversely related to the biting rate (Bacot & Talbot, 1919;Granett, 1940;Khan et al, 1975).…”

“…Results of much research on repellent testing procedures suggest relationships between protection time, the size of the mosquito test population and the mosquito biting rate. Investigations of many test cage configurations and mosquito population sizes (Bar-Zeev & Smith, 1959;Lomax & Granett, 1971;Khan et al, 1975;Schreck, 1977;ASTM, 1983;Francis et al, 1993) have not led to a consensus on the optimal mosquito biting rate and density for repellency tests. Therefore, we sought answers to four basic questions concerning repellent bioassays: (1) does the size of the test cage or the volume of cage space per female mosquito influence the mean duration of protection from mosquito bite (MDPB); (2) do volume and cage size factors influence mosquito biting rates; (3) are MDPB and biting rate responses to cage size and mosquito density comparable for different species, e.g.…”