Male swarming aggregation pheromones increase female attraction and mating success among multiple African malaria vector mosquito species

Abstract

Accumulating behavioural data indicate that aggregation pheromones may mediate formation and sustaining of swarms of mosquitoes. However, chemical cues possibly luring mosquitoes to swarms have not been adequately investigated and the likely molecular incitants of these complex reproductive behaviours remain unknown. Here we show that males of important malaria vector species Anopheles arabiensis and Anopheles gambiae produce and release aggregation pheromones that attract individuals to the swarm, and enhance mating success. We found that males of both species released significantly higher amounts of 3-hydroxi-2-butanon (acetoin), 6-methyl-5-hepten-2-one (sulcatone), octanal, nonanal, and decanal during swarming in the laboratory. Males fed with stable isotope-labelled glucose, revealed that these five compounds were produced by them. A blend composed of synthetic analogues to these swarming odours proved highly attractive to virgin males and females of both species under laboratory conditions and significantly increased mating in five African malaria vectors: An. gambiae, Anopheles coluzzii, An. arabiensis, Anopheles merus and Anopheles funestus in semi-field experiments. Our results not only narrow a conspicuous gap in understanding a vital aspect of the chemical ecology of male mosquitoes but also demonstrate fundamental roles of rhythmic and metabolic genes in the physiology and behavioural regulation of these vectors. These identified aggregation pheromones have great potential for exploitation against these highly dangerous insects. Anopheles males, as among many other mosquito species, form mating swarms 1 that vary in size and temporal stability [2][3][4] . Wild Anopheles males swarm during sunset 1,5-7 and are often found near contrasting shade ground features, presumably guided by that visual cue 1,4,5,8 . Factors and mechanisms of swarming initiation in mosquitoes are still debatable 9 . A few studies have shown that initiation of swarming in mosquitoes is governed by the inherent circadian clock 10,11 and fine-tuned by environmental conditions [12][13][14] . However, very little is known about chemical cues that may mediate the formation and maintenance of male swarms and attracting females to those swarms in order to copulate 15 .2,6,6-trimethylcyclohex-2-ene-1,4-dione was isolated from males and females of Aedes aegypti mosquitoes and stimulated swarming behaviour by increasing number of swarming males and extending activity in a dose depending manner 15 .Another study revealed that under laboratory conditions, swarming of Ae. aegypti males was triggered with a host odour at the onset of scotophase but chemical cues remain unknown 16 .Behavioural tests showed that volatiles released from alive or dead males of three Culex species attracted significantly more conspecific females than the control odour without males 17 pointing out that attraction of females to swarms may be mediated by a sex pheromone. 1-(4-Ethylphenyl) ethanone, produced by both sexes of Ae. aegypti mosquitoes, elicited attraction ...

Mosquito sound communication: are male swarms loud enough to attract females?

“…It is possible that long-range cues are not necessary for the female to arrive at a swarm site. In that case, females may use the close-range sound of a chasing male to avoid being inseminated by the wrong species [ 4 ]; however, investigations on long-range cues such as vision [ 28 ] or olfaction [ 39 , 40 ] should be pursued in future research.…”

The Expression of Chemosensory Genes in Male Maxillary Palps ofAnopheles coluzzii(Diptera: Culicidae) andAn. quadriannulatus

“…A blend of these pheromones attracts males and females from a range of Anopheles species, including An. coluzzii ( Mozūraitis et al 2020 ). An.…”

“…Females use odor cues to detect vertebrate hosts, sugar sources, and oviposition sites ( Clements 1999 ). The role of olfaction in male anophelines is less well understood, although recent work by Mozüraitis et al (2020) demonstrated that male An. gambiae Say and An.…”

Mosquito sound communication: are male swarms loud enough to attract females?

“…It is possible that long-range cues are not necessary for the female to arrive at a swarm site. In that case, females may use the close-range sound of a chasing male to avoid being inseminated by the wrong species (4) , however, investigations on long-range cues such as vision (29) or olfaction (39, 40 ) should be pursued in future research.…”