Role of fish as predators of mosquito larvae on the floodplain of the Gambia River

Distinct developmental patterns in Anopheles stephensi organ systems

Anatomical profiles of insects inform vector biology, comparative development and evolutionary studies with applications in forensics, agriculture and disease control. This study presents a comprehensive, high-resolution developmental profile of Anopheles stephensi, encompassing larval, pupal, and adult stages, obtained through microCT scanning. The results indicate in situ anatomical changes in most organ systems, including the central nervous system, eyes, musculature, alimentary canal, salivary glands, and ovaries, among other organ systems, except for the developing heart. We find significant differences in the mosquito gut, body-wall, and flight muscle development during metamorphosis from other dipterans like Drosophila. Specifically, indirect flight muscle specification and growth can be traced back at least to the 4th instar A. stephensi larvae, as opposed to post-puparial development in other Dipterans like Drosophila and Calliphora. Further, while Drosophila larval body-wall muscles and gut undergo histolysis, changes to these organs during mosquito metamorphosis are less pronounced. These observations, and raw data therein may serve as a reference for studies on the development and the genetics of mosquitoes. Overall, the detailed developmental profile of A. stephensi presented here illuminates the unique anatomy and developmental processes of Culicidae, with important implications for vector biology, disease control, and comparative evolutionary studies.

Effect of predators on Anopheles arabiensis and Anopheles funestus larval survivorship in Homa Bay County Western Kenya

BACKGROUND

The rise of insecticide resistance against malaria vectors in sub-Saharan Africa has resulted in the need to consider other methods of vector control. The potential use of biological methods, including larvivorous fish, Bacillus thuringiensis israelensis (Bti) and plant shading, is sustainable and environmentally friendly options. This study examined the survivorship of Anopheles arabiensis and Anopheles funestus larvae and habitat productivity in four permanent habitat types in Homa Bay county, western Kenya.

METHODS

Predator densities were studied in a laboratory setup while habitat productivity and larval survivorship was studied in field setup.

RESULTS

Fish were observed as the most efficient predator (75.8% larval reduction rate) followed by water boatman (69%), and dragonfly nymph (69.5%) in predation rates. Lower predation rates were observed in backswimmers (31%), water beetles (14.9%), water spiders (12.2%), mayflies (7.3%), and tadpoles (6.9%). Increase in predator density in the field setup resulted in decreased Culex larval density. Larval and pupa age-specific distribution was determined and their survivorship curves constructed. Combined larvae (Stage I-IV) to pupa mortality was over 97% for An. arabiensis and 100% for An. funestus. The highest larval stage survival rate was from larval stages I to II and the lowest from larval stage IV to pupa. Stage-specific life tables indicated high mortality rates at every developmental stage, especially at the larval stage II and III.

CONCLUSION

Determination of the efficiency of various larval predators and habitat productivity will help with the correct identification of productive habitats and selection of complementary vector control methods through environmental management and/or predator introduction (for instance fish) in the habitats.

Comparative Morphology of the Digestive Tract of African Bush Fish (Ctenopoma acutirostre) and Paradise Fish (Macropodus opercularis) Inhabiting Asian and African Freshwaters

Anabantidae is a large and diverse group of fish cultured both under aquaculture conditions and as a hobby. These fish share a common structural feature in the form of an additional respiratory organ. Despite the enormous availability of these fish worldwide, little is known about their feeding preferences in husbandry and their influence on homeostasis under both industrial and domestic conditions. This study describes, for the first time, the structure of the digestive tracts of two Anabantoidei fishes: African bush fish (Ctenopoma acutirostre) and paradise fish (Macropodus opercularis). The overall structure of the digestive tract and its histological structure were analyzed and compared in both fish species. Physiological predispositions indicated a predominance of omnivorous fish traits in M. opercularis in contrast to C. acutirostre, which has several morphological traits indicating greater adaptation to carnivory, particularly ichthyophagy. The results obtained will allow further research to be conducted in the future to optimize the nutrition and feeding of these fish and to develop appropriate dietary recommendations.

Malaria Risk Drivers in the Brazilian Amazon: Land Use-Land Cover Interactions and Biological Diversity

Malaria is a prevalent disease in several tropical and subtropical regions, including Brazil, where it remains a significant public health concern. Even though there have been substantial efforts to decrease the number of cases, the reoccurrence of epidemics in regions that have been free of cases for many years presents a significant challenge. Due to the multifaceted factors that influence the spread of malaria, influencing malaria risk factors were analyzed through regional outbreak cluster analysis and spatio-temporal models in the Brazilian Amazon, incorporating climate, land use/cover interactions, species richness, and number of endemic birds and amphibians. Results showed that high amphibian and bird richness and endemism correlated with a reduction in malaria risk. The presence of forest had a risk-increasing effect, but it depended on its juxtaposition with anthropic land uses. Biodiversity and landscape composition, rather than forest formation presence alone, modulated malaria risk in the period. Areas with low endemic species diversity and high human activity, predominantly anthropogenic landscapes, posed high malaria risk. This study underscores the importance of considering the broader ecological context in malaria control efforts.

Mosquito-Borne Diseases and Their Control Strategies: An Overview Focused on Green Synthesized Plant-Based Metallic Nanoparticles

Mosquitoes act as vectors of pathogens that cause most life-threatening diseases, such as malaria, Dengue, Chikungunya, Yellow fever, Zika, West Nile, Lymphatic filariasis, etc. To reduce the transmission of these mosquito-borne diseases in humans, several chemical, biological, mechanical, and pharmaceutical methods of control are used. However, these different strategies are facing important and timely challenges that include the rapid spread of highly invasive mosquitoes worldwide, the development of resistance in several mosquito species, and the recent outbreaks of novel arthropod-borne viruses (e.g., Dengue, Rift Valley fever, tick-borne encephalitis, West Nile, yellow fever, etc.). Therefore, the development of novel and effective methods of control is urgently needed to manage mosquito vectors. Adapting the principles of nanobiotechnology to mosquito vector control is one of the current approaches. As a single-step, eco-friendly, and biodegradable method that does not require the use of toxic chemicals, the green synthesis of nanoparticles using active toxic agents from plant extracts available since ancient times exhibits antagonistic responses and broad-spectrum target-specific activities against different species of vector mosquitoes. In this article, the current state of knowledge on the different mosquito control strategies in general, and on repellent and mosquitocidal plant-mediated synthesis of nanoparticles in particular, has been reviewed. By doing so, this review may open new doors for research on mosquito-borne diseases.

Perspectives of vector management in the control and elimination of vector-borne zoonoses

The complex transmission profiles of vector-borne zoonoses (VZB) and vector-borne infections with animal reservoirs (VBIAR) complicate efforts to break the transmission circuit of these infections. To control and eliminate VZB and VBIAR, insecticide application may not be conducted easily in all circumstances, particularly for infections with sylvatic transmission cycle. As a result, alternative approaches have been considered in the vector management against these infections. In this review, we highlighted differences among the environmental, chemical, and biological control approaches in vector management, from the perspectives of VZB and VBIAR. Concerns and knowledge gaps pertaining to the available control approaches were discussed to better understand the prospects of integrating these vector control approaches to synergistically break the transmission of VZB and VBIAR in humans, in line with the integrated vector management (IVM) developed by the World Health Organization (WHO) since 2004.

ٍSome biologically active microorganisms have the potential to suppress mosquito larvae (Culex pipiens, Diptera: Culicidae)

Malaria is a disease caused by protozoan species of the genus Plasmodium. It is widespread and becoming a challenge in several African countries in the tropical and subtropical regions. In 2010, a report was published showing that over 1.2 million death cases were occurred globally due to malaria in just one year. The transmission of the disease from one person to another occurs via the bite of the Anopheles female. It is known that Plasmodium ovale, P. vivax, P. malariae, P. falciparum, and P. knowlesi are the highly infective malaria species. The problem of this disease is the absence of any effective medical treatment or vaccine, making the mosquito control is the only feasible way for disease prevention. Pesticides are currently the most widely used method for mosquito control, despite its well-known negative effects, including health hazards on human, the increasing insecticidal resistance, and the negative impact on the environment and beneficial organisms. Biological control (also called: biocontrol) of insects has been a promising method to overcome the negative effects of using chemical insecticides, as it depends on just using the natural enemies of pests to either minimize their populations or eradicate them. This article provides an overview of the recent and effective biological means to control malaria, such as bacteria, fungi, viruses, larvivorous fish, toxorhynchites larva and nematodes. In addition, the importance, advantages, and disadvantages of the biocontrol methods will be discussed in comparison with the traditionally used chemical methods of malaria control with special reference to nanotechnology as a novel method for insects’ control.

Dogs as Sentinels for Flavivirus Exposure in Urban, Peri-Urban and Rural Hanoi, Vietnam

Diseases caused by flaviviruses, including dengue fever and Japanese encephalitis, are major health problems in Vietnam. This cross-sectional study explored the feasibility of domestic dogs as sentinels to better understand risks of mosquito-borne diseases in Hanoi city. A total of 475 dogs serum samples from 221 households in six districts of Hanoi were analyzed by a competitive enzyme-linked immunosorbent assay (cELISA) for antibodies to the pr-E protein of West Nile virus and other flaviviruses due to cross-reactivity. The overall flavivirus seroprevalence in the dog population was 70.7% (95% CI = 66.4–74.8%). At the animal level, significant associations between seropositive dogs and district location, age, breed and keeping practice were determined. At the household level, the major risk factors were rural and peri-urban locations, presence of pigs, coil burning and households without mosquito-borne disease experience (p < 0.05). Mosquito control by using larvicides or electric traps could lower seropositivity, but other measures did not contribute to significant risk mitigation of flavivirus exposure in dogs. These results will support better control of mosquito-borne diseases in Hanoi, and they indicate that dogs can be used as sentinels for flavivirus exposure.

Biological and Chemical Control of Mosquito Population by Optimal Control Approach

This paper focuses on the design and analysis of short-term control intervention measures seeking to suppress local populations of Aedes aegypti mosquitoes, the major transmitters of dengue and other vector-borne infections. Besides traditional measures involving the spraying of larvicides and/or insecticides, we include biological control based on the deliberate introduction of predacious species feeding on the aquatic stages of mosquitoes. From the methodological standpoint, our study relies on application of the optimal control modeling framework in combination with the cost-effectiveness analysis. This approach not only enables the design of optimal strategies for external control intervention but also allows for assessment of their performance in terms of the cost-benefit relationship. By examining numerous scenarios derived from combinations of chemical and biological control measures, we try to find out whether the presence of predacious species at the mosquito breeding sites may (partially) replace the common practices of larvicide/insecticide spraying and thus reduce their negative impact on non-target organisms. As a result, we identify two strategies exhibiting the best metrics of cost-effectiveness and provide some useful insights for their possible implementation in practical settings.

Antipredatory Responses of Mosquito Pupae to Non-Lethal Predation Threat-Behavioral Plasticity Across Life-History Stages

Antipredatory behavioral responses tend to be energetically expensive, and prey species thus need to resolve trade-offs between these behaviors and other activities such as foraging and mating. While these trade-offs have been well-studied across taxa, less is known about how costs and benefits vary in different life-history contexts, and associated consequences. To address this question, we compared responses of the yellow fever mosquito (Aedes aegypti [Diptera: Culicidae]) to predation threat from guppy (Poecilia reticulata [Cyprinodontiformes: Poeciliidae]) across two life-history stages-larvae (data from previous study) and pupae (from this study). Pupae are motile but do not feed and are comparable to larvae in terms of behavior. To understand how physiological costs affect the threat sensitivity of pupae, we used sex (with size as a covariate) as a proxy for stored energy reserves, and quantified movement and space use patterns of male (small-sized) and female (large-sized) pupae when exposed to predation threat. We found that pupae did not alter movement when exposed to predator cues but instead altered spatial use by spending more time at the bottom of the water column. We found no effect of pupa sex (or size) on the behavioral responses we measured. We conclude that pupa behavior, both antipredatory and otherwise, is primarily targeted at minimizing energy expenditure, as compared with larval behavior, which appears to balance energy expenditure between the opposing pressures of foraging and of avoiding predation. We suggest that antipredatory defenses in metamorphosing prey are modulated by varying energetic trade-offs associated with different life-history stages.

Mosquito-Borne Diseases Emergence/Resurgence and How to Effectively Control It Biologically

Deadly pathogens and parasites are transmitted by vectors and the mosquito is considered the most threatening vector in public health, transmitting these pathogens to humans and animals. We are currently witnessing the emergence/resurgence in new regions/populations of the most important mosquito-borne diseases, such as arboviruses and malaria. This resurgence may be the consequence of numerous complex parameters, but the major cause remains the mismanagement of insecticide use and the emergence of resistance. Biological control programmes have rendered promising results but several highly effective techniques, such as genetic manipulation, remain insufficiently considered as a control mechanism. Currently, new strategies based on attractive toxic sugar baits and new agents, such as Wolbachia and Asaia, are being intensively studied for potential use as alternatives to chemicals. Research into new insecticides, Insect Growth Regulators, and repellent compounds is pressing, and the improvement of biological strategies may provide key solutions to prevent outbreaks, decrease the danger to at-risk populations, and mitigate resistance.

Effects of the removal or reduction in density of the malaria mosquito, Anopheles gambiae s.l., on interacting predators and competitors in local ecosystems

New genetic control methods for mosquitoes may reduce vector species without direct effects on other species or the physical environment common with insecticides or drainage. Effects on predators and competitors could, however, be a concern as Anopheles gambiae s.l. is preyed upon in all life stages. We overview the literature and assess the strength of the ecological interactions identified. Most predators identified consume many other insect species and there is no evidence that any species preys exclusively on any anopheline mosquito. There is one predatory species with a specialisation on blood-fed mosquitoes including An. gambiae s.l.. Evarcha culicivora is a jumping spider, known as the vampire spider, found around Lake Victoria. There is no evidence that these salticids require Anopheles mosquitoes and will readily consume blood-fed Culex. Interspecific competition studies focus on other mosquitoes of larval habitats. Many of these take place in artificial cosms and give contrasting results to semi-field studies. This may limit their extrapolation regarding the potential impact of reduced An. gambiae numbers. Previous mosquito control interventions are informative and identify competitive release and niche opportunism; so while the identity and relative abundance of the species present may change, the biomass available to predators may not.

Presence of a predator image in potential breeding sites and oviposition responses of a dengue vector

In dengue vector control, attempts to minimize or replace the use of pesticides have mostly involved use of predators, but success has been severely impeded by difficulties associated with financial and environmental costs, predator mass production, and persistence in target habitats. Visual deterrents have been used successfully to control animal pests, in some cases in an effort to replace pesticide use. Despite evidence that visual signals are crucial in site choice for egg deposition by dengue vectors, and that female mosquitoes respond to artificial predation, the role of predator intimidation as it affects the oviposition behavior of dengue vectors remains largely unexplored. Here, we examined the oviposition responses of Aedes aegypti exposed to various mosquito predator pictures. Gravid females were presented with equal opportunities to oviposit in two cups with predator images [Toxorhynchites splendens-TXI, Goldfish (Carassius auratus)-small (SFI) and large (LFI) and Tx. splendens+Goldfish-TXFI] and two others without pictures. Differences in egg deposition were examined between sites with and without these images. When given a chance to oviposit in cups with and without TXI, Ae. aegypti females were similarly attracted to both sites. When provided an opportunity to oviposit in cups displaying pictures of fish (SFI or LFI) and blank cups, egg deposition rates were much lower in the fish picture sites. Females showed a preference for blank cups over TXFI for egg deposition. They also equally avoided cups with pictures of fish, regardless of the size of the picture. Our results indicate that the presence of images of goldfish and their association with Tx. larvae significantly reduced egg deposition by Ae. aegypti, and this was not the case with the predatory larvae alone. The observations that the images of natural predators can repel gravid females of a dengue vector provide novel possibilities to develop effective and inexpensive alternative tools to harmful insecticides.

Deforestation and vector-borne disease: Forest conversion favors important mosquito vectors of human pathogens

The global burden of vector-borne diseases accounts for more than 17% of infectious diseases in humans. Rapid global expansion of previously obscure pathogens, such as Zika and chikungunya viruses in recent years highlights the importance of understanding how anthropogenic changes influence emergence and spillover of vector-borne diseases. Deforestation has been identified as one anthropogenic change that influences vector-borne disease prevalence, although contrasting pictures of the effects of deforestation on vector-borne disease transmission have been reported. These conflicting findings are likely attributable to the inherent complexity of vector-borne disease systems, which involve diverse groups of vectors, hosts and pathogens, depending on geography. The current study represents a quantitative exploration of the link between deforestation and mosquitoes, the most important common constituents of vector-borne disease systems. Analysis of data compiled from published field studies for 87 mosquito species from 12 countries revealed that about half of the species (52.9%) were associated with deforested habitats. Of these species that are favored by deforestation, a much larger percentage (56.5%) are confirmed vectors of human pathogens, compared to those negatively impacted by deforestation (27.5%). Moreover, species that serve as vectors of multiple human pathogens were all favored by deforestation, including Anopheles bancroftii, Anopheles darlingi, Anopheles farauti, Anopheles funestus s.l., Anopheles gambiae s.l., Anopheles subpictus, Aedes aegypti, Aedes vigilax, Culex annulirostris, and Culex quinquefasciatus. Our quantitative analysis of vector and non-vector species, demonstrates that the net effect of deforestation favors mosquitoes that serve as vectors of human disease, while the obverse holds true for non-vectors species. These results begin to unify our understanding of the relationship between deforestation and vector mosquitoes, an important step in quantifying how land use change, specifically deforestation, affects human risk of vector-borne disease.

Biological Control of Mosquito Vectors: Past, Present, and Future

Mosquitoes represent the major arthropod vectors of human disease worldwide transmitting malaria, lymphatic filariasis, and arboviruses such as dengue virus and Zika virus. Unfortunately, no treatment (in the form of vaccines or drugs) is available for most of these diseases and vector control is still the main form of prevention. The limitations of traditional insecticide-based strategies, particularly the development of insecticide resistance, have resulted in significant efforts to develop alternative eco-friendly methods. Biocontrol strategies aim to be sustainable and target a range of different mosquito species to reduce the current reliance on insecticide-based mosquito control. In this review, we outline non-insecticide based strategies that have been implemented or are currently being tested. We also highlight the use of mosquito behavioural knowledge that can be exploited for control strategies.

Multipurpose effectiveness of Couroupita guianensis-synthesized gold nanoparticles: high antiplasmodial potential, field efficacy against malaria vectors and synergy with Aplocheilus lineatus predators

Mosquito-borne diseases represent a deadly threat for millions of people worldwide. According to recent estimates, about 3.2 billion people, almost half of the world's population, are at risk of malaria. Malaria control is particularly challenging due to a growing number of chloroquine-resistant Plasmodium and pesticide-resistant Anopheles vectors. Newer and safer control tools are required. In this research, gold nanoparticles (AuNPs) were biosynthesized using a cheap flower extract of Couroupita guianensis as reducing and stabilizing agent. The biofabrication of AuNP was confirmed by UV-vis spectrophotometry, Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), zeta potential, and particle size analysis. AuNP showed different shapes including spheres, ovals, and triangles. AuNPs were crystalline in nature with face-centered cubic geometry; mean size was 29.2-43.8 nm. In laboratory conditions, AuNPs were toxic against Anopheles stephensi larvae, pupae, and adults. LC50 was 17.36 ppm (larva I), 19.79 ppm (larva II), 21.69 ppm (larva III), 24.57 ppm (larva IV), 28.78 ppm (pupa), and 11.23 ppm (adult). In the field, a single treatment with C. guianensis flower extract and AuNP (10 × LC50) led to complete larval mortality after 72 h. In standard laboratory conditions, the predation efficiency of golden wonder killifish, Aplocheilus lineatus, against A. stephensi IV instar larvae was 56.38 %, while in an aquatic environment treated with sub-lethal doses of the flower extract or AuNP, predation efficiency was boosted to 83.98 and 98.04 %, respectively. Lastly, the antiplasmodial activity of C. guianensis flower extract and AuNP was evaluated against CQ-resistant (CQ-r) and CQ-sensitive (CQ-s) strains of Plasmodium falciparum. IC50 of C. guianensis flower extract was 43.21 μg/ml (CQ-s) and 51.16 μg/ml (CQ-r). AuNP IC50 was 69.47 μg/ml (CQ-s) and 76.33 μg/ml (CQ-r). Overall, our results showed the multipurpose effectiveness of C. guianensis-synthesized AuNPs, since they may be proposed as newer and safer tools in the fight against CQ-r strains of P. falciparum and for field control of malaria vectors, in synergy with wonder killifish predators.

Eco-friendly control of malaria and arbovirus vectors using the mosquitofish Gambusia affinis and ultra-low dosages of Mimusops elengi-synthesized silver nanoparticles: towards an integrative approach?

Mosquito-borne diseases represent a deadly threat for millions of people worldwide. However, the use of synthetic insecticides to control Culicidae may lead to high operational costs and adverse non-target effects. Plant-borne compounds have been proposed for rapid extracellular synthesis of mosquitocidal nanoparticles. Their impact against biological control agents of mosquito larval populations has been poorly studied. We synthesized silver nanoparticles (AgNP) using the aqueous leaf extract of Mimusops elengi as a reducing and stabilizing agent. The formation of AgNP was studied using different biophysical methods, including UV-vis spectrophotometry, TEM, XRD, EDX and FTIR. Low doses of AgNP showed larvicidal and pupicidal toxicity against the malaria vector Anopheles stephensi and the arbovirus vector Aedes albopictus. AgNP LC50 against A. stephensi ranged from 12.53 (I instar larvae) to 23.55 ppm (pupae); LC50 against A. albopictus ranged from 11.72 ppm (I) to 21.46 ppm (pupae). In the field, the application of M. elengi extract and AgNP (10 × LC50) led to 100 % larval reduction after 72 h. In adulticidal experiments, AgNP showed LC50 of 13.7 ppm for A. stephensi and 14.7 ppm for A. albopictus. The predation efficiency of Gambusia affinis against A. stephensi and A. albopictus III instar larvae was 86.2 and 81.7 %, respectively. In AgNP-contaminated environments, predation was 93.7 and 88.6 %, respectively. This research demonstrates that M. elengi-synthesized AgNP may be employed at ultra-low doses to reduce larval populations of malaria and arbovirus vectors, without detrimental effects on predation rates of mosquito natural enemies, such as larvivorous fishes.

Direct and indirect effect of predators on Anopheles gambiae sensu stricto

The increased insecticides resistance by vectors and the ecological harm imposed by insecticides to beneficial organisms drawback mosquitoes chemical control efforts. Biological control would reduce insecticides tolerance and yet biodiversity friend. The predatory and non-predatory effects of Gambusia affinis and Carassius auratus on gravid Anopheles gambiae sensu strict and larvae survivorship were assessed. In determining predation rate, a single starved predator was exposed to third instar larvae of An. gambiae s.s. in different densities 20, 60 and 100. Six replicates in each of the densities for both predators, G. affinis and C. auratus, were set up. The larvae densities were monitored in every 12 and 24 h. In assessing indirect effects: An. gambiae s.s. first instar larvae of three densities 20, 60 and 100 were reared in water from a predator habitat and water from non-predator habitat. Larvae were monitored until they emerged to adults where larval survivorship and sex ratio (Female to total emerged mosquitoes) of the emerged adult from both water habitats were determined. Oviposition preference: twenty gravid females of An. gambiae s.s. were provided with three oviposition choices, one containing water from predator habitat without a predator, the second with water from a predator with a predator and the third with water from non-predatory habitat. The number of eggs laid on each container was counted daily. There were 20 replicates for each predator, G. affinis and C. auratus. Survivorship of An. gambiae s.s. larvae reared in water from non-predator habitat was higher than those reared in water from the predator habitats. Many males emerged in water from non-predatory water habitats while more females emerged from predator's habitats water. More eggs laid in tap water than in water from predator habitat and water from predator habitat with live predator. In 24 h, a starved C. auratus and G. affinis were able to consume 100% of the 3rd instar larvae. The findings from this study suggest that G. affinis and C. auratus may be useful in regulating mosquito populations in favour of beneficial insects. However, a small scale trial shall be needed in complex food chain system to ascertain the observed predation and kairomones effects.

Laboratory evaluation of predation on mosquito larvae by Australian mangrove fish

A series of laboratory experiments compared predation rates of three native eastern Australian mangrove fish species (Psuedomugil signifer, Hyseleotris galii, Pseudogobius sp.) and the exotic Gambusia holbrooki on 2nd and 4th instar Aedes vigilax larvae, in order to determine their potential as mosquito control agents in mangrove forests. All four species preyed on significant numbers of both 2nd and 4th instar larvae. All showed a similar pattern of larval consumption, gorging on larvae in the first hour of each experiment, before reducing to a relatively constant background feeding rate. Gambusia holbrooki showed the highest larval consumption rates, but is unsuitable as a mosquito control agent due to it being an exotic pest species in Australia. Of the three native species, P. signifer showed the greatest potential as a mosquito control agent, having consumption rates comparable to G. holbrooki, and was the only species that did not show a significant reduction in larval consumption in the night experiments.

ANOSPEX: a stochastic, spatially explicit model for studying Anopheles metapopulation dynamics

Anopheles mosquitoes transmit malaria, a major public health problem among many African countries. One of the most effective methods to control malaria is by controlling the Anopheles mosquito vectors that transmit the parasites. Mathematical models have both predictive and explorative utility to investigate the pros and cons of different malaria control strategies. We have developed a C++ based, stochastic spatially explicit model (ANOSPEX; Ano pheles Spatially-Explicit) to simulate Anopheles metapopulation dynamics. The model is biologically rich, parameterized by field data, and driven by field-collected weather data from Macha, Zambia. To preliminarily validate ANOSPEX, simulation results were compared to field mosquito collection data from Macha; simulated and observed dynamics were similar. The ANOSPEX model will be useful in a predictive and exploratory manner to develop, evaluate and implement traditional and novel strategies to control malaria, and for understanding the environmental forces driving Anopheles population dynamics.

Predation efficiency of Anopheles gambiae larvae by aquatic predators in western Kenya highlands

Background

The current status of insecticide resistance in mosquitoes and the effects of insecticides on non-target insect species have raised the need for alternative control methods for malaria vectors. Predation has been suggested as one of the important regulation mechanisms for malaria vectors in long-lasting aquatic habitats, but the predation efficiency of the potential predators is largely unknown in the highlands of western Kenya. In the current study, we examined the predation efficiency of five predators on Anopheles gambiae s.s larvae in 24 hour and semi- field evaluations.

Methods

Predators were collected from natural habitats and starved for 12 hours prior to starting experiments. Preliminary experiments were conducted to ascertain the larval stage most predated by each predator species. When each larval instar was subjected to predation, third instar larvae were predated at the highest rate. Third instar larvae of An. gambiae were introduced into artificial habitats with and without refugia at various larval densities. The numbers of surviving larvae were counted after 24 hours in 24. In semi-field experiments, the larvae were counted daily until they were all either consumed or had developed to the pupal stage. Polymerase chain reaction was used to confirm the presence of An. gambiae DNA in predator guts.

Results

Experiments found that habitat type (P < 0.0001) and predator species (P < 0.0001) had a significant impact on the predation rate in the 24 hour evaluations. In semi-field experiments, predator species (P < 0.0001) and habitat type (P < 0.0001) were significant factors in both the daily survival and the overall developmental time of larvae. Pupation rates took significantly longer in habitats with refugia. An. gambiae DNA was found in at least three out of ten midguts for all predator species. Gambusia affins was the most efficient, being three times more efficient than tadpoles.

Conclusion

These experiments provide insight into the efficiency of specific natural predators against mosquito larvae. These naturally occurring predators may be useful in biocontrol strategies for aquatic stage An. gambiae mosquitoes. Further investigations should be done in complex natural habitats for these predators.

Potential negative impacts and low effectiveness in the use of African annual killifish in the biocontrol of aquatic mosquito larvae in temporary water bodies

Commentary and discussion on a recent paper promoting the use of Nothobranchius guentheri, a small African annual fish from the Island of Zanzibar as a tool to control mosquito larvae in temporary bodies of freshwater throughout Africa is presented.

Arguments on major points; (1) expected low success of annual fish introductions, (2) low success of mosquito control in the field, (3) ecological threats, and (4) ethical issues are detailed.

Despite serious problems with mosquito-borne diseases in tropical Africa and elsewhere, we encourage responsible means of biological control of parasite vectors. We show that effectiveness of Nothobranchius translocations is low (the previous attempts failed), likelihood of effective mosquito larvae control under field condition is negligible and ecological threats from Nothobranchius translocations from within and outside the naturally occurring range are serious. We advocate against the proposed next step of the project, i.e. field trials in Tanzania.

The use of annual killifish in the biocontrol of the aquatic stages of mosquitoes in temporary bodies of fresh water; a potential new tool in vector control

BACKGROUND

Mosquitoes that breed in temporary pools in remote areas that dry up seasonally are especially difficult to control through chemical or biological means. The annual killifish has been suggested as a means of eradicating the aquatic stages of mosquitoes in transient pools because they can maintain permanent populations in such habitats by undergoing suspended animation or diapause during the embryonic stages to survive periodic drought. However, very little is known about the predatory activity of annual killifish and their usefulness in mosquito control.

RESULTS

The annual killifish, Nothobranchius guentheri, native to Tanzania, was used in this investigation. Food preference was tested under laboratory conditions by feeding juvenile killifish with 2nd instar mosquito larvae of Culex quinquefasciatus in the presence of alternative food sources, such as rotifers and chironomid larvae. Semi-field tests were conducted by introduction of hibernating killifish embryos and juvenile fish to artificial ponds in an outdoor open environment that allowed natural oviposition of Cx. quinquefasciatus. Food preference studies show that N. guentheri preferred to prey on mosquito larvae than either chironomid or rotifers. When hibernating killifish embryos were added to ponds simultaneously with the addition of freshwater, the embryos hatched and fed on mosquito larval population resulting in complete elimination of the immature stages. The introduction of juvenile fish to ponds with high density of mosquito larvae resulted in total eradication of the mosquito population due to predation by fish. Complete biocontrol of the mosquito larval population was achieved in the presence of 3 fish per m2 of pond surface area.

CONCLUSIONS

The annual killifish provides yet another tool that may be employed in the eradication diseases carried by mosquitoes through vector control, particularly in temporary bodies of freshwater. The fish can be conveniently transported in the absence of water in the form of hibernating embryos. Once introduced either as embryos or juveniles in ponds, the annual killifish can effectively reduce the larval population because of its aggressive predatory activity.

Identifying the most productive breeding sites for malaria mosquitoes in The Gambia

Background

Ideally larval control activities should be targeted at sites that generate the most adult vectors, thereby reducing operational costs. Despite the plethora of potential mosquito breeding sites found in the floodplains of the Gambia River, about 150 km from its mouth, during the rainy season, only a small proportion are colonized by anophelines on any day. This study aimed to determine the characteristics of larval habitats most frequently and most densely populated by anopheline larvae and to estimate the numbers of adults produced in different habitats.

Methods

A case-control design was used to identify characteristics of sites with or without mosquitoes. Sites were surveyed for their physical water properties and invertebrate fauna. The characteristics of 83 sites with anopheline larvae (cases) and 75 sites without (controls) were collected between June and November 2005. Weekly adult productivity was estimated with emergence traps in water-bodies commonly containing larvae.

Results

The presence of anopheline larvae was associated with high invertebrate diversity (Odds Ratio, OR 11.69, 95% CI 5.61–24.34, p < 0.001), the presence of emergent vegetation (OR 2.83, 95% CI 1.35–5.95, p = 0.006), and algae (at borderline significance; OR 1.87, 95% CI 0.96–3.618, p = 0.065). The density of larvae was reduced in sites that were larger than 100 m in perimeter (OR 0.151; 95% CI 0.060–0.381, p < 0.001), where water was tidal (OR 0.232; 95% CI 0.101–0.533, p = 0.001), vegetation shaded over 25% of the habitat (OR 0.352; 95% CI 0.136–0.911, p = 0.031) and water conductivity was above 2,000 μS/cm (OR 0.458; 95% CI 0.220–0.990, p = 0.048). Pools produced the highest numbers of Anopheles gambiae adults compared with rice fields, floodwater areas close to the edge of the floodplain or close to the river, and stream fringes. Pools were characterized by high water temperature and turbidity, low conductivity, increased presence of algae, and absence of tidal water.

Conclusion

There are few breeding sites that produce a high number of adult vectors in the middle reaches of the river in The Gambia, whereas those with low productivity are larger in area and can be found throughout the rainy season. Even though risk factors could be identified for the presence and density of larvae and productivity of habitats, the results indicate that anti-larval interventions in this area of The Gambia cannot be targeted in space or time during the rainy season.