Synergism between ammonia, lactic acid and carboxylic acids as kairomones in the host-seeking behaviour of the malaria mosquito Anopheles gambiae sensu stricto (Diptera: Culicidae)

Abstract

Host odours play a major role in the orientation and host location of blood-feeding mosquitoes. Anopheles gambiae Giles sensu stricto, which is the most important malaria vector in Africa, is a highly anthropophilic mosquito species, and the host-seeking behaviour of the females of this mosquito is guided by volatiles of human origin. Ammonia, lactic acid and several carboxylic acids are known to be present in the human odour blend. We investigated the effect of these compounds on naive female mosquitoes using a dual-port olfactometer. Ammonia was an attractant on its own, whereas lactic acid was not attractive. Carboxylic acids, offered as a mixture of 12 compounds, were repellent at the concentration tested. The addition of ammonia to the carboxylic acid mixture overruled the repellent effect of the latter. Combining ammonia with either lactic acid or the carboxylic acids did not enhance the attractiveness of ammonia alone. However, a synergistic effect was found when ammonia, lactic acid and the carboxylic acids were applied as a blend. Our findings indicate that An. gambiae s.s. relies on the combination of ammonia, lactic acid and carboxylic acids in its orientation to human hosts. The role of lactic acid in this tripartite synergism differs from that reported for the yellow fever mosquito Aedes aegypti.

Olfactory responses in a gustatory organ of the malaria vector mosquito Anopheles gambiae

“…Indeed, all of the acidic stimuli identified in this study have been shown to be present in human sweat͞skin emanations and, in many cases, have been directly linked to behavioral responses in A. gambiae (15, 29 -32). The same is true for ammonia, which works synergistically with other odorants to attract A. gambiae (19).…”

“…In contrast, S1 sensillum neurons showed no response to isovaleric acid, which evokes strong ELG responses ( Fig. 1) as well as 1-octen-3-ol, 2-methyl phenol, 4-methyl phenol, indole, geranyl acetone, and ammonia, which have been identified as human sweat compounds and shown to elicit significant responses from A. gambiae antennal preparations (14,15,(19)(20)(21), (Fig. 1D).…”

Complementary Function and Integrated Wiring of the Evolutionarily DistinctDrosophilaOlfactory Subsystems

“…Mosquito antennae bear sensilla tuned to acids and amines (Qiu et al, 2006), and we suggest that these house neurons expressing mosquito IR orthologs (Croset et al, 2010;Liu et al, 2010). Although carboxylic acids and amines are critical for mammalian host-seeking behavior in mosquitoes (Smallegange et al, 2005), their ecological significance in Drosophila is less clear. Acids and amines may, for example, signal over-fermentation (Ai et al, 2010) or sources of proteins, respectively, in the food substrates of these flies.…”

Effectiveness of Synthetic Versus Natural Human Volatiles as Attractants for <I>Anopheles gambiae</I> (Diptera: Culicidae) Sensu Stricto

“…gambiae (Braks and Takken 1999, Healy and Copland 2000, Qiu et al 2004a, 2006b, Njiru et al 2006) and several VOCs that are present in human sweat and/or in human skin emanations such as short-chain carboxylic acids, ammonia, and L-lactic acid, were found to be attractive to An. gambiae either individually or as blends (Knols et al 1997, Braks et al 2001, Smallegange et al 2005, Njiru et al 2006. These compounds are also attractive to Aedes aegypti L., a mosquito species that is equally anthropophilic and may therefore respond to similar VOCs , Bosch et al 2000, Williams et al 2006.…”

“…In particular, we examined the attractiveness of ammonia that plays a key role as kairomone for An. gambiae (Smallegange et al 2005) and Ae. aegypti , Bosch et al 2000, Williams et al 2006) in relation to the attractiveness of natural human odors.…”