Modulation of odour-guided behaviour in mosquitoes

Abstract

Mosquitoes are emerging as model systems with which to study innate behaviours through neuroethology and functional genomics. Decades of work on these disease vectors have provided a solid behavioural framework describing the distinct repertoire of predominantly odour-mediated behaviours of female mosquitoes, and their dependence on life stage (intrinsic factors) and environmental cues (extrinsic factors). The purpose of this review is to provide an overview of how intrinsic factors, including adult maturation, age, nutritional status, and infection, affect the attraction to plants and feeding on plant fluids, host seeking, blood feeding, supplemental feeding behaviours, pre-oviposition behaviour, and oviposition in female mosquitoes. With the technological advancements in the recent two decades, we have gained a better understanding of which volatile organic compounds are used by mosquitoes to recognise and discriminate among various fitness-enhancing resources, and characterised their neural and molecular correlates. In this review, we present the state of the art of the peripheral olfactory system as described by the neural physiology, functional genomics, and genetics underlying the demonstrated changes in the behavioural repertoire in female mosquitoes. The review is meant as a summary introduction to the current conceptual thinking in the field.

Mosquito Host-Seeking Diel Rhythm and Chemosensory Gene Expression is Affected by Age and Plasmodium Stages

“…To assess the diurnal effect on the locomotor activity of mosquitoes with P. falciparum infection and their respective controls, a mixed model analysis was used (lmer model: constrained by two main explanatory variables, infection status and period of time, as well as the random effect of replication, Supplementary Table 1-2). In the absence of human odour, the diurnal locomotor activity pro le of uninfected mosquitoes con rmed the high activity at dawn (ZT [23][24], with the younger cohort being more active during scotophase with a peak at dawn, whereas the older control females displayed an increased activity at dusk that was maintained until dawn (ZT 0-11: χ The time-of-day, and the stage of P. falciparum sporogony, differentially affected the locomotor activity of the vector (Fig. 1d).…”

“…Mosquito locomotor activity varies temporally in response to host odour and P. falciparum infection Diurnal cycles in An. gambiae locomotor and host-seeking activities were evident, with distinct crepuscular activity peaks culminating in the highest activity at the onset of photophase (ZT [23][24], and low to moderate activity during scotophase (ZT 12-23) and low activity during photophase (ZT 0-11) 26 .…”

“…In depth analysis of the molecular basis of olfaction in mosquitoes, has allowed for the identi cation and functional characterisation of chemosensory gene families, including odorant receptors (Ors), gustatory receptors (Grs), ionotropic receptors (Irs), odorant binding proteins (Obps) and chemosensory proteins (Csps) [15][16][17][18][19] . The expression of select members of these gene families in olfactory-related tissues change in response to adult maturation, age and physiological state [20][21][22][23][24][25] , including infection status 5 . These state-dependent changes in gene abundance coincide with concerted alterations in the sensitivity of olfactory sensory neurones and the behaviour of the mosquitoes 20,21,25 .…”

Variability in human attractiveness to mosquitoes

“…The odor-guided behavior of mosquitoes is determined by intrinsic factors of mosquitoes and extrinsic components from the environment ( Hill & Ignell, 2021 ). Focusing on mosquito-human interactions, the behavior of blood-feeding mosquitoes depends on anthropophily (predilection to feed on humans), endophagy (preference for biting inside houses), and endophily (indoor resting behavior after a blood meal) ( Campos et al, 2019 ).…”

Editorial for the special issue "Olfactory Coding and Circuitries"

“…Also odor detection in mosquitoes is strongly modulated by life stage and internal state. Hill and Ignell (2021) comprehensively review the current knowledge of the mosquito olfactory system with the focus on the plasticity of mosquito behavior and its physiological and molecular bases. The last review of the invertebrate section by Siju et al (2021) describes modulation in Drosophila, by focusing on the role of the neuromodulator dopamine in olfactory processing and behavior.…”