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 ...

In eco‐evolutionary studies of parasite–host interactions, virulence is defined as a reduction in host fitness as a result of infection relative to an uninfected host. Pathogen virulence may either promote parasite transmission, when correlated with higher parasite replication rate, or decrease the transmission rate if the pathogen quickly kills the host. This evolutionary mechanism, referred to as ‘trade‐off’ theory, proposes that pathogen virulence evolves towards a level that most benefits the transmission. It has been generally predicted that pathogens evolve towards low virulence in their insect vectors, mainly due to the high dependence of parasite transmission on their vector survival. Therefore, the degree of virulence which malaria parasites impose on mosquito vectors may depend on several external and internal factors. Here, we review briefly (i) the role of mosquito in parasite development, with a particular focus on mosquito midgut as the battleground between Plasmodium and the mosquito host. We aim to point out (ii) the histology of the mosquito midgut epithelium and its role in host defence against parasite's countermeasures in the three main battle sites, namely (a) the lumen (microbiota and biochemical environment), (b) the peritrophic membrane (physical barrier) and (c) the tubular epithelium including the basal membrane (physical and biochemical barrier). Lastly, (iii) we describe the impact which malaria parasite and its virulence factors have on mosquito fitness.

Approximately 120 years ago the link between mosquito and the malaria transmission was discovered. However, even today it remains an open question whether the parasite is able to direct the blood-seeking and feeding behavior of its mosquito vector to maximize the probability of transmission. If the parasite has this ability, could it occur only through the alteration of the vertebrate host's volatile organic compounds (VOCs) and/or the parasite alteration of the behavior of the infected vector in a manner that favors its transmission? Although some recent empirical evidence supports the hypothesis regarding the parasite ability in alteration of the vertebrate host's VOCs, the role of parasite alteration and behavioral differences between infected and uninfected female mosquitoes toward infected and uninfected hosts has not yet been considered in the implementation of control measures. This review will discuss the current evidence, which shows 1. Plasmodium can direct uninfected mosquito blood-seeking and feeding behavior via alteration of vertebrate-host odor profiles and production of phagostimulants and 2. Plasmodium also manipulates its vector during the sporogony cycle to increase transmission. Briefly, we also consider the next generation of methods for moving the empirical laboratory evidence to potential application in future integrated malaria control programs.

Recent data show that parasites manipulate the physiology of mosquitoes and human hosts to increase the probability of transmission. Here, we investigate phagostimulant activity of Plasmodium-metabolite, (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP), in the primary vectors of multiple human diseases, Anopheles coluzzii, An. arabiensis, An. gambiae s.s., Aedes aegypti, and Culex pipiens/Culex torrentium complex species. The addition of 10 µM HMBPP to blood meals significantly increased feeding in all the species investigated. Moreover, HMBPP also exhibited a phagostimulant property in plant-based-artificial-feeding-solution made of beetroot juice adjusted to neutral pH similar to that of blood. The addition of AlbuMAXTM as a lipid/protein source significantly improved the feeding rate of An. gambiae s.l. females providing optimised plant-based-artificial-feeding-solution for delivery toxins to control vector populations. Among natural and synthetic toxins tested, only fipronil sulfone did not reduce feeding. Overall, the toxic-plant-based-artificial-feeding-solution showed potential as an effector in environmentally friendly vector-control strategies.

Malaria parasites can affect vector-related behaviours, increasing transmission success. Using Anopheles gambiae and Plasmodium falciparum, we consider the effect of interaction between infection stage and vector age on diel locomotion in response to human odour and the expression of antennal chemosensory genes. We identified age-dependent behavioural diel compartmentalisation by uninfected females post-blood meal. Infection disrupts overall and diel activity patterns compared with age-matched controls. In this study, mosquitoes carrying transmissible sporozoites were more active, shifting activity periods which corresponded with human host availability, in response to human odour. Older, uninfected, blood-fed females displayed reduced activity during their peak host-seeking period in response to human odour. Age- and infection stage-specific changes in odour-mediated locomotion coincide with altered transcript abundance of select chemosensory genes suggesting a possible molecular mechanism regulating the behaviour. We hypothesize that vector-related behaviours of female mosquitoes are altered by infection stage and further modulated by the age post-blood meal of the vector. Findings may have important implications for malaria transmission and disease dynamics.