Isolation and Identification of Behaviourally Active Semiochemicals from Human Foot Odour as Attractants for African Malaria Vectors

Abstract

Despite their small size and short lifetime, mosquitoes (Diptera: Culicidae) are vectors of diseases of vast economic and medical importance. They transmit life threatening human and animal diseases, in addition to their buzzing, biting and annoyance. Questions on why mosquitoes are attracted to certain hosts and what attractants are responsible for their odour mediated behaviour remain unanswered. There is a plethora of evidence suggesting that mosquito host-seeking behaviour is mediated by a wide range of info-chemicals. Mosquito chemical ecology remains poorly understood. With improved knowledge of the role of the chemical cues in mosquito behaviour, new methods of mosquito control based on behaviour-modifying cues could be implemented, thus leading to effective and improved control of the spread of the dangerous pathogens such as, the malaria causing parasites (Plasmodium spp). Various human volatiles (kairomones) have been observed to mediate the hostseeking process in laboratory settings, yet no effective bait has been identified for field application. In this work, 11 Electro-antennogram (EAG) active compounds were identified from the human foot odour. Subtraction bio-assays under laboratory and semi-field conditions of the EAG active compounds revealed that 3 out of the 11 were allomones, while the remaining 8 were important kairomonel blend components of the human foot odour to Anopheles gambiae sensu sitricto mosquitoes. The results show that these compounds are effective as a blend and that the differential attractiveness of the malaria vectors to human feet is due to quantitative differences in the production of these compounds. Anopheles gambiae s.s. and An. funestus have been trapped with human foot odour baited Counter Flow Geometry (CFG) traps under semi-field conditions in western Kenya. Several entomopathogens have been shown to be effective against mosquitoes, but their application is difficult. The use of attractants could improve the efficacy of entomopathogens as means of controlling anopheline mosquito population and hence malaria transmission.