Mass spectrometric analysis of human skin
emanations to identify compounds that
influence the host-seeking behaviour of
mosquitoes

U. R. Bernier

United States Department of Agriculture-Agricultural Research Service, Center for Medical, Agricultural, and Veterinary Entomology, 1600 SW 23 rd Drive, Gainesville, FL 32608, USA

Kairomones produced by a host, and specifically human hosts, play a major role in the host-seeking behavior of anthropophilic female mosquitoes Because of the disease vectoring capability of mosquitoes that feed upon human hosts, efforts are being made to discover the identity of the chemical compounds that are used in host-location. Multiple sampling techniques for collecting and characterizing human odors have been developed and used to compile a thorough understanding of the volatile chemicals given off by human skin. The sampling techniques mainly comprise collection of chemical emanations in the gas phase with detection by mass spectrometry. One means of allowing for sample identification of highly polar compounds is the use of small glass beads to collect residue from human skin. Although this method does discriminate against highly volatile compounds, it allows for solvent-free loading of the sample and minimizes water deposition from perspiration. Use of this technique has led to the isolation and identification of over 270 compounds present in analyses of human emanations. To adequately characterize the most volatile compounds given off from the skin, purge and trap mass spectrometry was employed to analyze headspace collections of air above a human arm. This technique discriminates against polar compounds, but combined with the glass bead technique, provides a more exact compilation of human produced compounds. Information obtained from these complementary analyses has resulted in the discovery of attractant blends for Aedes aegypti, Anopheles albimanus, and Ae. albopictus. Effective blends do not involve the use of carbon dioxide, except in the case of Ae. albopictus, where a suitable substitute for carbon dioxide has not yet been discovered. The best blends are either as efficient, or more efficient than the human arm at attracting laboratory mosquitoes when tested in a triple cage dual port olfactometer. The blends are comprised of as little as two compounds, but become more effective as the number of attractant compounds is increased. Currently, the best blends comprise three components. These are being tested in the field as a way to enhance the efficiency of surveillance traps. Some human-produced emanations have been found to inhibit the attraction of mosquitoes to blends and to the human arm; the potential for use of these in attraction-antagonist technologies is being explored.

Index terms: Aedes aegypti, Anopheles albimanus, kairomones, attractants, GC/MS

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