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A Novel in vitro Bioassay to Explore the Repellent Effects of Compounds Against Mosquito (Diptera: Culicidae)

Rehman, Junaid U., Tabanca, Nurhayat, Khan, Ikhlas A.
Journal of medical entomology 2016 v.53 no.1 pp. 157-165
Culicidae, bioassays, cages, carvacrol, collagen, deet, ethanol, females, heat, humans, in vitro studies, insect repellents, insect vectors, mosquito bites, mosquito control, polymethylmethacrylate, reproducibility, risk, thymol
Mosquitoes are vectors for many pathogens that can cause human diseases which can result in high rates of human morbidity and mortality at significant levels of transmission. Repellents play an important role in reducing mosquito bites and hence the risk of spread of mosquito borne diseases. Currently, human arm based bioassay systems are used to identify repellent/deterrent properties of compounds, extracts and essential oils. Risks involved with human arm based (in vivo) systems are allergic reactions and variation in data. These systems require large quantity of test materials which limits the number of replications. We are reporting an in vitro bioassay method "National Center for Natural Product Research (NCNPR) repellent bioassay" that can closely simulate cloth patch bioassay system used to determine repellency against mosquitoes. The NCNPR repellent bioassay uses heat as a stimulus to attract mosquito and edible collagen sheet as alternate to human skin. This system consists of a heating base plate of cup warmer fixed to Plexiglas sheet having a rectangular liquid reservoir of 3 x 4 em used for feeding solution. This base plate containing the feeding solution covered with treated collagen sheet is introduced in 12 x 12 x 12 inches cage containing approximately 200 starved female mosquitoes. Treatments prepared in EtOH were applied in concentrations ranging between 1.5 to 0.011 mg/cm2 in a volume of 50 jJl/20 cm2 area of collagen sheet. Number of mosquito commencing to bite was recorded visually. The minimum effective dose (MED's) (mg/cm2) of compounds: DEET (0.021), carvacrol (0.011), thymol (0.013), undecanoic acid (0.023), thymol methyl ether (0.269) and 2-nonanone (>0.375 mg/cm2)determined in this in vitro system were similar to cloth path bioassay system. This NCNPR repellent bioassay can be used to screen compounds at a faster rate than the cloth patch bioassay, which involves the use of human subjects, with reasonable reproducibility of the data.