The research, published in BMC Environmental Science, was led by Lauren E. Johnson of Washington University in St. Louis together with colleagues at Tyson Research Center. During the summer of 2023, the team enrolled 58 households across the St. Louis metropolitan region, deliberately selecting sites along a wide gradient of artificial sky brightness ranging from roughly 1,020 to 10,500 microcandelas per square meter. At each site, they deployed BG-Sentinel traps programmed to run from 10 p.m. to 4 a.m., capturing host-seeking females and mate-seeking males. The traps mimic a human host by releasing carbon dioxide from dry ice and artificial human skin odors, while their high-contrast black and white design appeals to the visually oriented tiger mosquito. Each morning, the researchers collected, sexed, and identified the catch, and they also sampled mosquitoes with aspirators in the early evening to estimate baseline abundance at every location.

Temperature proved to be a critical piece of the puzzle. Field loggers and National Weather Service records showed that daytime maximum temperatures during the study swung by as much as 13 degrees Celsius, from 25.5 to 38.3 degrees. That upper range matters because laboratory work on St. Louis tiger mosquitoes has pegged their critical thermal maximum—the temperature beyond which survival is threatened—at around 36.7 degrees. In other words, the mosquitoes in this study were frequently confronting conditions hot enough to make daytime activity genuinely dangerous, since a blood meal itself can raise a female’s body temperature to lethal levels.

To untangle the effects of light pollution and heat, the team turned to generalized additive models fitted with negative binomial distributions, an approach well suited to non-linear relationships and overdispersed count data. They also included percent impervious surface cover, a standard proxy for urbanization drawn from the national land cover database, to ensure that any apparent effect of artificial light was not simply a stand-in for dense development. A spatial autocorrelation test using Moran’s I confirmed that neither daytime nor nighttime abundance was clustered geographically, allowing the analysis to proceed without spatial corrections.

The results were striking. The best-fitting model explained 61.9 percent of the variance in nighttime mosquito abundance, and the two dominant predictors were nearly tied: daytime abundance accounted for 28.22 percent of explained variance, while the interaction between artificial light at night and temperature accounted for 28.17 percent. Impervious surface, by contrast, contributed a mere 2.86 percent, suggesting that urbanization per se is a far weaker driver of nocturnal activity than the light and heat conditions themselves. Every term in the model was statistically significant.

The shape of the light response was decidedly non-linear. Nighttime captures were essentially zero at the darkest sites, but abundance climbed sharply once artificial sky brightness crossed roughly 3,500 microcandelas per square meter, remaining elevated all the way to the brightest locations. This threshold pattern mirrors laboratory experiments showing that below a biologically meaningful intensity, artificial light has little effect on tiger mosquito behavior, but once that intensity is reached, nighttime activity switches on dramatically. The authors note that this kind of threshold effect would likely be missed by studies that treat light pollution as a simple presence-or-absence variable, underscoring the value of sampling along a continuous gradient.

Temperature determined whether that threshold mattered. When the researchers colored their data points by whether the preceding day’s maximum temperature had reached or exceeded the females’ critical thermal maximum, a clear pattern emerged: nearly every sampling event following such a scorching day showed some nighttime activity, and the few exceptions occurred almost exclusively at sites below the 3,500-microcandela threshold. Model predictions told the same story. At 40 degrees Celsius, predicted nighttime abundance rose steeply with light pollution; at 35 degrees the increase was gentler; and at or below 30 degrees, the model predicted essentially no night activity regardless of brightness. Dark sites showed little to no nocturnal capture even on the hottest days, indicating that heat alone was not enough—the mosquitoes needed light to exploit the night.

The most likely interpretation is that artificial light unlocks a temporal refuge from thermal stress. Diurnal species that use light as an exogenous cue for navigation and timing may, under light-polluted skies, gain access to a nighttime niche that would otherwise be inaccessible. By shifting host-seeking into cooler, illuminated hours, female tiger mosquitoes can avoid the lethal costs of blood-feeding during heat extremes while still securing the nutrition needed for egg production. Similar heat-driven nocturnality has been documented in other day-active animals, including the white-lipped peccary, but the mosquito study is among the first to demonstrate the phenomenon in a wild disease-vector population and to identify light pollution as the enabling condition.

The findings carry real public health weight. Aedes albopictus is a competent vector of dengue, chikungunya, and Zika viruses and one of the most abundant urban mosquitoes in the temperate United States. If hot weather and bright nights routinely extend its biting window into the hours when people sit on porches, sleep with open windows, or walk lit streets, the geometry of vector-host contact changes. Notably, the effect runs in the opposite direction for nocturnal, light-avoiding Anopheles mosquitoes, in which even brief light exposure suppresses biting for hours. Species-specific responses like these could reshape disease transmission dynamics in densely populated urban areas where both heat waves and light pollution are intensifying, and they argue for control strategies timed to these expanded activity periods rather than the traditional dawn-and-dusk schedule.

The study also bridges a persistent gap between laboratory and field. Controlled experiments had long shown that artificial light at night activates nighttime biting in Aedes aegypti and Aedes albopictus and disrupts clock gene expression, but evidence from wild populations remained thin; the closest precedent was a modeling study in a large Chinese city that reported high nocturnal activity without pinpointing a cause. By sampling 58 sites across a broad brightness gradient and pairing the data with precise temperature records, the St. Louis team confirmed that laboratory observations translate to real urban landscapes. Open questions remain, including whether the nocturnal shift represents a permanent expansion of the species’ activity period or a temporary behavioral adjustment, and how chronic light exposure might interact with seasonal processes such as diapause. What is already clear, however, is that as cities grow hotter and brighter, the tiger mosquito’s day is stretching into the night.

Subject of Research: Effects of artificial light at night and heat on the nocturnal activity of the tiger mosquito Aedes albopictus

Article Title: Hot days and light-polluted nights increase nighttime activity of the diurnal tiger mosquito (Aedes albopictus)

Article References: Johnson, L. E., Tayon, L. L., Uder, E. R., Dobbs, K. G., Radomski, T., Medley, K. A., & Westby, K. M. (2025). Hot days and light-polluted nights increase nighttime activity of the diurnal tiger mosquito (Aedes albopictus). BMC Environmental Science, 2(1), Article 15. https://doi.org/10.1186/s44329-025-00029-3

Image Credits: AI Generated

DOI: 10.1186/s44329-025-00029-3

Keywords: Aedes albopictus, tiger mosquito, light pollution, artificial light at night, heat waves, vector-borne disease, urban ecology, circadian rhythms, host-seeking, climate change, public health, mosquito control

At the heart of the review is the idea that host seeking unfolds through overlapping phases: activation, orientation, approach, landing, probing, and feeding. Each phase depends on different cues with different reliability. Carbon dioxide exhaled by a vertebrate is a long-range signal that can activate a hungry female from tens of meters away, but it is not host-specific, since any breathing animal produces it. Skin odors carry the identity of a particular host but operate at shorter ranges. Heat and humidity become informative only at close quarters, and visual cues dominate in bright conditions. Because no single cue suffices across the entire journey, mosquitoes must stitch together fragments of information, and the authors emphasize that internal states such as hunger, mating status, and egg-development stage, along with learned associations, bridge the temporal gaps between cues encountered at different moments.

To explain how this stitching happens, the review outlines three sensory architectures that can contribute to host recognition. The first is feedforward multisensory integration, in which signals from different modalities converge in higher brain centers such as the antennal lobe, the lateral horn, and the mushroom body, producing a combined representation of the host. The second is cross-modal gating, in which one sensory channel modulates the sensitivity of another; the classic example is the way carbon dioxide primes the olfactory system to respond more strongly to skin odors. The third, and arguably the most conceptually important, is closed sensorimotor feedback: a mosquito’s own movements change the sensory input it encounters next, so flying upwind toward a plume, casting sideways when the plume is lost, and steering during landing are all acts of active sensing. The insect is not a passive receiver of stimuli but an agent that structures its own perceptual world through action.

This active-sensing perspective carries a technical implication that the authors highlight: host seeking cannot be fully understood by presenting mosquitoes with fixed stimuli in a wind tunnel and recording their choices. Behavior unfolds over seconds to minutes within a single host-seeking bout, and the trajectory of the insect determines which cues it samples and in what order. Sensorimotor dynamics therefore create a loop in which perception guides movement and movement reshapes perception. The review argues that future experiments should be designed to probe this loop directly, for example by tracking how mosquitoes modulate their flight patterns to resolve ambiguous plumes or how they adjust probing behavior on the skin in response to the thermal and chemical feedback they receive from each attempt.

The synthesis also examines how infection changes the picture. Pathogens such as dengue virus, Zika virus, and West Nile virus can modify the host-derived sensory signals that a mosquito encounters, and they can also alter the mosquito’s own responsiveness, probing behavior, feeding persistence, locomotion, and neuromodulation. The authors are careful to grade the evidence. Studies showing that infected hosts or infected mosquitoes differ in relevant traits provide association. Experiments that causally manipulate the pathogen or the mosquito’s physiology establish modulation. Only in a smaller subset of systems do the observed patterns fit what would be expected of adaptive manipulation, in which the pathogen benefits specifically from increased transmission. This tiered framing matters because claims of manipulation are easy to overstate, and the review provides a vocabulary for distinguishing strong from weak inference.

One of the most consequential findings the review consolidates is that infection can reshape the odor landscape itself. Work on dengue and Zika, for instance, has shown that infection can change the volatile chemicals emitted by host skin, making infected individuals more attractive to mosquitoes in ways that plausibly enhance transmission. Conversely, the mosquito’s own infection status can alter how its nervous system processes those cues. Because the extrinsic incubation period, the time a pathogen needs to become transmissible, must align with the mosquito’s blood-feeding schedule, even modest infection-associated shifts in host-seeking or feeding behavior can have disproportionate effects on epidemiological outcomes. The review stresses that these behavioral changes occur on timescales of seconds to minutes within a feeding bout, while transmission emerges over much longer timescales, and connecting the two levels remains an open challenge.

Redundancy emerges as a recurring theme with direct practical consequences. Because host recognition is multimodal, knocking out a single sensory pathway often fails to abolish host seeking. Mosquitoes with impaired carbon dioxide detection can still locate hosts using skin odors and heat; disrupting one family of odorant receptors does not silence the ionotropic receptor channel or the trigeminal-like pathways that detect thermal and humidity cues. This sensory compensation explains why many laboratory interventions, including repellents such as DEET and IR3535 and genetic manipulations of receptor co-receptors such as Orco, show reduced or context-dependent performance in the field. The review argues that intervention studies should evaluate whole-animal phenotypes and mosquito-human contact rates, not just responses at the receptor level, because the intact animal can route around a blocked pathway.

Ecological context is the second major caveat the authors raise for control strategies. Field studies consistently show that the effectiveness of attractant-baited traps, spatial repellents, and odor-based interventions depends on the local environment, the composition of competing host odors, wind conditions, and the species and physiological state of the local mosquito population. A lure that outperforms a human in a semi-field enclosure may fail in a village where natural host cues are abundant and varied. The review therefore proposes a tiered evaluation framework spanning receptor-level mechanisms, whole-animal behavior, effects on mosquito-human contact, and ultimately transmission or disease endpoints, and it warns that laboratory results should not be extrapolated to field performance without explicit testing across contexts.

The microbiome adds yet another layer of complexity. Skin microbiota shape the volatile profile that makes one human more attractive to mosquitoes than another, and the mosquito’s own microbial community can influence its olfactory sensitivity and feeding behavior. The review integrates this evidence into the multimodal framework, suggesting that microbiome-mediated variation in host odors and vector competence represents a modifiable component of the transmission cycle. Combined with the growing recognition that learning allows mosquitoes to adjust their host preferences based on experience, the picture that emerges is of a vector whose host-seeking behavior is plastic at multiple levels: neural, microbial, and experiential.

The review closes by generating testable predictions for active sensing, sensory compensation, infection-associated modulation, and the persistence of intervention effects across laboratory and field settings, and it identifies unresolved sites of neural convergence in the mosquito brain as priorities for future research. For a field in which mosquito-borne diseases such as malaria, dengue, and West Nile fever continue to impose enormous burdens, the message is clear: durable transmission control will come not from blocking a single cue but from understanding the full sensorimotor loop that connects a flying insect to its next blood meal. By mapping that loop, from plume-following flight to the final probing of the skin, and by specifying where pathogens intervene within it, the authors offer both a conceptual framework and a practical roadmap for the next generation of vector-control research.

Subject of Research: Multimodal sensory integration and active sensing in mosquito host recognition and its implications for pathogen transmission control

Article Title: Multimodal host recognition in mosquitoes: sensory integration, active sensing, and transmission control

Article References: Liu, Z., Shu, Z., Bai, Y., Zhang, T., Shi, H., Zhang, D., Liu, G., & Jin, Y. (2026). Multimodal host recognition in mosquitoes: sensory integration, active sensing, and transmission control. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07702-9

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07702-9

Keywords: mosquitoes, host seeking, multisensory integration, active sensing, carbon dioxide, odorant receptors, dengue virus, Zika virus, West Nile virus, pathogen-vector interactions, vector control, sensory neurobiology

Researchers at the University of Liverpool, working with Richard Wall of the University of Bristol, carried out an extraordinarily intensive sampling campaign at Lyme Park in northern England. Every month from January to December 2022, the team dragged a fabric blanket across fixed transects at four-hour intervals, completing full 24-hour sampling cycles. This design allowed them, for the first time, to separate seasonal variation in tick activity from daily, or diel, variation, two dimensions of behaviour that previous studies had almost always examined in isolation. Because the sampling rounds captured ticks actively questing, that is, climbing vegetation with outstretched forelegs to ambush passing hosts, the counts represent genuine host-seeking behaviour rather than simple abundance.

The headline finding is that questing activity in I. ricinus is predominantly nocturnal. Densities of host-seeking ticks were highest during the dark hours of the sampling cycle, and statistical modelling confirmed that darkness itself was a positive predictor of the number of questing nymphs. This is a striking departure from the popular image of ticks as creatures that latch onto walkers in broad daylight, and it has immediate implications for how people, pets and wildlife encounter infected ticks in the field.

The second major moderator of activity was atmospheric moisture, captured by a single, elegant variable known as the saturation deficit. Saturation deficit combines air temperature and relative humidity into a measure of how strongly the air draws water from living tissue, and it is widely used by entomologists to describe desiccation stress in small terrestrial arthropods. Because ticks lack efficient water-conservation mechanisms and must periodically rehydrate within the humid microclimate of the soil and leaf litter, high saturation deficit effectively forces them off the vegetation and into protective refuges. In the new study, the density of questing nymphs was negatively associated with saturation deficit, meaning that hot, dry conditions suppressed host-seeking even when the season was otherwise favourable.

Crucially, the researchers showed that the strength of the nocturnal activity pattern itself varied with the seasonal moisture environment. Night-time questing was most evident in nymphs during months with high saturation deficit, when daytime conditions were too punishing for ticks to remain exposed. In cooler or wetter periods, when desiccation stress was lower, activity was distributed more evenly across the day. In other words, darkness does not simply switch ticks on; rather, harsh daytime climates push their activity into the night, and benign climates allow it to spread out. This interaction between the daily light cycle and seasonal moisture availability had not previously been demonstrated under natural field conditions for this species.

To untangle these effects, the team analysed their 24-hour, year-round dataset using Generalised Linear Mixed Modelling, a statistical framework well suited to count data with repeated measures. Mixed models allowed the investigators to account for the structure of the design, in which the same transects were sampled month after month at identical clock times, while testing the independent contributions of darkness, temperature, humidity and saturation deficit to tick density. The modelling confirmed that the negative effect of saturation deficit and the positive effect of darkness on questing nymph density were robust after controlling for the sampling structure, giving confidence that the observed rhythms reflect biology rather than artefacts of the schedule.

The seasonal dimension of the results was broadly reassuring for the field. The annual pattern of activity, with questing peaking in the warmer months and collapsing through winter, was largely consistent with previously published data on European tick phenology. Larvae, nymphs and adults each showed characteristic seasonal windows of host-seeking, reflecting the developmental timing that determines which life stages pose a threat at any given time of year. Nymphs, the stage most often implicated in transmitting Borrelia bacteria and tick-borne encephalitis virus to humans, dominated the datasets in the ways that surveillance specialists have come to expect.

What makes the study transformative is not the seasonal story but the daily one. Diel patterns in tick behaviour have been chronically understudied, largely because most tick surveillance is conducted during working hours, typically between mid-morning and late afternoon. If ticks quest mainly at night, or shift their activity into nocturnal windows during dry spells, then standard daytime dragging may systematically misestimate both true abundance and true biting risk. The authors point out that these commonly overlooked daily rhythms have important implications for estimating abundance in scientific research and surveillance programmes, and for interpreting how hazard varies across the day rather than across the year alone.

There are also ecological consequences for the transmission of pathogens among wildlife. Different host species are active at different times: birds, small mammals and deer partition the 24-hour cycle in ways that determine which hosts a nocturnal tick is most likely to encounter. If I. ricinus concentrates its host-seeking in the dark, the feeding opportunities available to it, and therefore the transmission circuits available to the pathogens it carries, may be structured by the clock as much as by the calendar. Reservoir hosts that forage at night could contribute disproportionately to infection cycles, while daytime-active animals, including humans, may benefit from the desiccation-driven suppression of tick activity during hot, dry daytime conditions. Understanding these synchronies could sharpen models of disease emergence and inform the timing of interventions, from acaricide application to public health messaging about when and where exposure risk peaks.

For the public, the practical message is nuanced rather than alarmist. Tick bites remain possible at any hour, and risk is shaped locally by habitat, vegetation and recent weather. But the study suggests that people walking in tick habitat during cool, humid evenings and overnight periods may face greater exposure than conventional advice implies, while hot, dry middays may offer comparatively lower risk, not because ticks are absent but because they are sheltering from the desiccating air. Dog walkers and other pet owners, whose animals often roam at dawn and dusk, should take particular note. As climate change alters temperature and humidity regimes across Europe, the seasonal windows and daily rhythms of tick activity are likely to shift in ways that current, daylight-biased surveillance is poorly equipped to detect. This year-round, round-the-clock field study offers a methodological template for closing that blind spot, and a timely reminder that the ecology of one of Europe’s most consequential disease vectors unfolds largely after dark.

Subject of Research: Seasonal and diel environmental drivers of host-seeking (questing) behaviour in the European tick vector Ixodes ricinus.

Article Title: Seasonal and diel environment effects on host-seeking behaviour in the European tick vector, Ixodes ricinus

Article References: Noll, M., Wall, R., Makepeace, B. L., & Rose Vineer, H. (2026). Seasonal and diel environment effects on host-seeking behaviour in the European tick vector, Ixodes ricinus. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07679-5

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07679-5

Keywords: Ixodes ricinus, ticks, questing behaviour, host-seeking, saturation deficit, diel activity, seasonal activity, vector-borne disease, Lyme borreliosis, tick surveillance, Parasites & Vectors, field study