[Biological threats to global malaria elimination â £ Emergence of invasive vector species].

Driven by international exchanges and climate changes, the invasion and spread of vector Anopheles mosquitoes posed a new challenge to achieving global malaria elimination. Taking the invasion of An. stephensi to exacerbate the malaria epidemic in Africa as an example, this article summarizes the current situation of global Anopheles invasion, and estimates the potential risk of vector Anopheles mosquitoes to unravel the difficulties and challenges in the global malaria elimination program, so as to provide insights into improved early earning and precision control of vector Anopheles mosquito invasion across the world.

Infectivity of Plasmodium parasites to Aedes aegypti and Anopheles stephensi mosquitoes maintained on blood-free meals of SkitoSnack.

BACKGROUND: Aedes and Anopheles mosquitoes are responsible for tremendous global health burdens from their transmission of pathogens causing malaria, lymphatic filariasis, dengue, and yellow fever. Innovative vector control strategies will help to reduce the prevalence of these diseases. Mass rearing of mosquitoes for research and support of these strategies presently depends on meals of vertebrate blood, which is subject to acquisition, handling, and storage issues. Various blood-free replacements have been formulated for these mosquitoes, but none of these replacements are in wide use, and little is known about their potential impact on competence of the mosquitoes for Plasmodium infection. METHODS: Colonies of Aedes aegypti and Anopheles stephensi were continuously maintained on a blood-free replacement (SkitoSnack; SS) or bovine blood (BB) and monitored for engorgement and hatch rates. Infections of Ae. aegypti and An. stephensi were assessed with Plasmodium gallinaceum and P. falciparum, respectively. RESULTS: Replicate colonies of mosquitoes were maintained on BB or SS for 10 generations of Ae. aegypti and more than 63 generations of An. stephensi. The odds of engorgement by SS- relative to BB-maintained mosquitoes were higher for both Ae. aegypti (OR = 2.6, 95% CI 1.3-5.2) and An. stephensi (OR 2.7, 95% CI 1.4-5.5), while lower odds of hatching were found for eggs from the SS-maintained mosquitoes of both species (Ae. aegypti OR = 0.40, 95% CI 0.26-0.62; An. stephensi OR = 0.59, 95% CI 0.36-0.96). Oocyst counts were similar for P. gallinaceum infections of Ae. aegypti mosquitoes maintained on SS or BB (mean ratio = [mean on SS]/[mean on BB] = 1.11, 95% CI 0.85-1.49). Similar oocyst counts were also observed from the P. falciparum infections of SS- or BB-maintained An. stephensi (mean ratio = 0.76, 95% CI 0.44-1.37). The average counts of sporozoites/mosquito showed no evidence of reductions in the SS-maintained relative to BB-maintained mosquitoes of both species. CONCLUSIONS: Aedes aegypti and An. stephensi can be reliably maintained on SS over multiple generations and are as competent for Plasmodium infection as mosquitoes maintained on BB. Use of SS alleviates the need to acquire and preserve blood for mosquito husbandry and may support new initiatives in fundamental and applied research, including novel manipulations of midgut microbiota and factors important to the mosquito life cycle and pathogen susceptibility.

Effects of a blood-free mosquito diet on fitness and gonotrophic cycle parameters of laboratory reared Anopheles gambiae sensu stricto.

BACKGROUND: The current rise of new innovative tools for mosquito control, such as the release of transgenic mosquitoes carrying a dominant lethal gene and Wolbachia-based strategies, necessitates a massive production of mosquitoes in the insectary. However, currently laboratory rearing depends on vertebrate blood for egg production and maintenance. This practice raises ethical concerns, incurs logistical and cost limitations, and entails potential risk associated with pathogen transmission and blood storage. Consequently, an artificial blood-free diet emerges as a desirable alternative to address these challenges. This study aims to evaluate the effects of a previously formulated artificial blood-free diet (herein referred to as BLOODless) on Anopheles gambiae (An. gambiae s.s.; IFAKARA) gonotrophic parameters and fitness compared with bovine blood. METHODS: The study was a laboratory-based comparative evaluation of the fitness, fecundity and fertility of An. gambiae s.s. (IFAKARA) reared on BLOODless versus vertebrate blood from founder generation (F0) to eighth generation (F8). A total of 1000 female mosquitoes were randomly selected from F0, of which 500 mosquitoes were fed with bovine blood (control group) and the other 500 mosquitoes were fed with BLOODless diet (experimental group). The feeding success, number of eggs per female, hatching rate and pupation rate were examined post-feeding. Longevity and wing length were determined as fitness parameters for adult male and female mosquitoes for both populations. RESULTS: While blood-fed and BLOODless-fed mosquitoes showed similar feeding success, 92.3% [95% confidence interval (CI) 89.7-94.9] versus 93.6% (95% CI 90.6-96.6), respectively, significant differences emerged in their reproductive parameters. The mean number of eggs laid per female was significantly higher for blood-fed mosquitoes (P < 0.001) whereas BLOODless-fed mosquitoes had significantly lower hatching rates [odds ratio (OR) 0.17, 95% CI 0.14-0.22, P < 0.001]. Wing length and longevity were similar between both groups. CONCLUSIONS: This study demonstrates the potential of the BLOODless diet as a viable and ethical alternative to vertebrate blood feeding for rearing An. gambiae s.s. This breakthrough paves the way for more efficient and ethical studies aimed at combating malaria and other mosquito-borne diseases.

Non-contact detection of pyrethroids widely used in vector control by Anopheles mosquitoes.

Pyrethroids are the most widely used insecticides to control vector borne diseases including malaria. Physiological resistance mechanisms to these insecticides have been well described, whereas those for behavioral resistance remain overlooked. Field data suggest the presence of spatial sensory detection by Anopheles mosquitoes of the pyrethroid molecules used in insecticide-based control tools, such as long-lasting insecticide nets or insecticide residual spraying. This opens the way to the emergence of a wide range of behavioral adaptations among malaria vectors. However, the spatial sensory detection of these molecules is controversial and needs to be demonstrated. The goal of this study was to behaviorally characterize the non-contact detection of three of the most common pyrethroids used for malaria vector control: permethrin, deltamethrin an ⍺-cypermethrin. To reach this goal, we recorded the behavior (takeoff response) of Anopheles gambiae pyrethroid-sensitive and resistant laboratory strains, as well as field collected mosquitoes from the Gambiae Complex, when exposed to the headspace of bottles containing different doses of the insecticides at 25 and 35°C, in order to represent a range of laboratory and field temperatures. We found the proportion of laboratory susceptible and resistant female mosquitoes that took off was, in all treatments, dose and the temperature dependent. Sensitive mosquitoes were significantly more prone to take off only in the presence of ⍺-cypermethrin, whereas sensitive and resistant mosquitoes showed similar responses to permethrin and deltamethrin. Field-collected mosquitoes of the Gambiae Complex were also responsive to permethrin, independently of the species identity (An. gambiae, An. coluzzii and An. arabiensis) or their genotypes for the kdr mutation, known to confer resistance to pyrethroids. The observed ability of Anopheles spp. mosquitoes to detect insecticides without contact could favor the evolution of behavioral modifications that may allow them to avoid or reduce the adverse effect of insecticides and thus, the development of behavioral resistance.

Livestock keeping, mosquitoes and community viewpoints: a mixed methods assessment of relationships between livestock management, malaria vector biting risk and community perspectives in rural Tanzania.

BACKGROUND: Livestock keeping is one of the potential factors related to malaria transmission. To date, the impact of livestock keeping on malaria transmission remains inconclusive, as some studies suggest a zooprophylactic effect while others indicate a zoopotentiation effect. This study assessed the impact of livestock management on malaria transmission risks in rural Tanzania. Additionally, the study explored the knowledge and perceptions of residents about the relationships between livestock keeping and malaria transmission risks in a selected village. METHODS: In a longitudinal entomological study in Minepa village, South Eastern Tanzania, 40 households were randomly selected (20 with livestock, 20 without). Weekly mosquito collection was performed from January to April 2023. Indoor and outdoor collections used CDC-Light traps, Prokopack aspirators, human-baited double-net traps, and resting buckets. A subsample of mosquitoes was analysed using PCR and ELISA for mosquito species identification and blood meal detection. Livestock's impact on mosquito density was assessed using negative binomial GLMMs. Additionally, in-depth interviews explored community knowledge and perceptions of the relationship between livestock keeping and malaria transmission risks. RESULTS: A total of 48,677 female Anopheles mosquitoes were collected. Out of these, 89% were Anopheles gambiae sensu lato (s.l.) while other species were Anopheles funestus s.l., Anopheles pharoensis, Anopheles coustani, and Anopheles squamosus. The findings revealed a statistically significant increase in the overall number of An. gambiae s.l. outdoors (RR = 1.181, 95%CI 1.050-1.862, p = 0.043). Also, there was an increase of the mean number of An. funestus s.l. mosquitoes collected in households with livestock indoors (RR = 2.866, 95%CI: 1.471-5.582, p = 0.002) and outdoors (RR = 1.579,95%CI 1.080-2.865, p = 0.023). The human blood index of Anopheles arabiensis mosquitoes from houses with livestock was less than those without livestock (OR = 0.149, 95%CI 0.110-0.178, p < 0.001). The majority of participants in the in-depth interviews reported a perceived high density of mosquitoes in houses with livestock compared to houses without livestock. CONCLUSION: Despite the potential for zooprophylaxis, this study indicates a higher malaria transmission risk in livestock-keeping communities. It is crucial to prioritize and implement targeted interventions to control vector populations within these communities. Furthermore, it is important to enhance community education and awareness regarding covariates such as livestock that influence malaria transmission.

Entomological effects of attractive targeted sugar bait station deployment in Western Zambia: vector surveillance findings from a two-arm cluster randomized phase III trial.

BACKGROUND: Attractive targeted sugar bait (ATSB) stations are a novel tool with potential to complement current approaches to malaria vector control. To assess the public health value of ATSB station deployment in areas of high coverage with standard vector control, a two-arm cluster-randomized controlled trial (cRCT) of Sarabi ATSB® stations (Westham Ltd., Hod-Hasharon, Israel) was conducted in Western Province, Zambia, a high-burden location were Anopheles funestus is the dominant vector. The trial included 70 clusters and was designed to measure the effect of ATSBs on case incidence and infection prevalence over two 7-month deployments. Reported here are results of the vector surveillance component of the study, conducted in a subset of 20 clusters and designed to provide entomological context to guide overall interpretation of trial findings. METHODS: Each month, 200 paired indoor-outdoor human landing catch (HLC) and 200 paired light trap (LT) collections were conducted to monitor An. funestus parity, abundance, biting rates, sporozoite prevalence, and entomological inoculation rates (EIR). RESULTS: During the study 20,337 female An. funestus were collected, 11,229 from control and 9,108 from intervention clusters. A subset of 3,131 HLC specimens were assessed for parity: The mean non-parous proportion was 23.0% (95% CI 18.2-28.7%, total n = 1477) in the control and 21.2% (95% CI 18.8-23.9%, total n = 1654) in the intervention arm, an OR = 1.05 (95% CI 0.82-1.34; p = 0.688). A non-significant reduction in LT abundance (RR = 0.65 [95% CI 0.30-1.40, p = 0.267]) was associated with ATSB deployment. HLC rates were highly variable, but model results indicate a similar non-significant trend with a RR = 0.68 (95%CI 0.22-2.00; p = 0.479). There were no effects on sporozoite prevalence or EIR. CONCLUSIONS: Anopheles funestus parity did not differ across study arms, but ATSB deployment was associated with a non-significant 35% reduction in vector LT density, results that are consistent with the epidemiological impact reported elsewhere. Additional research is needed to better understand how to maximize the potential impact of ATSB approaches in Zambia and other contexts. TRIAL REGISTRATION NUMBER: This trial was registered with Clinicaltrials.gov (NCT04800055, 16 March 2021).

Malaria prevalence and transmission in the Zakpota sub-district of central Benin: baseline characteristics for a community randomised trial of a new insecticide for indoor residual spraying.

BACKGROUND: Malaria transmission is known to be perennial and heterogeneous in Benin. Studies assessing local malaria prevalence, transmission levels and vector characteristics are critical for designing, monitoring and evaluating new vector control interventions in community trials. We conducted a study in the Zakpota sub-district of central Benin to collect baseline data on household characteristics, malaria prevalence, vector characteristics and transmission dynamics in preparation for a randomised controlled trial to evaluate the community impact of VECTRON™ T500, a new broflanilide indoor residual spraying (IRS) product. METHODS: A total of 480 children under 5 years of age from the 15 villages of the sub-district were tested for malaria by rapid diagnostic tests (RDTs). Mosquitoes were collected by human landing catches (HLCs), pyrethrum spray catches (PSCs) and Centers for Disease Control and Prevention miniature light traps (CDC-LTs) in selected houses in each village to assess vector density, composition, vector infectivity and prevalence of insecticide resistance markers. Bioassays were performed to detect vector susceptibility to pyrethroids, broflanilide (6 µg/bottle) and clothianidin (90 µg/bottle). RESULTS: A total of 9080 households were enumerated in the 15 study villages. Insecticide-treated net (ITN) usage was > 90%, with 1-2 ITNs owned per household. Houses were constructed mainly with cement (44%) and mud (38%) substrates or a mixture of cement and mud (18%), and 60% of them had open eaves. The overall prevalence of P. falciparum infection was 19% among surveyed children: 20% among females and 18% among males. The haemoglobin rate showed an anaemia (< 11 g/dl) prevalence of 66%. Anopheles coluzzii and An. gambiae sensu stricto (s.s.) were the two vector species present at an overall proportion of 46% versus 54%, respectively. The human biting rate was 2.3 bites per person per night (b/p/n) and biting occurred mostly indoors compared with outdoors (IRR = 0.776; P = 0.001). The overall proportion of outdoor biting was 44% and exceeded indoor biting in three villages. The sporozoite rate was 2% with a combined yearly entomological inoculation rate (EIR) of 16.1 infected bites per person per year (ib/p/y). There was great variability in malaria transmission risk across the villages, with EIR ranging from 0 to 29.3 ib/p/y. The vector population showed a high intensity of resistance to pyrethroids across the study villages but was largely susceptible to broflanilide and clothianidin. CONCLUSIONS: This study found high levels of malaria prevalence, vector density and transmission in the Zakpota sub-district despite the wide use of insecticide-treated nets. The vector population was mostly indoor resting and showed a high intensity of pyrethroid resistance but was generally fully susceptible to broflanilide. These findings demonstrated the suitability of the study area for the assessment of VECTRON™ T500 in a community randomised trial.

Bionomic characterization of Anopheles mosquitoes in the Ethiopian highlands and lowlands.

BACKGROUND: The protective effectiveness of vector control in malaria relies on how the implemented tools overlap with mosquito species-specific compositions and bionomic traits. In Ethiopia, targeted entomological data enabling strategic decision-making are lacking around high-risk migrant worker camps in the lowlands and resident communities in the highlands-resulting in suboptimal malaria control strategies for both populations. This study investigates spatial and temporal mosquito behavior, generating baseline evidence that will improve malaria control for both migrant workers in the lowlands and their home communities in the highlands. METHODS: Hourly Centers for Disease Control and Prevention (CDC) light trap collections were performed indoors and outdoors during the peak (October to December 2022) and minor (March to May 2023) malaria transmission seasons. These seasons coincide with the post-long rain and post-short rain seasons, respectively. Eight resident households were sampled from each of four villages in the highlands and eight households/farm structures on and near farms in four villages in the lowlands. The sampling occurred between 18:00 and 06:00. Spatiotemporal vector behaviors and hourly indoor and outdoor mosquito capture rates, used as a proxy for human biting rates, were calculated for overall catches and for individual species. Adult mosquitoes were identified using morphological keys, and a subset of samples were confirmed to species by sequencing ribosomal DNA internal transcribed spacer region 2 (ITS2) and/or mitochondrial DNA cytochrome c oxidase subunit 1 (Cox1). RESULTS: In the highlands, 4697 Anopheles mosquitoes belonging to 13 morphologically identified species were collected. The predominant species of Anopheles identified in the highlands was An. gambiae sensu lato (s.l.) (n = 1970, 41.9%), followed by An. demeilloni (n = 1133, 24.1%) and An. cinereus (n = 520, 11.0%). In the lowland villages, 3220 mosquitoes belonging to 18 morphological species were collected. Anopheles gambiae s.l. (n = 1190, 36.9%), An. pretoriensis (n = 899, 27.9%), and An. demeilloni (n = 564, 17.5%) were the predominant species. A total of 20 species were identified molecularly, of which three could not be identified to species through comparison with published sequences. In highland villages, the indoor Anopheles mosquito capture rate was much greater than the outdoor rate. This trend reversed in the lowlands, where the rate of outdoor captures was greater than the indoor rate. In both highlands and lowlands, Anopheles mosquitoes showed early biting activities in the evening, which peaked between 18:00 and 21:00, for both indoor and outdoor locations. CONCLUSIONS: The high diversity of Anopheles vectors and their variable behaviors result in a dynamic and resilient transmission system impacting both exposure to infectious bites and intervention effectiveness. This creates gaps in protection allowing malaria transmission to persist. To achieve optimal control, one-size-fits-all strategies must be abandoned, and interventions should be tailored to the diverse spatiotemporal behaviors of different mosquito populations.

Effect of Microsporidia MB infection on the development and fitness of Anopheles arabiensis under different diet regimes.

BACKGROUND: Microsporidia MB (MB) is a naturally occurring symbiont of Anopheles and has recently been identified as having a potential to inhibit the transmission of Plasmodium in mosquitoes. MB intensity is high in mosquito gonads, with no fitness consequences for the mosquito, and is linked to horizontal (sexual) and vertical (transovarial) transmission from one mosquito to another. Maximising MB intensity and transmission is important for maintaining heavily infected mosquito colonies for experiments and ultimately for mosquito releases. We have investigated how diet affects the MB-Anopheles arabiensis symbiosis phenotypes, such as larval development and mortality, adult size and survival, as well as MB intensity in both larvae and adults. METHODS: F1 larvae of G0 females confirmed to be An. arabiensis and infected with MB were either combined (group lines [GLs]) or reared separately (isofemale lines [IMLs]) depending on the specific experiment. Four diet regimes (all mg/larva/day) were tested on F1 GLs: Tetramin 0.07, Tetramin 0.3, Gocat 0.3 and Cerelac 0.3. GLs reared on Tetramin 0.3 mg/larva/day were then fed either a 1% or 6% glucose diet to determine adult survival. Larvae of IMLs were fed Tetramin 0.07 mg and Tetramin 0.3 mg for larval experiments. The mosquitoes in the adult experiments with IMLs were reared on 1% or 6% glucose. RESULTS: Amongst the four larval diet regimes tested on An. arabiensis development in the presence of MB, the fastest larval development highest adult emergence, largest body size of mosquitoes, highest prevalence and highest density of MB occurred in those fed Tetramin 0.3 mg/larva/day. Although adult MB-positive mosquitoes fed on 6% glucose survived longer than MB-negative mosquitoes, there was no such effect for those fed on the 1% glucose diet. Development time, wing length and adult survival were not significantly different between MB-infected and uninfected An. arabiensis fed on the Tetramin 0.07 mg/larva/day diet, demonstrating that the MB-conferred fitness advantage was diet-dependent. CONCLUSIONS: Microsporidia MB does not adversely impact the development and fitness of An. arabiensis, even under limited dietary conditions. The diet regime of Tetramin 0.3 mg/larva/day + 6% glucose for adults is the superior diet for the mass rearing of MB-infected An. arabiensis mosquitoes. These results are important for rearing MB-infected An. arabiensis in the laboratory for experiments and the mass rearing required for field releases.

Deployment of attractive targeted sugar baits in western Zambia: installation, monitoring, removal, and disposal procedures during a Phase III cluster randomized controlled trial.

BACKGROUND: Attractive Targeted Sugar Baits (ATSBs) offer a complementary vector control strategy to interventions targeting blood feeding or larval control by attacking the sugar feeding behaviour of adult mosquitoes using an attract-and-kill approach. Western Zambia was the first location to receive and deploy ATSB Sarabi version 1.2 stations in a Phase III cluster randomized controlled trial. This paper describes ATSB station installation, monitoring, removal, and disposal, quantifies ATSB station coverage, and reports major reasons for ATSB station replacement. METHODS: ATSB stations were deployed during two annual transmission seasons, through scheduled installation and removal campaigns. During deployment, monitoring was conducted per protocol to maintain high coverage of the ATSB stations in good condition. Routine monitoring visits during the trial captured details on ATSB station damage necessitating replacement following pre-defined replacement criteria. Annual cross-sectional household surveys measured ATSB station coverage during peak malaria transmission. RESULTS: A total of 67,945 ATSB stations were installed in Year 1 (41,695 initially installed+ 26,250 installed during monitoring) and 69,494 ATSB stations were installed in Year 2 (41,982 initially installed+ 27,512 installed during monitoring) across 35 intervention clusters to maintain high coverage of two ATSB stations in good condition per eligible household structure. The primary reasons for ATSB station replacement due to damage were holes/tears and presence of mold. Cross-sectional household surveys documented high coverage of ATSB stations across Year 1 and Year 2 with 93.1% of eligible structures having ≥ 2 ATSB stations in any condition. DISCUSSION: ATSB station deployment and monitoring efforts were conducted in the context of a controlled cRCT to assess potential product efficacy. Damage to ATSB stations during deployment required replacement of a subset of stations. High coverage of eligible structures was maintained over the two-year study despite replacement requirements. Additional research is needed to better understand the impact of damage on ATSB station effectiveness under programmatic conditions, including thresholds of threats to physical integrity and biological deterioration on product efficacy. CONCLUSIONS: Optimizing ATSB stations to address causes of damage and conducting implementation research to inform optimal delivery and cost-effective deployment will be important to facilitate scale-up of ATSB interventions.

Diversity and ecological niche model of malaria vector and non-vector mosquito species in Covè, Ouinhi, and Zangnanado, Southern Benin.

The present study aimed to assess mosquito species diversity, distribution, and ecological preferences in the Covè, Ouinhi, and Zangnanado communes, Southern Benin. Such information is critical to understand mosquito bio-ecology and to focus control efforts in high-risk areas for vector-borne diseases. Mosquito collections occurred quarterly in 60 clusters between June 2020 and April 2021, using human landing catches. In addition to the seasonal mosquito abundance, Shannon's diversity, Simpson, and Pielou's equitability indices were also evaluated to assess mosquito diversity. Ecological niche models were developed with MaxEnt using environmental variables to assess species distribution. Overall, mosquito density was higher in the wet season than in the dry season in all communes. A significantly higher Shannon's diversity index was also observed in the wet season than in the dry seasons in all communes (p < 0.05). Habitat suitability of An. gambiae s.s., An. coluzzii, Cx. quinquefasciatus and Ma. africana was highly influenced by slope, isothermality, site aspect, elevation, and precipitation seasonality in both wet and dry seasons. Overall, depending on the season, the ecological preferences of the four main mosquito species were variable across study communes. This emphasizes the impact of environmental conditions on mosquito species distribution. Moreover, mosquito populations were found to be more diverse in the wet season compared to the dry season.

Modelling mosquito population suppression based on competition system with strong and weak Allee effect.

Mosquito-borne diseases are threatening half of the world's population. To prevent the spread of malaria, dengue fever, or other mosquito-borne diseases, a new disease control strategy is to reduce or eradicate the wild mosquito population by releasing sterile mosquitoes. To study the effects of sterile insect technique on mosquito populations, we developed a mathematical model of constant release of sterile Aedes aegypti mosquitoes with strong and weak Allee effect and considered interspecific competition with Anopheles mosquitoes. We calculated multiple release thresholds and investigated the dynamical behavior of this model. In order to get closer to reality, an impulsive differential equation model was also introduced to study mosquito suppression dynamics under the strategy of releasing $ c $ sterile male mosquitoes at each interval time $ T $. Finally, the relationship between the releasing amount or the waiting period and the number of days required to suppress mosquitoes was illustrated by numerical simulations.

Chemical Composition, Repellent, and Oviposition Deterrent Potential of Wild Plant Essential Oils against Three Mosquito Species.

In this study, the chemical composition, repellent, and oviposition deterrent effects of five plant essential oils (EOs) extracted from Lantana camara (Verbenaceae), Schinus terebinthifolia (Anacardiaceae), Callistemon viminalis (Myrtaceae), Helichrysum odoratissimum (Asteraceae), and Hyptis suaveolens (Lamiaceae) were evaluated against Aedes aegypti, Anopheles gambiae, and Culex quinquefasciatus. When tested at 33.3 µg/cm2, L. camara, S. terebinthifolia, C. viminalis, and H. odoratissimum were effective repellents against Ae. aegypti (89%, 91%, 90%, and 51% repellency, respectively), but they were less repellent against An. gambiae (66%, 86%, 59%, and 49% repellency, respectively). Interestingly, L. camara, S. terebinthifolia, C. viminalis, and H. odoratissimum exhibited 100% repellency against Cx. quinquefasciatus at 33.3 µg/cm2. In time-span bioassays performed at 333 µg/cm2, the EO of L. camara exhibited 100% repellence against Ae. aegypti and An. gambiae for up to 15 min and against Cx. quinquefasciatus for 75 min. The oviposition bioassays revealed that L. camara exhibited the highest activity, showing 85%, 59%, and 89% oviposition deterrence against Ae. aegypti, An. gambiae, and Cx. quinquefasciatus, respectively. The major compounds of L. camara, S. terebinthifolia, and C. viminalis were trans-ß-caryophyllene (16.7%), α-pinene (15.5%), and 1,8-cineole (38.1%), respectively. In conclusion, the L. camara and S. terebinthifolia EOs have the potential to be natural mosquito repellents.

First record of Anopheles claviger (Meigen, 1804) (Diptera, Culicidae) in Karelia, Northwestern Russia.

Anopheles claviger (Meigen, 1804) (Diptera, Culicidae) is widespread in the western Palaearctic Region, but it was recorded in Karelia (Russia) for the first time. This record is one of the northernmost ones in the Palaearctic Region and Russia, updates the northern border of the An. claviger range. Mosquitoes were collected from July to September 2023 in the southern Karelia (the village of Gomselga, Kondopoga District, and Petrozavodsk) using Krishtal trap (from human) and Mosquito Magnet® trap (Pioneer design, Octenol as attractant). Seven females of An. claviger were collected in Gomselga; one specimen was sampled from Petrozavodsk City parks. Morphological identification of eight females was verified by COI and ITS2 sequences. Phylogenetic analysis of ITS2 and COI sequences confirmed the collected specimens to An. claviger s. s., clustering in both cases in a strongly supported clade clearly differentiated from the closely related species An. petragnani. The high diversity of An. claviger haplotypes from Karelia is in agreement with data from other geographical regions and shows that the records of this species in Gomselga and Petrozavodsk are not accidental.

Colonization of Anopheles coustani, a neglected malaria vector in Madagascar.

Anopheles coustani has long been recognized as a secondary malaria vector in Africa. It has recently been involved in the transmission of both Plasmodium falciparum and P. vivax in Madagascar. As most secondary malaria vectors, An. coustani mainly bites outdoors, which renders the control of this mosquito species difficult using classical malaria control measures, such as the use of bed nets or indoor residual spraying of insecticides. For a better understanding of the biology and vector competence of a vector species, it is useful to rear the species in the laboratory. The absence of a colony hinders the assessment of the bionomics of a species and the development of adapted control strategies. Here, we report the first successful establishment of an An. coustani colony from mosquitoes collected in Madagascar. We used a forced copulation procedure as this mosquito species will not mate in cages. We describe our mosquito colonization procedure with detailed biological features concerning larval to adult development and survival, recorded over the first six critical generations. The procedure should be easily applicable to An. coustani from different African countries, facilitating local investigation of An. coustani vector competence and insecticide resistance using the colony as a reference.

Title: Colonisation d'Anopheles coustani, vecteur négligé du paludisme à Madagascar. Abstract: Anopheles coustani est reconnu depuis longtemps comme un vecteur secondaire du paludisme en Afrique. Il a récemment été impliqué dans la transmission de Plasmodium falciparum et de P. vivax à Madagascar. Comme la plupart des vecteurs secondaires du paludisme, An. coustani pique principalement à l'extérieur, ce qui rend difficile le contrôle de cette espèce de moustique par les mesures classiques de lutte contre le paludisme telles que l'utilisation de moustiquaires ou la pulvérisation intradomiciliaire d'insecticides à effet rémanent. Pour une meilleure compréhension de la biologie et de la compétence vectorielle d'une espèce vectrice, il est utile d'élever l'espèce en laboratoire. L'absence de colonie gêne l'évaluation de la bionomie d'une espèce et le développement de stratégies de contrôle adaptées. Nous rapportons ici le premier établissement réussi d'une colonie d' An. coustani issue de moustiques collectés à Madagascar. Nous avons utilisé une procédure de copulation forcée car cette espèce de moustique ne s'accouple pas en cage. Nous décrivons notre procédure de colonisation des moustiques avec des caractéristiques biologiques détaillées concernant le développement et la survie des stades larvaires aux adultes, enregistrées au cours des six premières générations critiques. La procédure devrait être facilement applicable aux An. coustani de différents pays africains, facilitant les enquêtes locales sur la compétence vectorielle d'An. coustani et sa résistance aux insecticides, en utilisant une colonie comme référence.

Drivers of autochthonous malaria cases over time: could the Central European present the African future?

BACKGROUND: Results of spatial and temporal comparison of malaria hotspots and coldspots could improve the health measures of malaria control and eradication strategies. The study aimed to reveal the spatially and temporally independent correlations between the potentially most effective background variables and the number of autochthonous malaria cases. METHODS: Relationships between malaria cases and background variables were studied in 2 km × 2 km sized quadrates (10 Central European and 10 African). In addition to the current habitat structure of the African sites, annual precipitation, and annual mean temperature, data of the above parameters detected in the nineteenth and twentieth centuries and currently in the Central European sites were included in the analyses (n = 40). Mann-Whitney tests, Principal Component Analysis, and Generalized Linear Models were used for the examinations. RESULTS: In addition to the apparent significant positive correlation of malaria cases with annual rainfall and mean temperature, several correlations were found for habitat parameters. The cover of marshlands in the 19th-century habitat structure of Central European quadrates was considerably the same as in the recent African ones. The extent of rural residential areas was significantly smaller in the 19th-century habitat structure of Central European quadrats than in present-day African ones. According to the revealed correlations, the surface cover of rural residential areas is the main driver of the number of autochthonous malaria cases that we can directly impact. CONCLUSIONS: The study confirmed with historical comparison that not only the annual rainfall and mean temperature, the cover of marshlands and other habitats with breeding sites, but also the elements of the rural human environment play a significant role in the high number of autochthonous malaria cases, probably through the concentration and enhancing sites for vector mosquitoes. The latter confirms that a rapid urbanization process could reduce malaria cases in the most infected areas of Africa. Until the latter happens, extensive biological control of Anopheles larvae and chemical control (both outdoor and indoor) of their imagoes, further mosquito nets, repellents, and carbon dioxide traps will need to be applied more widely in the most heavily infested areas.

A review of applications and limitations of using aquatic macroinvertebrate predators for biocontrol of the African malaria mosquito, Anopheles gambiae sensu lato.

Macroinvertebrate predators such as backswimmers (Heteroptera: Notonectidae), dragonflies (Odonata: Aeshnidae), and predatory diving beetles (Coleoptera: Dytiscidae) naturally inhabit aquatic ecosystems. Some aquatic ecosystems inhabited by these macroinvertebrate predator taxa equally form malaria vector larval habitats. The presence of these predators in malaria vector larval habitats can negatively impact on development, adult body size, fecundity, and longevity of the malaria vectors, which form important determinants of their fitness and future vectorial capacity. These potential negative impacts caused by aquatic macroinvertebrate predators on malaria vectors warrant their consideration as biocontrol agents in an integrated program to combat malaria. However, the use of these macroinvertebrate predators in malaria biocontrol is currently constrained by technical bottlenecks linked to their generalist predatory tendencies and often long life cycles, demanding complex rearing systems. We reviewed the literature on the use of aquatic macroinvertebrate predators for biocontrol of malaria vectors from the An. gambiae s.l. complex. The available information from laboratory and semi-field studies has shown that aquatic macroinvertebrates have the potential to consume large numbers of mosquito larvae and could thus offer an additional approaches in integrated malaria vector management strategies. The growing number of semi-field structures available in East and West Africa provides an opportunity to conduct ecological experimental studies to reconsider the potential of using aquatic macroinvertebrate predators as a biocontrol tool. To achieve a more sustainable approach to controlling malaria vector populations, additional, non-chemical interventions could provide a more sustainable approach, in comparison with the failing chemical control tools, and should be urgently considered for integration with the current mosquito vector control campaigns.

Structural basis of odor sensing by insect heteromeric odorant receptors.

Most insects, including human-targeting mosquitoes, detect odors through odorant-activated ion channel complexes consisting of a divergent odorant-binding subunit (OR) and a conserved co-receptor subunit (Orco). As a basis for understanding how odorants activate these heteromeric receptors, we report here cryo-electron microscopy structures of two different heteromeric odorant receptor complexes containing ORs from disease-vector mosquitos Aedes aegypti or Anopheles gambiae. These structures reveal an unexpected stoichiometry of one OR to three Orco subunits. Comparison of structures in odorant-bound and unbound states indicates that odorant binding to the sole OR subunit is sufficient to open the channel pore, suggesting a mechanism of OR activation and a conceptual framework for understanding evolution of insect odorant receptor sensitivity.

Eliminating malaria vectors with precision-guided sterile males.

Controlling the principal African malaria vector, the mosquito Anopheles gambiae, is considered essential to curtail malaria transmission. However, existing vector control technologies rely on insecticides, which are becoming increasingly ineffective. Sterile insect technique (SIT) is a powerful suppression approach that has successfully eradicated a number of insect pests, yet the A. gambiae toolkit lacks the requisite technologies for its implementation. SIT relies on iterative mass releases of nonbiting, nondriving, sterile males which seek out and mate with monandrous wild females. Once mated, females are permanently sterilized due to mating-induced refractoriness, which results in population suppression of the subsequent generation. However, sterilization by traditional methods renders males unfit, making the creation of precise genetic sterilization methods imperative. Here, we introduce a vector control technology termed precision-guided sterile insect technique (pgSIT), in A. gambiae for inducible, programmed male sterilization and female elimination for wide-scale use in SIT campaigns. Using a binary CRISPR strategy, we cross separate engineered Cas9 and gRNA strains to disrupt male-fertility and female-essential genes, yielding >99.5% male sterility and >99.9% female lethality in hybrid progeny. We demonstrate that these genetically sterilized males have good longevity, are able to induce sustained population suppression in cage trials, and are predicted to eliminate wild A. gambiae populations using mathematical models, making them ideal candidates for release. This work provides a valuable addition to the malaria genetic biocontrol toolkit, enabling scalable SIT-like confinable, species-specific, and safe suppression in the species.

Rapid entomological assessment in eight high malaria endemic regencies in Papua Province revealed the presence of indoor and outdoor malaria transmissions.

Malaria in eastern Indonesia remains high despite significant reduction and elimination in other parts of the country. A rapid entomological assessment was conducted in eight high malaria endemic regencies of Papua Province, Indonesia, to expedite malaria elimination efforts in this region. This study aims to characterize specific, actionable endpoints toward understanding where and when malaria transmission is happening, where interventions may function best, and identify gaps in protection that result in continued transmission. The entomological assessment included identifying potential vectors through human landing catch (HLC), indoor morning and night resting collections, identification of larval sites through surveillance of water bodies, and vector incrimination toward understanding exposure to malaria transmission. Human landing catches (HLCs) and larval collections identified 10 Anopheles species, namely Anopheles koliensis, Anopheles punctulatus, Anopheles farauti, Anopheles hinesorum, Anopheles longirostris, Anopheles peditaeniatus, Anopheles tesselatus, Anopheles vagus, Anopheles subpictus and Anopheles kochi. The most common and abundant species found overall were An. koliensis and An. punctulatus, while An. farauti was found in large numbers in the coastal areas of Mimika and Sarmi Regencies. Vector incrimination on Anopheles collected from HLCs and night indoor resting demonstrated that An. koliensis and An. punctulatus carried Plasmodium in Keerom, Jayapura, and Sarmi Regencies. Analysis of HLCs for the most common species revealed that the An. koliensis and An. punctulatus, bite indoors and outdoors at equal rates, while An. farauti predominantly bite outdoors. Larval surveillance demonstrated that most water bodies in and surrounding residential areas contained Anopheles larvae. This study demonstrated indoor and outdoor exposure to mosquito bites and gaps in protection, enabling exposure to infectious bites in all regencies. This explains why current malaria control efforts focusing on indoor protection have failed to substantially reduce malaria incidence in the region. Optimization of insecticide-treated bed nets (ITNs), as well as installment of mosquito screens in houses, may further reduce indoor transmission. For outdoor transmission, the use of community-centric approaches to reduce or eliminate larval sources within and surrounding the village through the guidance of locally stationed entomologists, along with Social and Behavior Change mediated health education towards the local adoption of mosquito protection tools during outdoor activities, may reduce malaria transmission.