Search

A vertically transmitted microsporidian, Microsporidia MB, with the ability to disrupt Plasmodium development was reported in Anopheles arabiensis from Kenya, East Africa. To demonstrate its range of incidence, archived DNA samples from 7575 Anopheles mosquitoes collected from Ghana were screened. MB prevalence was observed at 1.8%. An. gambiae s.s constituted 87% of positive mosquitoes while the remaining were from An. coluzzii. Both sibling species had similar positivity rates (24% and 19%; p = 0.42) despite the significantly higher number of An. gambiae s.s analysed (An. gambiae s.s = 487; An. coluzzii = 94; p = 0.0005). The microsporidian was also more prevalent in emerged adults from field-collected larvae than field-caught adults (p Microsporidia MB in Anopheles mosquitoes in West Africa. It indicates possible widespread among malaria vector species and warrants investigations into the symbiont’s diversity across sub-Saharan Africa.

A vertically transmitted microsporidian, Microsporidia MB, with the ability to disrupt Plasmodium development was reported in Anopheles arabiensis from Kenya, East Africa. To demonstrate its range of incidence, archived DNA samples from 7575 Anopheles mosquitoes collected from Ghana were screened. MB prevalence was observed at 1.8%. An. gambiae s.s constituted 87% of positive mosquitoes while the remaining were from An. coluzzii. Both sibling species had similar positivity rates (24% and 19%; p= 0.42) despite the significantly higher number of An. gambiae s.s analysed (An. gambiae s.s= 487; An. coluzzii= 94; p= 0.0005). The microsporidian was also more prevalent in field-collected larvae than adults (p< 0.0001) suggestive of an efficient vertical transmission and/or horizontal transfer among larvae. This is the first report of Microsporidia MB in Anopheles mosquitoes in West Africa. It indicates possible widespread among malaria vector species and warrants investigations into the symbiont’s diversity across the sub-Saharan Africa.

In the past decade, there has been increasing interest in mosquito microbiome research, leading to large amounts of data on different mosquito species, with various underlying physiological characteristics, and from diverse geographical locations. However, guidelines and standardized methods for conducting mosquito microbiome research are lacking. To streamline methods in mosquito microbiome research and optimize data quality, reproducibility, and comparability, as well as facilitate data curation in a centralized location, we are establishing the Mosquito Microbiome Consortium, a collaborative initiative for the advancement of mosquito microbiome research. Our overall goal is to collectively work on unraveling the role of the mosquito microbiome in mosquito biology, while critically evaluating its potential for mosquito-borne disease control. This perspective serves to introduce the consortium and invite broader participation. It highlights the issues we view as most pressing to the community and proposes guidelines for conducting mosquito microbiome research. We focus on four broad areas in this piece: (1) sampling/experimental design for field, semi-field, or laboratory studies; (2) metadata collection; (3) sample processing, sequencing, and use of appropriate controls; and (4) data handling and analysis. We finally summarize current challenges and highlight future directions in mosquito microbiome research. We hope that this piece will spark discussions around this area of disease vector biology, as well as encourage careful considerations in the design and implementation of mosquito microbiome research. Video Abstract Supplementary Information The online version contains supplementary material available at 10.1186/s40168-020-00987-7.

Domesticating Zika virus Why hasn't Zika virus (ZIKV) disease caused as much devastation in Africa, its continent of origin, as it has in the Americas? Outside of Africa, this flavivirus is transmitted by a ubiquitous mosquito subspecies, Aedes aegypti aegypti , which emerged from the African forerunner subspecies A. aegypti formosus and acquired a preference for human blood and a peridomestic lifestyle. Now, this subspecies colonizes many intertropical cities, aided by climate change and human trash. Aubry et al. tested 14 laboratory mosquito colonies for their relative susceptibility to ZIKV. Quantitative trait locus mapping showed differences on chromosome 2 between mosquitoes from Gabon and Guadeloupe. Mouse infection experiments revealed that African mosquitoes transmitted a smaller virus inoculum than the South American insects. Increased susceptibility coupled with the ability of A. aegypti aegypti to breed in any discarded object containing water has amplified the problematic nature of this virus as it has circumnavigated the world. Science , this issue p. 991

Some bacteria species found in the mosquito midgut have demonstrated their role in interrupting the development of Plasmodium within the midgut of the Anopheles mosquito and have been identified as potential candidates for novel bacteria-mediated disease control. However, to use these bacteria successfully in biocontrol mechanisms their effect on the fitness of the vector into which they have been introduced has to be evaluated. This study investigated the effect of two such bacteria candidates, Enterobacter cloacae and Serratia marcescens, on Anopheles gambiae s.l. fitness. Pupae and larvae of Anopheles gambiae s.l. mosquitoes were collected by dipping method and reared to adults. The effect of these bacteria on mosquito fitness was assessed by reintroducing isolates of each bacteria separately into antibiotic-treated female adult mosquitoes through sugar meal. Wild type (non-antibiotic-treated) mosquitoes and those antibiotic-treated with no bacteria reintroduction were used as controls. The mosquitoes were monitored on longevity/survival, fecundity, hatch rate, and larval survival. The antibiotic-treated adult mosquitoes had reduced life span with median survival of 14 days while the bacteria-reintroduced groups and the wild type survived to day 22 (p< 0.0001). Treatment with Enterobacter and Serratia did not affect the average egg deposition (p>0.05) but they affected hatch rates positively (p = 0.008). There was, however, some evidence that suggests Enterobacter could have a positive effect on larval development (p < 0.0001). With no observed negative effect on survival/longevity of Anopheles gambiae, introducing E. cloacae and S. marcescens in future bacteria-associated control strategies is unlikely to result in mosquitoes that will be outlived by the wild population. This, however, requires evaluations under field conditions.

Some bacteria species found in the mosquito midgut have demonstrated their role in interrupting the development of Plasmodium within the midgut of the Anopheles mosquito and have been identified as potential candidates for novel bacteria-mediated disease control. However, to use these bacteria successfully in biocontrol mechanisms their effect on the fitness of the vector into which they have been introduced has to be evaluated. This study investigated the effect of two such bacteria candidates, Enterobacter cloacae and Serratia marcescens, on Anopheles gambiae s.l. fitness. Pupae and larvae of Anopheles gambiae s.l. mosquitoes were collected by dipping method and reared to adults. The effect of these bacteria on mosquito fitness was assessed by reintroducing isolates of each bacteria separately into antibiotic-treated female adult mosquitoes through sugar meal. Wild type (non-antibiotic-treated) mosquitoes and those antibiotic-treated with no bacteria reintroduction were used as controls. The mosquitoes were monitored on longevity/survival, fecundity, hatch rate, and larval survival. The antibiotic-treated adult mosquitoes had reduced life span with median survival of 14 days while the bacteria-reintroduced groups and the wild type survived to day 22 (p< 0.0001). Treatment with Enterobacter and Serratia did not affect the average egg deposition (p>0.05) but they affected hatch rates positively (p = 0.008). There was, however, some evidence that suggests Enterobacter could have a positive effect on larval development (p < 0.0001). With no observed negative effect on survival/longevity of Anopheles gambiae, introducing E. cloacae and S. marcescens in future bacteria-associated control strategies is unlikely to result in mosquitoes that will be outlived by the wild population. This, however, requires evaluations under field conditions.

Background The gut microbiota is known to play a role in a mosquito vector’s life history, a subject of increasing research. Laboratory experiments are essential for such studies and require laboratory colonies. In this study, the conservation of field-obtained midgut microbiota was evaluated in laboratory-reared Anopheles gambiae (s.l.) mosquitoes continuously hatched in water from field breeding habitats. Methods Pupae and late instars were obtained from the field and reared, and the emerged adults were blood-fed. The eggs obtained from them were hatched in either water from the field or in dechlorinated tap water. The mosquito colonies were maintained for 10 generations. Midguts of female adults from unfed F0 (emerging from field-caught pupae and larvae), F5 and F10 were dissected out and genomic DNA was extracted for 16S metagenomic sequencing. The sequences were compared to investigate the diversity and bacterial compositional differences using ANCOM and correlation clustering methods. Results Less than 10% of the bacterial families identified had differential relative abundances between generational groups and accounted for 46% of the variation observed. Although diversity reduced in F10 mosquitoes during laboratory colonization (Shannon-Weaver; P-value < 0.05), 50% of bacterial genera were conserved in those bred continuously in field-water compared to 38% in those bred in dechlorinated tap water. Conclusions To our knowledge, this study is the first report on the assessment of gut bacterial community of mosquitoes during laboratory colonization and recommends the use of water from the natural breeding habitats if they are intended for microbiota research. Electronic supplementary material The online version of this article (10.1186/s13071-019-3287-0) contains supplementary material, which is available to authorized users.

Symbiotic bacteria can have important implications in the development and competence of disease vectors. In Anopheles mosquitoes, the composition of the midgut microbiota is largely influenced by the larval breeding site, but the exact factors shaping this composition are currently unknown. Here, we examined whether the proximity to urban areas and seasons have an impact on the midgut microbial community of the two major malaria vectors in Africa, An. coluzzii and An. gambiae. Larvae and pupae were collected from selected habitats in two districts of Ghana during the dry and rainy season periods. The midgut microbiota of adults that emerged from these collections was determined by 454-pyrosequencing of the 16S ribosomal DNA. We show that in both mosquito species, Shewanellaceae constituted on average of 54% and 73% of the midgut microbiota from each site in the dry and rainy season, respectively. Enterobacteriaceae was found in comparatively low abundance below 1% in 22/30 samples in the dry season, and in 25/38 samples in the rainy season. Our data indicate that seasonality and locality significantly affect both the diversity of microbiota and the relative abundance of bacterial families with a positive impact of dry season and peri-urban settings.

The immobilisation of mosquitoes for injection experiments is a requirement that must be achieved for the necessary time duration to complete the process. Unfortunately, the use of cold anaesthesia in hot tropical countries is not very effective and the use of CO2 anaesthesia requires continuous exposure, which can be harmful to the experimenter. To circumvent this problem we evaluated the use of triethylamine (FlyNap) in the anaesthesia of Anopheles gambiae mosquitoes. FlyNap has been used widely in Drosophila studies, and is known to irreversibly anaesthetise mosquitoes. Very small volumes of the original FlyNap as well as different dilutions using absolute ethanol were evaluated to determine the dosage that will effectively anesthetise Anopheles gambiae female mosquitoes for the necessary duration. The results showed that the 1/10 (FlyNap/absolute ethanol) dilution worked well and could be used for the anaesthesia. Injecting live adults mosquitoes for scientific experiments is a delicate process that requires immobilising them for the required period of time. The immobilisation can be done using two main methods; chilling using cold anaesthesia (Garver & Dimopoulos 2007) or by chemical anaesthesia using CO2 (Lamacchia et al. 2013). In tropical climates cold anaesthesia is not very effective, and some mosquitoes can withstand some degree of chilling and hence may not be immobilised for long. Chemical anaesthesia, such as CO2 on the other hand, can result in the death of mosquitoes, and may be harmful to humans. A chemical anaesthesia commonly used is triethylamine. It is safe and poses no harmful effects to humans (Budavari 1989). Triethylamine formulated as FlyNap® (Carolina Biological Supply Co., NC, U.S.A.) is commonly available for anaesthetic purposes for insects. FlyNap is a mixture of 50 % triethylamine, 25 % ethanol and 25 % fragrance. It is 100 % volatile, water-soluble and can be stored in a cool, well-ventilated place. When exposed to FlyNap, insects are quickly incapacitated but remain alive and are unable to fly for several hours (Kramer et al. 1990). However, when in high doses, exposure causes death of the insect. It has been widely used in Drosophila anaesthesia (Paternostro et al. 2001; Babcock et al. 2008), and only used in lethal doses to kill mosquitoes (O’Guinn & Turell 2002; Goodman et al. 2003; Chen & Hillyer 2013). Our attempts to immobilise adult Anopheles gambiae mosquitoes using cold anaesthesia for injection experiments have proven unsuccessful, primarily due to the inability to immobilise mosquitoes long enough to complete the procedure. To circumvent this problem, this study aimed at evaluating the use of FlyNap and the dosage that will effectively anaesthetise An. gambiae long enough for experimental assays, and also result in high mosquito recovery rates. The experiment was conducted with 3and 5day-old Kisumu strain female An. gambiae mosquitoes. The mosquitoes were fed ad libitum on 10 % sucrose solution, following emergence. For each experiment, 10 mosquitoes were placed in a plastic cup and exposed to one of the following concentrations of FlyNap: 1 μl and 2 μl of stock, as well as 10 μl solutions of 1/10, 1/100, 1/1000 dilutions of FlyNap. The dilutions were prepared with absolute ethanol. The FlyNap to be tested was aliquoted onto small cotton balls and placed in the cups with the mosquitoes. To evaluate the additional effect of the ethanol in anaesthetising the mosquitoes, a control experiment using 10 μl absolute ethanol only was included for the 3and 5-day-old mosquito groups. Each cup was turned upside down to ensure that the fumes from the FlyNap did not escape and could effectively knock down the mosquitoes. The time taken for the first mosquito to be knocked down was recorded for each experiment, and the number of mosquitoes knocked down was recorded at 10-min intervals. After all mosquitoes were knocked down, they were transferred to new cups. The time taken for the first mosquito to revive was noted, and the number of revived mosquitoes was subsequently recorded at 30-min intervals. All experiments were replicated three times to determine the average time of knock *Author for correspondence. E-mail: ddesouza@noguchi.ug.edu.gh