Artificial Light at Night Increases Aedes aegypti Mosquito Biting Behavior with Implications for Arboviral Disease Transmission

Modeling urban wasp nest occurrences using 119 fire service reports, LiDAR, and hyperspectral imagery: The role of green spaces and structural factors

The increasing presence of wasp nests in urban areas raises ecological, economic, and public safety concerns. This study integrates 10 years (2014-2023) of data from 119 fire service reports, high-resolution LiDAR-derived structural information, hyperspectral imagery, and urban microclimate analysis to examine the spatial distribution and key environmental factors influencing wasp nest occurrences in Gwacheon, South Korea. The results indicate a 4.23-fold increase in wasp nest incidents over the past decade, highlighting the increasing prevalence of urban wasp populations. Analysis of fire service reports classified nest occurrence types into four categories: artificial structures (28.2%), natural environments (10.5%), subterranean environments (1.0%), and underground structures (0.13%). The majority of wasp nests were found in artificial structures, particularly in low-rise buildings, demonstrating a strong correlation between nesting preferences and urban structural characteristics. MaxEnt species distribution modeling (AUC = 0.797) identified proximity to green spaces (within 170 m) as the strongest predictor of wasp nest occurrences, followed by building height and shadow relief. Both fire service reports and model predictions confirmed that low-rise buildings (2-5 m) served as the primary nesting sites, emphasizing the role of structural factors in habitat selection. Additionally, urban microclimates around 37 °C promoted nest establishment, whereas extreme temperatures had a negative impact. These findings highlight the importance of high-resolution spatial, ecological, and social data in proactively identifying high-risk urban areas for wasp nest formation. This study proposes an integrated management strategy that considers spatial, ecological, and social factors for effective wasp mitigation. By leveraging long-term incident reports, predictive modeling, and participatory data, urban planners and policymakers can develop targeted interventions that mitigate wasp-related risks while promoting urban biodiversity conservation.

Aedes aegypti reproductive aspects: constant light significantly affects the embryonic development

BACKGROUND

The importance of the mosquito Aedes aegypti as a vector of arboviruses like dengue, Zika, and chikungunya justifies the interest in investigating this species' physiology and reproductive biology. For the maintenance and expansion of Ae. aegypti populations, copulation, oogenesis, female oviposition capacity, embryo development and larval hatching are crucial processes regulated by biological clocks. Many of these parameters have currently been investigated under environmental and laboratory conditions. However, there are specific gaps regarding the effect of light on these critical reproductive aspects. In this study, the influence of light on some aspects of Ae. aegypti biology was evaluated.

OBJECTIVES

We investigated, in laboratory conditions, the effects of constant light on Ae. aegypti reproductive features: spermathecal content, embryo morphology, females' fecundity, and egg viability.

METHODS

Morphological and physiological assays were performed using Ae. aegypti females and eggs obtained from forced egg laying. The reproductive aspects were analysed under constant light (LL = light/light) and light/dark cycles (LD12:12 = 12 h of light and 12 h of dark).

FINDINGS AND MAIN CONCLUSIONS

Our results proved the negative effect of constant light on egg production (decreasing the fecundity) and embryonic development (causing a drop in egg viability and perceptive damage in the embryos). The results presented here bring new information on the impacts that a source of constant light may have on the reproductive biology of Ae. aegypti.

Time-of-day changes in permethrin susceptibility and metabolic gene expression in Florida Aedes aegypti (Diptera: Culicidae)

Aedes aegypti (Linnaeus) is the principal mosquito vector for many of the most medically significant arboviruses that threaten global public health. A better understanding of time-of-day variation in insecticide resistance mediated by detoxifying enzymes in Ae. aegypti could allow for targeted insecticide applications when susceptibility is highest and the upregulation of detoxification enzymes is lowest. Using a susceptible and metabolically resistant field Ae. aegypti strain from Florida, we investigated simulated photoperiodic changes in permethrin susceptibility and upregulation of detoxification enzymes by measuring permethrin LD50 and expression of detoxification genes (GSTE7, GSTE2, CCEae3A, CYP9J28, and CYPBB2) for both strains every 4 h over a 24 h (12:12 h light: dark) cycle. We found that in both Ae. aegypti strains, permethrin susceptibility was lower during the day as compared to evening, with susceptibility lowest at dusk (18:00) and highest between 02:00 and 14:00. Although no significant changes in gene expression over time were observed in the susceptible Ae. aegypti strain, we documented increased expression of all investigated detoxification genes in the metabolically resistant field Ae. aegypti strain during the night (18:00 to 02:00) as compared to the day (06:00 to 14:00). These data suggest that permethrin applications made between midnight and dawn (06:00) may be more effective against Ae. aegypti as compared to applications made at dusk (approximately 18:00).

Perceived causes and solutions for malaria prevalence among seasonal migrant workers in Northwest Ethiopia: a qualitative study

BACKGROUND

Seasonal migrant workers are at increased risk of malaria and can play a substantial role in transmitting the disease to receptive areas. Assessments conducted among these workers showed a high prevalence of malaria. This qualitative study aimed to explore the contributing factors and challenges to the high malaria prevalence among seasonal migrant workers in agricultural farm areas. The study also sought to identify potential solutions.

METHODS

A descriptive phenomenological approach was employed to investigate the perceived causes, challenges, and solutions related to malaria prevalence among seasonal migrant workers in the development corridors of southwest Ethiopia. This approach emphasizes describing experiences as they are, without researcher interpretation. Data were gathered from 24 individuals purposefully selected for their close involvement with seasonal migrant workers and their experience with malaria issues in agricultural farm areas. Open-ended questions were used, and interviews were conducted in safe, quiet settings. Data management was performed using Open Code software version 4.03, and thematic analysis was applied to the contents.

RESULTS

The study findings identified origin from highland areas, low health-seeking behaviour, working at night, and lack of use of long-lasting insecticidal nets (LLINs) as the perceived causes of high malaria prevalence among seasonal migrant workers by the study participants. Limited collaboration among stakeholders, a lack of migrant-friendly malaria prevention strategies, and inconsistent support for medical supplies were challenges highlighted by the key informants. Therefore, seasonal migrant workers were faced with high risk of malaria due to factors such as lack of immunity, delayed treatment, exposure to mosquitoes, and limited prevention efforts. Addressing these challenges is crucial for reducing malaria prevalence among this vulnerable population.

CONCLUSION

The study findings highlighted the need for targeted interventions to address the specific factors contributing to high malaria prevalence among seasonal migrant workers and to overcome the challenges in implementing effective malaria prevention strategies in this vulnerable population. Further study should be conducted to include the views and positions of seasonal migrant workers, owners of the farm areas, host communities, and political leaders.

Chemical Profiling, Sensory Qualities, and Bioactivities of Essential Oils Obtained from Aloysia citrodora and Bursera graveolens Ecuadorian Plants Against the Mosquito Aedes albopictus (Skuse) (Diptera: Culicidae)

The mosquito Aedes albopictus is a vector of several harmful viruses, necessitating the development of safer and more sustainable repellents than DEET. This study evaluated the potential of plant-based EOs extracted via steam distillation from Aloysia citrodora and Bursera graveolens plants harvested in Ecuador. A. citrodora EO exhibited a high sensory pleasantness with a citral-like aroma, while B. graveolens EO had lower sensory appeal due to off-flavors. At 200 µL L-1, B. graveolens EO demonstrated strong ovideterrent activity, reducing egg laying by 64%, whereas A. citrodora EO displayed the highest larvicidal activity with an LC50 value of 88.54 µL L-1. Both EOs, applied at 0.20 µL cm-2 on human skin, provided comparable repellency for over 45 min. The RD50 values were 0.104 µL cm-2 for A. citrodora EO and 0.136 µL cm-2 for B. graveolens EO. When compared to DEET at 0.04 µL cm-2, no significant differences in repellency were observed within the first 15 min post-application. These findings suggest that both EOs are effective alternatives to synthetic repellents, and A. citrodora EO emerges as a promising candidate due to its superior sensory attributes and larvicidal activity.

Biting Hour and Host Seeking Behavior of Aedes Species in Urban Settings, Metema District, Northwest Ethiopia

BACKGROUND

Aedes species transmit arboviral diseases, such as dengue, chikungunya, yellow fever, and Zika. The diseases cause severe sickness, mortality, and economic losses. This study describes the biting hour and host-seeking behavior of Ae. aegypti and Ae. vittatus in three towns. Recently, chikungunya and dengue infections were reported in the study sites.

METHODS

Biting hour and host-seeking behaviors of Ae. aegypti and Ae. vittatus were studied from June to September 2023, in Genda-Wuha, Kokit, and Metema-Yohannes towns, Metema district, Northwest Ethiopia. CDC-LT traps were set running indoors and outdoors for 24 h closer to humans sleeping inside unimpregnated mosquito nets. At the same time, CDC-LT traps were set running overnight closer to domestic animals' shelters located within a 50-m radius of the main residence. Mosquitoes trapped in CDC-LT were collected every hour. The study was conducted four times in each town during the wet season. A chi-square test was employed to examine biting hour and host-seeking behavior.

RESULTS

Aedes aegypti was observed to be highly exophilic and active during the daylight hours. Aedes aegypti exhibited a peak biting rate between 07:00 and 08:00 with the biting rate of 4.5/person/hour followed by from 17:00 pm to 18:00 pm with the biting rate of 3.75/person/hour. The hourly biting rate of Ae. aegypti differed significantly. Its peak indoor biting rate was from 19:00 to 20:00 with the rate of 2.00 bites/person/hour followed by from 08:00 to 09:00 with the rate of 1.50 bites/person/hour and the biting rates differed significantly across the hours (F = 240.046; p = 0.001). Aedes vittatus also exhibited a biting rate similar to that of Ae. aegypti. Both Ae. aegypti and Ae. vittatus were abundantly collected from nearby human sleeping arrangements than from the shelters of cattle, sheep, goats, and donkeys. The highest proportions of Ae. aegypti (91.21%) and Ae. vittatus (89.87%) were unfed.

CONCLUSIONS

Aedes aegypti and Ae. vittatus exhibited peak biting rates during morning and early night hours that aligned with the active daily routine practices of the local community. This could potentially expose the inhabitants to viral diseases transmitted by Ae. aegypti and Ae. vittatus.

A primary school-based dengue solution model for post-COVID-19 in southern Thailand: Students understanding of the dengue solution and larval indices surveillance system

One of the consequences of the COVID-19 lockdown is that it hinders school-based dengue management interventions. This is due to the closure of schools and the limited availability of online lessons in certain schools. Conversely, the level of basic understanding that primary school children have about the condition is directly related to their likelihood of getting it and their ability to modify their behaviour to prevent it. Thus, the study aims to assess the understanding and develop a school-based model intervention for dengue solutions and larval indices surveillance systems suitable for primary schools. The study used a purposive and convenience technique to recruit participants in the Keawsan sub-district in Nabon district, Nakhon Si Thammarat province, Thailand. An applied community participatory action research (CPAR) design was used to develop a school-based model intervention. The pre-test result shows that more than 90% and 100% of the students have a poor understanding of dengue solutions (UDS) and larval indices surveillance systems (ULISS), respectively. The students with good scores on UDS increased from 2.9% to 54.6% after the intervention, and there is still a prevalent lack of good understanding among more than 85% of the students on ULISS. Meanwhile, gender, class, and school significantly influence (p <0.05) UDS and ULISS among students in either the pre-test or post-test. Based on the thematic analysis, it was determined that the students had learned about dengue fever transmission, dengue mosquitoes, container index calculation, dengue symptoms, and how to prevent dengue mosquitoes, among other topics. Overall, it was discovered that the trained students could convey their knowledge of the dengue solution and the larval indices surveillance system to other students. We recommend that further ULISS training be provided for schoolchildren in more simple terms that they can understand.

Intra-species quantification reveals differences in activity and sleep levels in the yellow fever mosquito, Aedes aegypti

Aedes aegypti is an important mosquito vector of human disease with a wide distribution across the globe. Climatic conditions and ecological pressure drive differences in the biology of several populations of this mosquito species, including blood-feeding behaviour and vector competence. However, no study has compared activity and/or sleep among different populations/lineages of Ae. aegypti. Having recently established sleep-like states in three mosquito species with observable differences in timing and amount of sleep among species, we investigated differences in activity and sleep levels among 17 Ae. aegypti lines drawn from both its native range in Africa and its invasive range across the global tropics. Activity monitoring indicates that all the lines show consistent diurnal activity, but significant differences in activity level, sleep amount, number of sleep bouts and bout duration were observed among the lines. The variation in day activity was associated with differences in host preference and ancestry for the lineages collected in Africa. This study provides evidence that the diurnal sleep and activity profiles for Ae. aegypti are consistent, but there are significant population differences for Ae. aegypti sleep and activity levels and interactions with host species may significantly impact mosquito activity.

Light pollution disrupts seasonal reproductive phenotypes and reduces lifespan in the West Nile vector, Culex pipiens

Females of the Northern House mosquito, Culex pipiens, are important disease vectors as they transmit pathogens including West Nile virus. These females survive the winter by entering diapause, a state of dormancy, characterized by the accumulation of lipids, cessation of blood-feeding, and reproductive arrest. Diapause is cued by photoperiod, so as days become short in late summer and early fall, female Cx. pipiens prepare to overwinter and disease transmission decreases. We previously demonstrated that Artificial light at night (ALAN) causes female Cx. pipiens to avert diapause and continue to blood-feed when reared under short-day conditions. Additionally, light pollution alters seasonal differences in mosquito activity and nutrient reserves. However, it is unclear how exposure to ALAN affects blood-feeding and fecundity in long-day reared females, as well as the survival of Cx. pipiens exposed under both short and long-day conditions. In this study, we hypothesized that females exposed to ALAN in long-day conditions would have a lower proclivity to blood-feed, reduced fecundity, and reduced survival. Results from our lab-based experiments demonstrate that females exposed to ALAN in long-day conditions were less likely to blood-feed but were more fecund than long-day reared females that were not exposed to ALAN, and that ALAN exposure did not affect lifespan of long-day reared females. Additionally, we hypothesized ALAN exposure under short-day conditions would reduce survival, and our data supports this hypothesis. Overall, our results demonstrate that ALAN is an important urban stressor that has the potential to affect reproduction and lifespan in mosquitoes, and therefore has the potential to create evolutionary tradeoffs.

Spatiotemporal distribution, environmental correlation and health risk analysis of Culex tritaeniorhynchus (Diptera: Culicidae) in Beijing, China

The Culex tritaeniorhynchus Giles, 1901 (Diptera: Culicidae) is major vector of Japanese encephalitis (JE) in China, and this study aimed to uncover the vector's spatiotemporal distribution and environmental correlation in Beijing. In study area, the Remote Sensing (RS), Global Position System (GPS), and Geographic Information System (GPS) were used to clarify the distribution characteristics of vector on spatial and temporal scales, and regressions analysis of cross-sectional study was performed to detect the environmental factors linked with the density and presence of Cx. tritaeniorhynchus. In study area, the scenic area was the major environmental area for breeding of the vector, August was the primary peak month, the new urban development area (NUDA) was major distribution subarea of Beijing, and the vector could be detected throughout the subarea of Beijing from June to September. In the scenic area, the total value of light index within buffer zones of 100 m (LT_100) and the total value of NDVI index within buffer zones of 800 m (NDVI_800) determined whether there was a positive or negative vector in the trapping sites, and the total value of NDVI index within buffer zones of 100 m (NDVI_100) and LT_100 was linked to the density of the vector. Our findings provide better insight into the spatio-temporal distribution pattern, associated environmental risk factors, and health risk of vector in Beijing. Based on the results here, we could predict the risk of JE and create and implement location-specific JE prevention and control measures to prevent future risks during the urbanization advancement of Beijing.

Only incandescent light significantly decreases feeding of Anopheles funestus s.s. (Diptera: Culicidae) mosquitoes under laboratory conditions

Recent work has demonstrated that exposure to artificial light at night (ALAN) may alter mosquito feeding behavior and so must be considered a moderator of vector-borne disease transfer. Anopheles funestus mosquitoes are a primary malaria vector in sub-Saharan Africa, but no study to date has tested the impact of ALAN on their feeding behavior. Here we test if the exposure to commonly used household lights (compact fluorescent lights, light-emitting diodes, and incandescent lights) alters Anopheles funestus feeding. Mated, unfed female mosquitoes were exposed to a light treatment, at the onset of darkness, followed by a blood-feeding assay. The light treatments consisted of a 30-min light pulse of one of the three household lights, each in individual experimental containers, versus controls. All three household lights resulted in a reduction in the percentage of females taking a blood meal, but only mosquitoes exposed to incandescent light showed a statistically significant reduction in feeding of 19.6% relative to controls which showed a 42.8% feeding rate. Our results suggest that exposure to some household lights during the night may have an immediate inhibitory effect on Anopheles funestus feeding. By helping identify which light types lead to a suppression of feeding, the findings of this study could provide insight necessary to design household lights that can help minimize mosquito feeding on humans.

Progress towards understanding the effects of artificial light on the transmission of vector-borne diseases

Artificial light at night (ALAN) is a common form of light pollution worldwide, and the intensity, timing, duration, and wavelength of light exposure can affect biological rhythms, which can lead to metabolic, reproductive, and immune dysfunctions and consequently, host-pathogen interactions. Insect vector-borne diseases are a global problem that needs to be addressed, and ALAN plays an important role in disease transmission by affecting the habits and physiological functions of vector organisms. In this work, we describe the mechanisms by which ALAN affects host physiology and biochemistry, host-parasite interactions, and vector-borne viruses and propose preventive measures for related infectious diseases to minimize the effects of artificial light on vector-borne diseases.

Repelling Aedes aegypti mosquitoes with electric fields using insulated conductor wires

BACKGROUND

The control and prevention of mosquito-borne diseases is mostly achieved with insecticides. However, their use has led to the rapid development and spread of insecticide resistance worldwide. Health experts have called for intensified efforts to find new approaches to reduce mosquito populations and human-mosquito contact. A promising new tool is the use of electrical fields (EFs), whereby mosquitoes are repelled by charged particles in their flight path. Such particles move between two or more conductors, and the use of uninsulated copper or aluminum plates as conductors has been proven to be effective at repelling mosquitoes. Here, for the first time, we assess if EFs generated using a single row of insulated conductor wires (ICWs) can also successfully repel mosquitoes, and whether mosquitoes are equally repelled at the same EF strength when the electrodes are a) orientated differently (horizontal vs. vertical placement), and b) spaced more apart.

METHODOLOGY/PRINCIPAL FINDINGS

Over a period of 23 hours, the number of host-seeking female Aedes aegypti mosquitoes that were successfully repelled by EFs, using ICWs, at EF strengths ranging from 0 kV/cm (control) to 9.15 kV/cm were quantified. Mosquitoes were released inside a 220×220×180 cm room and lured into a BG-Pro trap that was equipped with a BG-counter and baited with CO2 using dry ice. Mosquitoes had to pass through an EF window, that contained a single row of ICWs with alternating polarity, to reach the bait. The baseline interaction between EF strength and repellency was assessed first, after which the impact of different ICW orientations and ICW distances on repellency were determined. Over 50% of mosquitoes were repelled at EF strengths of ≥ 3.66 kV/cm. A linear regression model showed that a vertical ICW orientation (vertical vs. horizontal) had a small but insignificant increased impact on mosquito repellency (p = 0.059), and increasing ICW distance (while maintaining the same EF strength) significantly reduced repellency (p = 0.01).

CONCLUSIONS/SIGNIFICANCE

ICWs can be used to generate EFs that partially repel host-seeking mosquitoes, which will reduce human-mosquito contact. While future studies need to assess if (i) increased repellency can be achieved, and (ii) a repellency of 50-60% is sufficient to impact disease transmission, it is encouraging that EF repellency using ICWs is higher compared to that of some spatial repellent technologies currently in development. This technology can be used in the housing improvement toolkit (i.e. preventing mosquito entry through eaves, windows, and doors). Moreover, the use of cheap, over-the-counter ICWs will mean that the technology is more accessible worldwide, and easier to manufacture and implement locally.

Investigation of risk factors for household-based dengue virus infection in Borobudur Subdistrict, Magelang, Indonesia

Introduction

Dengue infection poses a serious threat to global public health, including Indonesia. The rapid spread and significant economic impact are crucial concerns for control efforts. Investigating risk factors of dengue virus infection is necessary to formulate effective strategies, particularly at the household level. This study aims to investigate contributing risk factors to dengue virus transmission in the Borobudur Subdistrict, Magelang, Indonesia, an area with persistently high dengue infection mortality rates.

Methods

This study adopted a case-control design and utilized secondary data collected from six villages in the Borobudur Subdistrict. A total of 111 households (37 cases and 74 controls) participated in the study and completed a questionnaire encompassing: 1) Sociodemographic data; 2) Healthy housing components; 3) Sanitation and behavioral components; and 4) Dengue infection prevention practices. Data were analyzed bivariately using statistical software to identify differences in group proportions.

Results

The findings of this study indicate that the presence of stagnant water (odds ratio [OR]: 5.02) and mosquito larvae (OR: 4.80) around the house, morning sleep habits (OR: 6.97), and lack of participation in anti-dengue programs (OR: 3.23) are significant risk factors (p<0.05) for dengue infection. However, no significant differences (p>0.05) were found in healthy housing components between the case and control groups.

Conclusions

This study has identified contributing risk factors to dengue virus transmission in the Borobudur Subdistrict. These results can serve as a foundation for designing more effective intervention programs for dengue infection and future prevention efforts.

Circadian and daily rhythms of disease vector mosquitoes

Mosquitoes express a rich repertoire of daily 24-hour rhythms in biochemistry, physiology, and behavior. The nocturnal Anopheles and Culex and diurnal Aedes mosquitoes are major vectors of human disease, transmitting parasites and arboviruses, such as malaria and dengue. In this review, we explore the role that 24-hour diel and circadian rhythms play in shaping the temporal life of the mosquito. We focus on recent advances in our understanding of behavioral rhythms, focusing on locomotor/flight activity, host-seeking, biting/blood feeding, and mating. We examine the molecular circadian clock, photocycle, and light signals, which in combination shape the mosquito 24-hour temporal program. We address species- and sex-specific differences and highlight important selective pressures from dynamically changing environments. This work also provides new insights into disease transmission, insect control, and future experimental design.

The effect of artificial light at night (ALAN) on the characteristics of diapause of Aedes albopictus

BACKGROUND

Recently, the effect of artificial light at night (ALAN) on the physiology and behavior of insects has gradually attracted the attention of researchers and has become a new research topic. Aedes albopictus is an important vector that poses a great public health risk. Further studies on the diapause of Ae. albopictus can provide a basis for new vector control, and it is also worth exploring whether the effect of ALAN on the diapause of Ae. albopictus will provide a reference for the prevention and control of infectious diseases mediated by Ae. albopictus.

METHODS

In this study, we experimentally studied the diapause characteristics of different geographical strains of Ae. albopictus under the interference of ALAN, explored the effect of ALAN on the diapause of Ae. albopictus and explored the molecular mechanism of ALAN on the diapause process through RNA-seq.

RESULTS

As seen from the diapause incidence, Ae. albopictus of the same geographic strain showed a lower diapause incidence when exposed to ALAN. The differentially expressed genes (DEGs) were mainly enriched in signaling and metabolism-related pathways in the parental females and diapause eggs of the ALAN group.

CONCLUSIONS

ALAN inhibits Ae. albopictus diapause. In the short photoperiod induced diapause of Ae. albopictus in temperate strain Beijing and subtropical strain Guangzhou, the disturbance of ALAN reduced the egg diapause rate and increased the egg hatching rate of Ae. albopictus, and the disturbance of ALAN also shortened the life cycle of Ae. albopictus eggs after hatching.

Timely Questions Emerging in Chronobiology: The Circadian Clock Keeps on Ticking

Chronobiology investigations have revealed much about cellular and physiological clockworks but we are far from having a complete mechanistic understanding of the physiological and ecological implications. Here we present some unresolved questions in circadian biology research as posed by the editorial staff and guest contributors to the Journal of Circadian Rhythms. This collection of ideas is not meant to be comprehensive but does reveal the breadth of our observations on emerging trends in chronobiology and circadian biology. It is amazing what could be achieved with various expected innovations in technologies, techniques, and mathematical tools that are being developed. We fully expect strengthening mechanistic work will be linked to health care and environmental understandings of circadian function. Now that most clock genes are known, linking these to physiological, metabolic, and developmental traits requires investigations from the single molecule to the terrestrial ecological scales. Real answers are expected for these questions over the next decade. Where are the circadian clocks at a cellular level? How are clocks coupled cellularly to generate organism level outcomes? How do communities of circadian organisms rhythmically interact with each other? In what way does the natural genetic variation in populations sculpt community behaviors? How will methods development for circadian research be used in disparate academic and commercial endeavors? These and other questions make it a very exciting time to be working as a chronobiologist.

Association between anthropization and rodent reservoirs of zoonotic pathogens in Northwestern Mexico

The world is facing a major pulse of ecological and social changes that may favor the risk of zoonotic outbreaks. Such risk facilitation may occur through the modification of the host's community diversity and structure, leading to an increase in pathogen reservoirs and the contact rate between these reservoirs and humans. Here, we examined whether anthropization alters the relative abundance and richness of zoonotic reservoir and non-reservoir rodents in three Socio-Ecological Systems. We hypothesized that anthropization increases the relative abundance and richness of rodent reservoirs while decreasing non-reservoir species. We first developed an Anthropization index based on 15 quantitative socio-ecological variables classified into five groups: 1) Vegetation type, 2) Urbanization degree, 3) Water quality, 4) Potential contaminant sources, and 5) Others. We then monitored rodent communities in three regions of Northwestern Mexico (Baja California, Chihuahua, and Sonora). A total of 683 rodents of 14 genera and 27 species were captured, nine of which have been identified as reservoirs of zoonotic pathogens (359 individuals, 53%). In all regions, we found that as anthropization increased, the relative abundance of reservoir rodents increased; in contrast, the relative abundance of non-reservoir rodents decreased. In Sonora, reservoir richness increased with increasing anthropization, while in Baja California and Chihuahua non-reservoir richness decreased as anthropization increased. We also found a significant positive relationship between the anthropization degree and the abundance of house mice (Mus musculus) and deer mice (Peromyscus maniculatus), the most abundant reservoir species in the study. These findings support the hypothesis that reservoir species of zoonotic pathogens increase their abundance in disturbed environments, which may increase the risk of pathogen exposure to humans, while anthropization creates an environmental filtering that promotes the local extinction of non-reservoir species.

Light pollution disrupts circadian clock gene expression in two mosquito vectors during their overwintering dormancy

Artificial light at night (ALAN) is an increasingly important form of environmental disturbance as it alters Light:Dark cycles that regulate daily and seasonal changes in physiology and phenology. The Northern house mosquito (Culex pipiens) and the tiger mosquito (Aedes albopictus) enter an overwintering dormancy known as diapause that is cued by short days. These two species differ in diapause strategy: Cx. pipiens diapause as adult females while Ae. albopictus enter a maternally-programmed, egg diapause. Previous studies found that ALAN inhibits diapause in both species, but the mechanism is unknown. As the circadian clock is implicated in the regulation of diapause in many insects, we examined whether exposure to ALAN altered the daily expression of core circadian cloc genes (cycle, Clock, period, timeless, cryptochrome 1, cryptochrome 2, and Par domain protein 1) in these two species when reared under short-day, diapause-inducing conditions. We found that exposure to ALAN altered the abundance of several clock genes in adult females of both species, but that clock gene rhythmicity was maintained for most genes. ALAN also had little effect on clock gene abundance in mature oocytes that were dissected from female Ae. albopictus that were reared under short day conditions. Our findings indicate that ALAN may inhibit diapause initiation through the circadian clock in two medically-important mosquitoes.

Scaling artificial light at night and disease vector interactions into socio-ecological systems: a conceptual appraisal

There is burgeoning interest in how artificial light at night (ALAN) interacts with disease vectors, particularly mosquitoes. ALAN can alter mosquito behaviour and biting propensity, and so must alter disease transfer rates. However, most studies to date have been laboratory-based, and it remains unclear how ALAN modulates disease vector risk. Here, we identify five priorities to assess how artificial light can influence disease vectors in socio-ecological systems. These are to (i) clarify the mechanistic role of artificial light on mosquitoes, (ii) determine how ALAN interacts with other drivers of global change to influence vector disease dynamics across species, (iii) determine how ALAN interacts with other vector suppression strategies, (iv) measure and quantify the impact of ALAN at scales relevant for vectors, and (v) overcome the political and social barriers in implementing it as a novel vector suppression strategy. These priorities must be addressed to evaluate the costs and benefits of employing appropriate ALAN regimes in complex socio-ecological systems if it is to reduce disease burdens, especially in the developing world. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Sleep: An Essential and Understudied Process in the Biology of Blood-Feeding Arthropods

Understanding the biology of blood-feeding arthropods is critical to managing them as vectors of etiological agents. Circadian rhythms act in the regulation of behavioral and physiological aspects such as blood feeding, immunity, and reproduction. However, the impact of sleep on these processes has been largely ignored in blood-feeding arthropods, but recent studies in mosquitoes show that sleep-like states directly impact host landing and blood feeding. Our focus in this review is on discussing the relationship between sleep and circadian rhythms in blood-feeding arthropods along with how unique aspects such as blood gluttony and dormancy can impact sleep-like states. We highlight that sleep-like states are likely to have profound impacts on vector-host interactions but will vary between lineages even though few direct studies have been conducted. A myriad of factors, such as artificial light, could directly impact the time and levels of sleep in blood-feeding arthropods and their roles as vectors. Lastly, we discuss underlying factors that make sleep studies in blood-feeding arthropods difficult and how these can be bypassed. As sleep is a critical factor in the fitness of animal systems, a lack of focus on sleep in blood-feeding arthropods represents a significant oversight in understanding their behavior and its role in pathogen transmission.

Understanding knowledge, attitude and perception of Rift Valley fever in Baringo South, Kenya: A cross-sectional study

Rift Valley fever (RVF) is a mosquito-borne viral hemorrhagic disease that affects humans and livestock. In Kenya, the disease has spread to new areas like Baringo County, with a growing realization that the epidemiology of the virus may also include endemic transmission. Local knowledge of a disease in susceptible communities is a major driver of prevention and control efforts. A cross-sectional survey using a semi-structured questionnaire was conducted in five locations of Baringo South that had reported RVF cases during the last outbreak, to determine the knowledge, attitude and perception of the predominantly agro-pastoralist community to RVF. Knowledge of RVF clinical signs, transmission, risk factors and prevention all contributed to the total knowledge score. Additionally, the respondents' attitude was based on their awareness of the threat posed by RVF and preparedness to take appropriate measures in case of suspected infection. Out of the 300 respondents, 80% had heard about the disease, however, only 9.6% attained at least half of the total knowledge score on RVF. Nevertheless, 86% recognized the threat it posed and knew the appropriate action to take in suspected human and livestock cases (positive attitude). Factors significantly associated with a better knowledge of RVF included higher education level, being Maasai, higher socio-economic index, old age and history of RVF in household members and livestock. Being Maasai and a higher socio-economic index were significantly associated with a positive attitude. The low level of knowledge exhibited by the respondents could be due to progressive loss of interest and information associated with a prolonged inter-outbreak period. This calls for regular awareness campaigns. More emphasis should also be put on educating communities on the role played by the mosquito vector in the epidemiology of RVF. The most promising routes of disseminating this information are radio and community gatherings.

Impact of Human Activities on Disease-Spreading Mosquitoes in Urban Areas

Urbanization is one of the leading global trends of the twenty-first century that has a significant impact on health. Among health challenges caused by urbanization, the relationship of urbanization between emergence and the spread of mosquito-borne infectious diseases (MBIDs) is a great public health concern. Urbanization processes encompass social, economic, and environmental changes that directly impact the biology of mosquito species. In particular, urbanized areas experience higher temperatures and pollution levels than outlying areas but also favor the development of infrastructures and objects that are favorable to mosquito development. All these modifications may influence mosquito life history traits and their ability to transmit diseases. This review aimed to summarize the impact of urbanization on mosquito spreading in urban areas and the risk associated with the emergence of MBIDs. Moreover, mosquitoes are considered as holobionts, as evidenced by numerous studies highlighting the role of mosquito-microbiota interactions in mosquito biology. Taking into account this new paradigm, this review also represents an initial synthesis on how human-driven transformations impact microbial communities in larval habitats and further interfere with mosquito behavior and life cycle in urban areas.

Influence of meteorological and seasonal parameters on the activity of Culicoides paraensis (Diptera: Ceratopogonidae), an annoying anthropophilic biting midge and putative vector of Oropouche Virus in Rondônia, Brazilian Amazon

Biting midges of the genus Culicoides are insects of proven medical and veterinary importance, because of their role in the transmission of viruses, bacteria, protozoa and nematodes. Culicoides paraensis has been considered the main vector of the Oropouche Virus (OROV) in the urban cycle of the disease in the neotropics. Due to the great abundance of Culicoides spp. in the State of Rondônia and its epidemiological history of OROV, we investigated the biting activity in humans, the abundance as a function of meteorological parameters and seasonality, and the detection of OROV. Entomological collections occurred in three municipalities from Brazilian State of Rondônia: Porto Velho, Ariquemes, and Ouro Preto do Oeste. GLMM's were used to determine if Culicoides spp. abundance was predicted by seasonal, diurnal, and meteorological factors. Total RNA was extracted from insects and viral RNA detection was performed using the S segment as the target region of OROV via RT-qPCR. In total, 7,315 individuals were captured and identified as C. paraensis. In the dry season, 1,488 individuals (24.5%) were recorded, 4,591 (75.5%) in the rainy season, with peaks of biting activity between 4pm and 6pm. All variables showed a significative effect on the midge abundance. The rainy season, temperature between 30°C and 32°C and relative air humidity between 75% and 85% were the main predictive parameters for capturing the highest average number of insects. Our results confirm diurnal activity of C. paraensis and its greatest abundance in rainy periods. No sample was positive for the OROV, which could be explained by the virus absence in local human populations, C. paraensis as a minor vector species in the sampled localities, and probable low rate of infection of biting midges. Our findings on hourly and seasonal biting activities can provide support to intervention actions regarding vector control and surveillance of this species. This was the first study to collect and analyze biting midges in a region where human OROV cases had already been detected, but without previous information on entomovirological surveillance.

Light Pollution Disrupts Seasonal Differences in the Daily Activity and Metabolic Profiles of the Northern House Mosquito, Culex pipiens

The Northern House mosquito, Culex pipiens, is an important disease vector, and females are capable of surviving the winter in a state of overwintering diapause. This species' diapause response has been extensively studied, and recent evidence suggests that the circadian clock is involved in measuring seasonal changes in daylength to initiate the diapause response. However, differences in the circadian activity of diapausing and non-diapausing Cx. pipiens have not been thoroughly investigated. Additionally, recent findings indicate that artificial light at night (ALAN) can disrupt mosquito diapause, potentially prolonging the mosquito biting season. We compared the circadian locomotor activity of mosquitoes reared in diapause-averting, long-day conditions and diapause-inducing, short-day conditions with and without ALAN to elucidate the interplay between circadian activity, diapause, and light pollution. We also uncovered metabolic differences between mosquitoes reared under diapausing and non-diapausing photoperiods with and without ALAN by measuring the concentration of protein, fructose, glycogen, water-soluble carbohydrates, and lipids. We found that ALAN exposure altered several diapause-associated phenotypes including slightly, but not significantly, increasing activity levels in short day-reared mosquitoes; and preventing some short day-reared mosquitoes from accumulating lipids. ALAN also significantly reduced glycogen and water-soluble carbohydrate levels in long day-reared mosquitoes. Based on our findings, light pollution may decrease insect fitness by perturbing metabolism, and may also impact several phenotypes associated with insect diapause, potentially extending the mosquito biting season and preventing insects in urban environments from overwintering successfully.

The spectral composition of a white light influences its attractiveness to Culex pipiens mosquitoes

Insect attraction to artificial light can potentially facilitate disease transmission by increasing contact between humans and vectors. Previous research has identified specific wavelength bands, such as yellow and red, that are unattractive to biting flies. However, narrow-band, non-white lights are unsuitable for home lighting use as their very poor color rendering is often considered aesthetically undesirable. The creation of a white light that is unattractive to insects has so far remained elusive. White light can be created by combining a number of narrow-band light-emitting diodes (LEDs). Through choice chamber experiments on Culex pipiens (Cx. pipiens) mosquitoes, we examine whether combining specific wavelength bands has an additive, subtractive or synergistic effect on insect attraction. We show that a white light created by combining narrow-band red, green and blue (RGB) LEDs is less attractive to Cx. pipiens than a broad-spectrum white light; and that a white light created by combining narrow-band blue and yellow LEDs is more attractive than a broad-spectrum white light. White light produced by RGB combinations could therefore serve as a safer and cheaper light in countries where phototactic vectors and vector-borne disease are endemic.

Quantitative Trait Locus Determining the Time of Blood Feeding in Culex pipiens (Diptera: Culicidae)

Mosquitoes and other blood feeding arthropods are vectors of pathogens causing serious human diseases, such as Plasmodium spp. (malaria), Wuchereria bancrofti (lymphatic filariasis), Borrelia burgdorferi (Lyme disease), and viruses causing dengue, Zika, West Nile, chikungunya, and yellow fever. Among the most effective strategies for the prevention of vector-borne diseases are those aimed at reducing human-vector interactions, such as insecticide applications and insecticide-treated bed nets (ITNs). In some areas where ITNs are widely used, behavioral adaptations have resulted in mosquitoes shifting their time of blood feeding to earlier or later in the night when the bed nets are not being employed. Little is known about the genetic basis of these behavioral shifts. We conducted quantitative trait locus (QTL) analysis using two strains of Culex pipiens sensu lato with contrasting blood feeding behaviors, wherein the lab adapted Shasta strain blood feeds at any time of the day or night, while the newly established Trinidad strain feeds only at night. We identified a single locus on chromosome 2 associated with the observed variation in feeding times. None of the core clock genes period, timeless, clock, cycle, PAR-domain protein 1, vrille, discs overgrown, cryptochrome 1, or cryptochrome 2 were located within the QTL region. We then monitored locomotor behavior to determine if they differed in their flight activity. The highly nocturnal Trinidad strain showed little daytime activity while the day-feeding Shasta strain was active during the day, suggesting blood feeding behavior and flight activity are physiologically linked.

Behavioral and postural analyses establish sleep-like states for mosquitoes that can impact host landing and blood feeding

Sleep is an evolutionarily conserved process that has been described in different animal systems. For insects, sleep characterization has been primarily achieved using behavioral and electrophysiological correlates in a few systems. Sleep in mosquitoes, which are important vectors of disease-causing pathogens, has not been directly examined. This is surprising as circadian rhythms, which have been well studied in mosquitoes, influence sleep in other systems. In this study, we characterized sleep in mosquitoes using body posture analysis and behavioral correlates, and quantified the effect of sleep deprivation on sleep rebound, host landing and blood-feeding propensity. Body and appendage position metrics revealed a clear distinction between the posture of mosquitoes in their putative sleep and awake states for multiple species, which correlated with a reduction in responsiveness to host cues. Sleep assessment informed by these posture analyses indicated significantly more sleep during periods of low activity. Night-time and daytime sleep deprivation resulting from the delivery of vibration stimuli induced sleep rebound in the subsequent phase in day and night active mosquitoes, respectively. Lastly, sleep deprivation suppressed host landing in both laboratory and field settings, and impaired blood feeding of a human host when mosquitoes would normally be active. These results suggest that quantifiable sleep states occur in mosquitoes and highlight the potential epidemiological importance of mosquito sleep.

Night Time Extension of Aedes aegypti Human Blood Seeking Activity

This study examined whether Aedes aegypti extends its human blood seeking activity into night hours. Human landing catches (HLC) were conducted hourly from early morning (04:30) to late evening (21:30) in urban and rural sites in Kisumu County in western Kenya, and in Kwale County at the coast. Out of 842 female Ae. aegypti mosquitoes, 71 (8.5%) were collected at night (nocturnal), 151 (17.9%) at twilight (crepuscular), and 620 (73.6%) during the day (diurnal). Three-fold and significantly more Ae. aegypti female mosquitoes were collected during the twilight (crepuscular) hours than night (nocturnal) hours. Significantly more Ae. aegypti female mosquitoes were collected during daytime (diurnal) than night time (nocturnal). In general, the number of mosquitoes collected reduced as darkness increased. Extended time into the night to seek for blood meals enhances chances for Ae. aegypti to contact humans and transmit arboviruses diseases.

Temporal Evaluation of Insecticide Resistance in Populations of the Major Arboviral Vector Aedes Aegypti from Northern Nigeria

To support evidence-based control measures, two Nigerian Aedes populations (BUK and Pantami) were characterised. Larval bioassay using temephos and deltamethrin revealed a significant increase in deltamethrin resistance, with LC50 of 0.018mg/L (resistance ratio compared to New Orleans, RR = 2.250) in 2018 increasing ~6-fold, by 2019 (LC50 = 0.100mg/L, RR = 12.5), and ~11-fold in 2020 (LC50 = 0.198mg/L, RR = 24.750). For the median deltamethrin concentration (0.05mg/L), a gradual decrease in mortality was observed, from 50.6% in 2018, to 44.9% in 2019, and 34.2% in 2020. Extremely high DDT resistance was observed, with <3% mortalities and LT50s of 352.87 min, 369.19 min and 406.94 min in 2018, 2019 and 2020, respectively. Significant temporal increase in resistance was observed towards ƛ-cyhalothrin (a type II pyrethroid) over three years. Synergist bioassays with diethylmaleate and piperonylbutoxide significantly recovered DDT and ƛ-cyhalothrin susceptibility respectively, implicating glutathione S-transferases and CYP450s. Cone bioassays revealed increased resistance to the PermaNet® 3.0, side panels (mortalities of 94% in 2018, 66.4% in 2019, and 73.6% in 2020), while full susceptibility was obtained with the roof of PermaNet® 3.0. The F1534C kdr mutation occurred in low frequency, with significant correlation between heterozygote genotypes and DDT resistance. This temporal increase in resistance is a major challenge for control of this vector of public health importance.

Artificial Light as a Modulator of Mosquito-Borne Disease Risk

Light is a fundamental cue regulating a host of biological responses. The artificial modification thereof demonstrably impacts a wide range of organisms. The use of artificial light is changing in type, extent and intensity. Insect vector-borne diseases remain a global scourge, but surprisingly few studies have directly investigated the interactions between artificial light and disease vectors, such as mosquitoes. Here we briefly overview the progress to date, which highlights that artificial light must be considered as a modulator of mosquito-borne disease risk. We discuss where the mechanisms may lie, and where future research could usefully be directed, particularly in advancing understanding of the biological effects of the light environment. Further understanding of how artificial light may modulate mosquito-borne disease risk may assist in employing and redesigning light regimes that do not increase, and may even mitigate, already significant disease burdens, especially in the developing world.

Epidemiological and virological factors determining dengue transmission in Sri Lanka during the COVID-19 pandemic

With the onset of the COVID-19 pandemic in early 2020 there was a drastic reduction in the number of dengue cases in Sri Lanka, with an increase towards the end of 2021. We sought to study the contribution of virological factors, human mobility, school closure and mosquito factors in affecting these changes in dengue transmission in Sri Lanka during this time. To understand the reasons for the differences in the dengue case numbers in 2020 to 2021 compared to previous years, we determined the association between the case numbers in Colombo (which has continuously reported the highest number of cases) with school closures, stringency index, changes in dengue virus (DENV) serotypes and vector densities. There was a 79.4% drop in dengue cases from 2019 to 2020 in Colombo. A significant negative correlation was seen with the number of cases and school closures (Spearman's r = -0.4732, p <0.0001) and a negative correlation, which was not significant, between the stringency index and case numbers (Spearman's r = -0.3755 p = 0.0587). There was no change in the circulating DENV serotypes with DENV2 remaining the most prevalent serotype by early 2022 (65%), similar to the frequencies observed by end of 2019. The Aedes aegypti premise and container indices showed positive but insignificant correlations with dengue case numbers (Spearman r = 0.8827, p = 0.93). Lockdown measures, especially school closures seemed to have had a significant impact on the number of dengue cases, while the vector indices had a limited effect.

Artificial light at night disrupts species interactions and changes insect communities

Artificial light at night (ALAN) is globally increasing, posing a threat to biodiversity. The impact of nocturnal illumination on individual insects has been relatively well documented. Recent studies show that ALAN also impacts species interactions, including intra-specific communication, trophic interactions and plant-pollinator interactions, with cascading effects in the ecosystem and impacts on ecosystem functioning that extend beyond nocturnal communities and illuminated areas. Reduced population sizes and changes in community composition because of exposure to ALAN have been reported but the understanding of the impacts of ALAN on insect communities is currently limited to few groups and ecosystems. The theoretical framework on how ALAN impacts insect communities and populations is poorly developed, limiting our understanding and the formulation of relevant hypotheses.

Identification of locally isolated entomopathogenic Fusarium species from the soil of Changa Manga Forest, Pakistan and evaluation of their larvicidal efficacy against Aedes aegypti

Dengue fever vectored by the mosquito Aedes aegypti is one of the most rapidly spreading insect-borne diseases. Current reliance of dengue vector control is mostly on chemical insecticides. Growing insecticide resistance in the primary mosquito vector, Aedes aegypti, limits the effectiveness of vector control through chemical insecticides. These chemical insecticides also have negative environmental impacts on animals, plants and human health. Myco-biocontrol agents are naturally occurring organisms and are found to be less damaging to the environment as compared to chemical insecticides. In the present study, entomopathogenic potential of local strains of fungi isolated from soil was assessed for the control of dengue vector. Local fungal isolates presents better alternative to introducing a foreign biocontrol strain, as they may be better adapted to environmental conditions of the area to survive and may have more entomopathogenic efficacy against target organism. Larvicidal efficacy of Fusarium equiseti and Fusarium proliferatum was evaluated against Aedes aegypti. Local strains of F. equiseti (MK371718) and F. proliferatum (MK371715) were isolated from the soil of Changa Manga Forest, Pakistan by using insect bait method. Larvicidal activity of two Fusarium spp. was tested against forth instar larvae of A. aegypti in the laboratory, using concentrations 105, 106, 107 and 108 conidia /ml. LC50 values for F. equiseti after 24h, 48h, 72h and 96h of exposure were recorded as 3.8x 108, 2.9x107, 2.0x107, and 7.1x106 conidia /ml respectively while LC50 values for F. proliferatum were recorded as 1.21x108, 9.6x107, 4.2x107, 2.6x107 conidia /ml respectively after 24h, 48h, 72h and 96h of exposure. The results indicate that among two fungal strains F. equiseti was found to be more effective in terms of its larvicidal activity than F. proliferatum against larvae of A. aegypti.

Highlights of Medical Entomology, 2020

Medical Entomology as a field is inherently global - thriving on international and interdisciplinary collaborations and affected dramatically by arthropod and pathogen invasions and introductions. This past year also will be remembered as the year in which the SARS-CoV-2 COVID-19 pandemic affected every part of our lives and professional activities and impacted (or changed, sometimes in good ways) our ability to collaborate and detect or respond to invasions. This incredible year is the backdrop for the 2020 Highlights in Medical Entomology. This article highlights the broad scope of approaches and disciplines represented in the 2020 published literature, ranging from sensory and chemical ecology, population genetics, impacts of human-mediated environmental change on vector ecology, life history and the evolution of vector behaviors, to the latest developments in vector surveillance and control.

Artificial light at night alters the seasonal responses of biting mosquitoes

Urban light pollution caused by artificial light at night (ALAN) profoundly affects the ecology, behavior, and physiology of plants and animals. Further, this widespread environmental pollutant has the potential to negatively impact human and animal health by changing the seasonal dynamics of disease-transmitting insects. In response to short days, females of the Northern house mosquito enter an overwintering dormancy, or diapause. While in diapause, female mosquitoes divert energy away from reproduction, cease blood-feeding, and no longer transmit disease. We demonstrate that exposure to dim ALAN (~4 lx) causes female mosquitoes to avert diapause and become reproductively active, as these females acquired less fat content, developed larger egg follicles, imbibed vertebrate blood, and produced viable eggs and larvae. Our findings suggest that mosquitoes in highly light-polluted areas such as cities may be actively reproducing and biting later in the season, thereby extending the period of disease risk for urban residents. Our results suggest that ALAN should be considered when modeling mosquito abundance, disease risk, and when deciding how long mosquito surveillance and control should persist in temperate regions.