Medical and Veterinary Entomology (2006) 20, 280–287 doi: 10.1111/j.1365-2915.2006.00627.x © 2006 The Authors 280 Journal compilation © 2006 The Royal Entomological Society Introduction Most female mosquitoes require blood meals for reproduction. Physical and chemical cues emanating from the host guide fe- male mosquitoes to these blood sources. Although optical cues and physical cues such as heat and moisture play a role in host location, chemical cues are considered to be the most important (Takken, 1991). Water vapour, carbon dioxide and ammonia are considered to be important cues for guiding mosquitoes to their human hosts (Price et al., 1979; Braks et al., 2001). In ad- dition, organic chemicals such as a number of carboxylic acids, lactic acid, 1-octen-3-ol and acetone have been shown to attract anthropophilic mosquitoes (Takken et al., 1997; Bosch et al., 2000). It is commonly observed that, when two persons are equally accessible, one person receives more mosquito bites than the other. The mechanisms underlying such discrimination await elucidation. Numerous studies have been published on the dif- ferential attractiveness of human individuals to mosquitoes (Muirhead-Thomson, 1951; Smith, 1956; Brouwer, 1960; Mayer & James, 1969; Carnevale et al., 1978; Curtis et al., 1987; Schreck et al., 1990; Lindsay et al., 1993; Knols et al., 1995; Brady et al., 1997; Mukabana et al., 2004). Smart & Brown (1957) observed a higher landing frequency on hands with a darker colour. These authors also reported that when the highly anthropophilic mosquito Aedes aegypti (L.) is offered hands by two individuals with different temperatures, it alights more often on the warmer hand. Schreck et al. (1990) studied human ema- nations collected on glass Petri dishes and tested their attractive- ness when kept at different temperatures. They demonstrated that although heat is not required to attract mosquitoes, warmed human skin residues attracted higher numbers of Ae. aegypti. Interindividual variation in the attractiveness of human odours to the malaria mosquito Anopheles gambiae s. s. Y. T. QIU 1 , R. C. SMALLEGANGE 1 , J. J. A. VAN LOON 1 , C. J. F. TER BRAAK 2 and W. TAKKEN 1 1 Laboratory of Entomology, Wageningen University, Wageningen, the Netherlands and 2 Biometris, Plant Research International, Wageningen University and Research Centre, Wageningen, the Netherlands Abstract. Differences between human individuals in their attractiveness to female mosquitoes have been reported repeatedly, but the underlying mechanisms are not well understood. Skin emanations from 27 human individuals, collected on glass marbles, were tested against ammonia in a dual-choice olfactometer to establish their degrees of attractiveness to anthropophilic Anopheles gambiae s.s. Giles (Diptera: Culicidae) mos- quitoes. Ammonia was used as a standard odour source because of its proven attractive- ness to An. gambiae s.s. Skin emanations from most volunteers attracted significantly more mosquitoes than ammonia. There were clear differences in the attractiveness of skin emanations from different volunteers relative to that of ammonia, as well as in the strength of the trap entry response. Consistent differences were observed when emana- tions from the three most and the three least attractive volunteers were tested pairwise. No gender or age effect was found for relative attractiveness or trap entry response. Emanations from volunteers with higher behavioural attractiveness elicited higher elec- troantennogram response amplitudes in two pairs, but in a third pair a higher electroan- tennogram response was found for the less attractive volunteer. These results confirm that odour contributes to the differences in attractiveness of humans to mosquitoes. Key words. Anopheles gambiae, electroantennogram, host-seeking behaviour, human odours, malaria mosquito, olfaction. Correspondence: Dr Willem Takken, Laboratory of Entomology, Wageningen University, PO Box 8031, 6700 EH, Wageningen, the Netherlands. e-mail: willem.takken@wur.nl