Diving beetles (Dytiscidae) as predators of mosquito larvae (Culicidae) in field experiments and in laboratory tests of prey preference

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.

Predators as biocontrol agents of mosquito larvae in small and large habitats in Chiang Mai, Thailand

Controlling mosquito-borne disease is a major global challenge due to the rise of insecticide-resistant mosquitoes. In response, we conducted a study in Chiang Mai Province, Thailand, which is one of the largest and the most popular cities for tourists in Southeast Asia, to explore the potential of local species as biological control agents for mosquito larvae. Mosquito larvae and aquatic predators were sampled from large and small habitats, while relevant physico-chemical parameters were measured. The study identified 560 predators and 1,572 mosquitoes, with most mosquito species belonging to the genus Culex. Additionally, the study identified 16 predator taxa, including four fish taxa and 12 taxa of predatory aquatic insects belonging to four orders: Coleoptera, Hemiptera, Odonata, and Diptera. The study found that several locally occurring predator species, namely Poecillia, Laccophilus, Lutzia, Toxorhynchites splendens, Agrionoptera, and Pseudarion, shared habitats with mosquitoes, indicating their potential as effective biological control agents for mosquito control. Conductivity, dissolved oxygen, and pH were the important physico-chemical parameters that affect both predators and mosquito larvae. Consequently, promoting native predators and reducing mosquito larvae through habitat management would be a sustainable and ecologically friendly approach in large habitats where it is not possible to remove mosquito oviposition sites. In smaller habitats, releasing local aquatic predators and removing oviposition sites may be a suitable strategy.

Diversity oriented synthesis and SAR studies of new quinazolinones and related compounds as insecticidal agents against Culex pipiens L. Larvae and associated predator

The ongoing study reports the synthesis, spectroscopic analyses and larvicidal efficacy of novel series of quinazolinone derivatives and related compounds. The structures of the products were confirmed relied on their analytical and spectral data (IR, ¹H NMR, and ¹³C NMR). The spectral documentation promoted the successful isolation of the desirable compounds. The insecticidal activities of the synthesized compounds were assessed against laboratory and field strains of Culex pipiens larvae and a predator from the same ecological niche, Cybister tripunctatus. The results revealed that most of the tested compounds showed high potencies against lab strain of C. pipiens larvae with low resistance ratios in filed strain. In particular, compounds 15, 6 and 16 showed low LC₅₀ values, 0.094, 0.106, 0.129 (µg/mL), respectively against lab strain of C. pipiens larvae. The present study also explored the toxicity of tested compounds against field strain of non-target C. tripunctatus. Most of tested compounds were safer than temephos, especially 15 and 6 with SI/PSF values 96.746 and 83.167, respectively. Structure-activity relationship (SAR) was discussed the effect of substituents insertion on the derivatives activities. Quinazolinone derivatives and related compounds are promising compounds in the mosquito control programs and further studies are recommended to develop more effective derivatives and reveal their mode of action.

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.

Prey choice by a freshwater copepod on larval Aedes mosquitoes in the presence of alternative prey

Predator-prey interactions can have a significant impact on the abundance and distribution of species, but the outcome of these interactions is often context-dependent. In small freshwater habitats, predacious copepods are potential biological control agents for mosquito larvae. Through laboratory experiments, we tested if the presence of a non-mosquito prey (neonate Daphnia pulex) influenced prey selection of the predaceous copepod (Acanthocyclops vernalis) on 1^st instar Aedes mosquitoes (Aedes aegypti and Aedes albopictus). Copepods were starved for 12 h prior to being exposed to the two prey types (larval mosquitoes and Daphnia) at three densities: 25 mosquitoes:75 Daphnia, 50 mosquitoes:50 Daphnia, 75 mosquitoes:25 Daphnia. Single prey choice trials for each species as well as no-predator trials were also established for controls. Copepods were effective predators, with a single copepod consuming up to 37 1^st instar mosquito larvae during the 24-h trials. The number of mosquitoes consumed increased with their relative density, but the proportion of mosquitoes consumed was highest when Aedes made up only 25% of the population. Results from our study show that in a simple predator/two-prey system, two species of larval mosquitoes (Ae. aegypti and Ae. albopictus) are preferentially consumed over an alternative zooplankton by the copepod predator Acanthocyclops vernalis.

Mesocosm Experiments to Quantify Predation of Mosquito Larvae by Aquatic Predators to Determine Potential of Ecological Control of Malaria Vectors in Ethiopia

Malaria parasites are transmitted to humans by infectious female Anopheles mosquitoes. Chemical-insecticide-based mosquito control has been successful in reducing the burden of malaria. However, the emergence of insecticide resistance in malaria vectors and concerns about the effect of the chemicals on the environment, human health, and non-target organisms present a need for new or alternative vector control intervention tools. Biocontrol methods using aquatic invertebrate predators have emerged as a potential alternative and additional tool to control mosquito populations. Ecological control specifically makes use of species insights for improving the physical habitat conditions of competitors and predators of vectors. A first step towards this is to gain knowledge on the predation potential of several typically present macroinvertebrates. Hence, this study aimed at (1) examining the influence of the predation of hemipterans on the number of emerging adult mosquitoes and (2) detecting Anopheles mosquito DNA in the gut of those predators. The prey and predators were collected from a range of water bodies located in the Gilgel Gibe watershed, southwest Ethiopia. A semi-field study was carried out using mesocosms which were constructed using plastic containers mimicking the natural aquatic habitat of immature Anopheles mosquitoes. Adult mosquitoes that emerged from the mesocosms were collected using a mechanical aspirator. At the end of the experiment, predators were withdrawn from the mesocosms and identified to genus level. Polymerase Chain Reaction (PCR) was employed to identify sibling species of Anopheles gambiae s.l. and to detect Anopheles mosquito DNA in the gut of the predators. Data were analysed using R software. Giant water bugs (belostomatids) were the most aggressive predators of Anopheles larvae, followed by backswimmers (notonectids) and water boatmen (corixids). All female Anopheles gambiae s.l. emerged from the mesocosms were identified as Anopheles arabiensis. Anopheles arabiensis DNA was detected in the gut content of hemipteran specimens analysed from the three families. The number of the adult mosquitoes emerging from the mesocosms was affected by the presence of predators. The findings of this study provide evidence of the potential use of aquatic macroinvertebrate predators as biocontrol agents against immature Anopheles mosquitoes and their potential to be considered as a component of integrated vector management for insecticide resistance and the combined restoration of aquatic ecosystems via smart ecological engineering.

First record of the mosquito control potentiality of Stigmatogobius sadanundio (F. Hamilton, 1822) Gobiidae, Perciformes in laboratory condition

Background and Objectives:

In recent years, resurgence of mosquito-borne diseases has become a serious health problem in India. In the present study, Stigmatogobius sadanundio, a common indigenous fish, has been tested for its biocontrol potentiality for controlling Culex quinquefasciatus larvae. This small larvivorous fish can consume large number of Culex larvae even in the presence of alternate prey. This is the first report on the mosquito control ability of this fish.

Materials and Methods:

Experimental fishes were captured from tidal canals of Rupnarayan River in Purba Medinipur district, West Bengal. Mosquito larvae, pupae, and chironomid larvae were collected from Tamralipta municipality drainage system. Predation efficacy of the fish was evaluated on C. quinquefasciatus larvae and pupae as well as on Chironomus ramosus larvae which were collected from the drainage system of Tamralipta municipality and reared in the laboratory maintaining similar water parameters. Prey were offered to the fish separately and in paired combination to study its dietary preference.

Results:

S. sadanundio is a diurnal predator consuming significantly large number of prey during daytime. It prefers mosquito and chironomid larvae over mosquito pupae. The rate of predation was very high during 1^st h of predation. It consumed more chironomid larvae in the presence of mosquito larvae during daytime but consumed large number of mosquito larvae as compared to other larvivorous fish.

Conclusion:

S. sadanundio, an indigenous fish, is an effective biocontrol agent for the larvae of C. quinquefasciatus in laboratory condition. Even though the presence of alternate prey chironomid larvae influences the predation rate, it consumed large number of mosquito larvae. However, careful controlled field trials must be conducted before this fish is used as a biocontrol agent.

Bio-Control of Anopheles Mosquito Larvae Using Invertebrate Predators to Support Human Health Programs in Ethiopia

Mosquitoes have been a nuisance and health threat to humans for centuries due to their ability to transmit different infectious diseases. Biological control methods have emerged as an alternative or complementary approach to contain vector populations in light of the current spread of insecticide resistance in mosquitoes. Thus, this study aimed to evaluate the predation efficacy of selected potential predators against Anopheles mosquito larvae. Potential invertebrate predators and Anopheles larvae were collected from natural habitats, mainly (temporary) wetlands and ponds in southwest Ethiopia and experiments were conducted under laboratory conditions. Optimal predation conditions with respect to larval instar, water volume and number of predators were determined for each of the seven studied predators. Data analyses were carried out using the Poisson regression model using one way ANOVA at the 5% significant level. The backswimmer (Notonectidae) was the most aggressive predator on Anopheles mosquito larvae with a daily mean predation of 71.5 larvae (95% CI: [65.04;78.59]). Our study shows that larval instar, water volume and number of predators have a significant effect on each predator, except for dragonflies (Libellulidae), with regard to the preference of the larval instar. A selection of mosquito predators has the potential to control Anopheles mosquito larvae, suggesting that they can be used as complementary approach in an integrated malaria vector control strategy.

Match and mismatch: Integrating consumptive effects of predators, prey traits, and habitat selection in colonizing aquatic insects

Predators are a particularly critical component of habitat quality, as they affect survival, morphology, behavior, population size, and community structure through both consumptive and non-consumptive effects. Non-consumptive effects can often exceed consumptive effects, but their relative importance is undetermined in many systems. Our objective was to determine the consumptive and non-consumptive effects of a predaceous aquatic insect, Notonecta irrorata, on colonizing aquatic beetles. We tested how N. irrorata affected survival and habitat selection of colonizing aquatic beetles, how beetle traits contributed to their vulnerability to predation by N. irrorata, and how combined consumptive and non-consumptive effects affected populations and community structure. Predation vulnerabilities ranged from 0% to 95% mortality, with size, swimming, and exoskeleton traits generating species-specific vulnerabilities. Habitat selection ranged from predator avoidance to preferentially colonizing predator patches. Attraction of Dytiscidae to N. irrorata may be a natural ecological trap given similar cues produced by these taxa. Hence, species-specific habitat selection by prey can be either predator-avoidance responses that reduce consumptive effects, or responses that magnify predator effects. Notonecta irrorata had both strong consumptive and non-consumptive effects on populations and communities, while combined effects predicted even more distinct communities and populations across patches with or without predators. Our results illustrate that an aquatic invertebrate predator can have functionally unique consumptive effects on prey, attracting and repelling prey, while prey have functionally unique responses to predators. Determining species-specific consumptive and non-consumptive effects is important to understand patterns of species diversity across landscapes.

Relationships between predatory aquatic insects and mosquito larvae in residential areas in northern Thailand

In order to elucidate the poorly understood relationships between mosquito larvae and their predatory aquatic insects in urban and suburban areas of tropical Southeast Asia, where vector-borne diseases are prevalent, aquatic insects were sampled from 14 aquatic habitats in residential areas of Chiang Mai, northern Thailand, during the rainy season (July to November) in 2016. Correlations among biological variables, densities of major predatory aquatic insect groups (i.e., Odonata, Coleoptera, and Hemiptera: OCH group) in wetlands and artificial lentic habitats, and the density of mosquito larvae were analyzed. Among the sampled mosquito larvae, Culex spp. were the most abundant, and both OCH density and water quality were major determinants of Culex spp. density (r_s = -0.302 and -0.396, respectively). Logistic regression analyses indicated that the probability of Culex spp. occurrence was significantly and negatively correlated with OCH density. Furthermore, high macrophyte abundance was associated with higher predator density, potentially reducing mosquito density. Hemipteran predators were most negatively correlated with Culex spp. density, regardless of whether macrophyte abundance was high or low (r_s = -0.547 and -0.533, respectively). Therefore, hemipteran predators were the most important aquatic insect predators in the urban and suburban residential areas of Chiang Mai, Thailand, and OCH species, such as the hemipteran Micronecta scutellaris, could be used as biological control agents against mosquitoes in the region.

Elucidating stygofaunal trophic web interactions via isotopic ecology

Subterranean ecosystems host highly adapted aquatic invertebrate biota which play a key role in sustaining groundwater ecological functioning and hydrological dynamics. However, functional biodiversity studies in groundwater environments, the main source of unfrozen freshwater on Earth, are scarce, probably due to the cryptic nature of the systems. To address this, we investigate groundwater trophic ecology via stable isotope analysis, employing δ¹³C and δ¹⁵N in bulk tissues, and amino acids. Specimens were collected from a shallow calcrete aquifer in the arid Yilgarn region of Western Australia: a well-known hot-spot for stygofaunal biodiversity. Sampling campaigns were carried out during dry (low rainfall: LR) and the wet (high rainfall: HR) periods. δ¹³C values indicate that most of the stygofauna shifted towards more ¹³C-depleted carbon sources under HR, suggesting a preference for fresher organic matter. Conversion of δ¹⁵N values in glutamic acid and phenylalanine to a trophic index showed broadly stable trophic levels with organisms clustering as low-level secondary consumers. However, mixing models indicate that HR conditions trigger changes in dietary preferences, with increasing predation of amphipods by beetle larvae. Overall, stygofauna showed a tendency towards opportunistic and omnivorous habits—typical of an ecologically tolerant community—shaped by bottom-up controls linked with changes in carbon flows. This study provides baseline biochemical and ecological data for stygofaunal trophic interactions in calcretes. Further studies on the carbon inputs and taxa-specific physiology will help refine the interpretation of the energy flows shaping biodiversity in groundwaters. This will aid understanding of groundwater ecosystem functioning and allow modelling of the impact of future climate change factors such as aridification.

Ultrastructure and morphology of antennal sensilla of the adult diving beetle Cybister japonicus Sharp

The morphology and distribution of the antennal sensilla of adult diving beetle Cybister japonicus Sharp (Dytiscidae, Coleoptera), have been examined. Five types of sensilla on the antennae were identified by scanning electron microscope (SEM) and transmission electron microscope (TEM). Sensilla placodea and elongated s. placodea are the most abundant types of sensilla, distributing only on the flagellum. Both these types of sensilla carry multiple pore systems with a typical function as chemoreceptors. Three types of s. coeloconica (Type I–III) were also identified, with the characterization of the pit-in-pit style, and carrying pegs externally different from each other. Our data indicated that both type I and type II of s. coleconica contain two bipolar neurons, while the type III of s. coleconica contains three dendrites in the peg. Two sensory dendrites in the former two sensilla are tightly embedded inside the dendrite sheath, with no space left for sensilla lymph. There are no specific morphological differences in the antennal sensilla observed between males and females, except that the males have longer antennae and more sensilla than the females.

Oviposition of Culex tarsalis (Diptera: Culicidae) Differs on Water Conditioned by Potential Fish and Insect Predators

The response of egg-laying Culex tarsalis Coquillett (Diptera: Culicidae) to water conditioned by three fish species used for mosquito control and three predatory aquatic insect species was examined in laboratory binary choice experiments. Oviposition by Cx. tarsalis was 72% less on water conditioned with the arroyo chub, Gila orcutti (Eigenmann & Eigenmann) (Cypriniformes: Cyprinidae) relative to control cups containing aged tap water, but no significant difference was found in the numbers of egg rafts laid on water conditioned with the fathead minnow (Pimephales promelas (Rafinesque), Cypriniformes: Cyprinidae) and the control treatment (water aged 24 h). Mosquito oviposition on water conditioned with the predominantly herbivorous/algivorous California Mozambique tilapia hybrid (Oreochromis mossambicus (Peters) × Oreochromis urolepis hornorum L. (Perciformes: Cichlidae)) or predatory insects (nymphs: Sympetrum corruptum (Hagen) (Odonata: Libellulidae); adults: Thermonectus basillaris (Harris) or Cybister fimbriolatus (Say) (Coleoptera: Dytiscidae)) did not differ significantly relative to that onto water aged for 24 h. As compared with water aged 24 h and water conditioned with diving beetles, oviposition by Cx. tarsalis was significantly lower (≥53%) when live predatory diving beetles were present in oviposition cups. Gravid Cx. tarsalis females do not respond equally to putative semiochemicals in water conditioned with the piscine or aquatic insect predators of immature mosquitoes tested here.

Male tarsi specific odorant-binding proteins in the diving beetle Cybister japonicus sharp

Odorant binding proteins (OBPs) play critical roles in chemical communication of insects, as they recognize and transport environmental chemical signals to receptors. The diving beetle Cybister japonicus Sharp shows a remarkable sexual dimorphism. The foreleg tarsi of males are equipped with large suction cups, believed to help holding the female during underwater courtship and mating. Here, we identified two OBPs highly and specifically expressed in male tarsi, suggesting important functions of these structures in chemical communication. The first protein, CjapOBP1, exhibits the 6 conserved cysteines motif of classic OBPs, while the second, CjapOBP2, contains only four cysteines and can be assigned to the sub-class of C-minus OBPs. Both proteins were expressed in a bacterial system and the purified recombinant proteins were used to for antibodies preparation. Western Blot analysis showed that CjapOBP1 is predominantly expressed in male tarsi and could be also detected in antennae and palpi of both sexes, while CjapOBP2, besides male tarsi, is also present in testis. Ligand-binding experiments showed a good binding affinity between CjapOBP1, CjapOBP2 and citral and coniferyl aldehyde, respectively. These results support a possible function of these two OBPs in the male foreleg tarsi of diving beetles in chemical communication.

Making green infrastructure healthier infrastructure

Increasing urban green and blue structure is often pointed out to be critical for sustainable development and climate change adaptation, which has led to the rapid expansion of greening activities in cities throughout the world. This process is likely to have a direct impact on the citizens' quality of life and public health. However, alongside numerous benefits, green and blue infrastructure also has the potential to create unexpected, undesirable, side-effects for health. This paper considers several potential harmful public health effects that might result from increased urban biodiversity, urban bodies of water, and urban tree cover projects. It does so with the intent of improving awareness and motivating preventive measures when designing and initiating such projects. Although biodiversity has been found to be associated with physiological benefits for humans in several studies, efforts to increase the biodiversity of urban environments may also promote the introduction and survival of vector or host organisms for infectious pathogens with resulting spread of a variety of diseases. In addition, more green connectivity in urban areas may potentiate the role of rats and ticks in the spread of infectious diseases. Bodies of water and wetlands play a crucial role in the urban climate adaptation and mitigation process. However, they also provide habitats for mosquitoes and toxic algal blooms. Finally, increasing urban green space may also adversely affect citizens allergic to pollen. Increased awareness of the potential hazards of urban green and blue infrastructure should not be a reason to stop or scale back projects. Instead, incorporating public health awareness and interventions into urban planning at the earliest stages can help insure that green and blue infrastructure achieves full potential for health promotion.

Relations Between the Structure of Benthic Macro-Invertebrates and the Composition of Adult Water Beetle Diets from the Dytiscidae Family

This paper investigates the relations between the diet structure of predaceous adult water beetles from the Dytiscidae family and the structure of macrofauna inhabiting the same environments. The field studies were carried out from April until September in 2012 and 2013 in 1-mo intervals. In total, >1,000 water beetles and 5,115 benthic macro-invertebrates were collected during the whole period of the study. Subsequently, 784 specimens of adult water beetles (70.6% out of the total sampled) with benthic macro-invertebrates found in their proventriculi, were subject to analysis. The predators were divided into three categories depending on their body size: small beetles (2.3-5.0 mm), medium-sized beetles (13-15 mm), and large beetles (27-37 mm). All adult Dytiscidae consumed primarily Ephemeroptera and Chironomidae larvae. Although Asellidae were numerically dominant inhabitants of the sites, the adult water beetles did not feed on them. The analysis of feeding relations between predators and their prey revealed that abundance of Ephemeroptera, Chironomidae, and larval Dytiscidae between the environment and the diet of adult Dytiscidae were strongly correlated.

Specific detection of the floodwater mosquitoes Aedes sticticus and Aedes vexans DNA in predatory diving beetles

Floodwater mosquitoes (Diptera: Culicidae) are associated with periodically flooded wet meadows, marshes, and swamps in floodplains of major rivers worldwide, and their larvae are abundant in the shallow parts of flooded areas. The nuisance caused by the blood-seeking adult female mosquitoes motivates mosquito control. Larviciding with Bacillus thuringiensis israelensis is considered the most environmentally safe method. However, some concern has been raised whether aquatic predatory insects could be indirectly affected by this reduction in a potential vital prey. Top predators in the temporary wetlands in the River Dalälven floodplains are diving beetles (Coleoptera: Dytiscidae), and Aedes sticticus and Ae. vexans are the target species for mosquito control. For detailed studies on this aquatic predator-prey system, we developed a polymerase chain reaction (PCR) assay for detection of mosquito DNA in the guts of medium-sized diving beetles. Primers were designed for amplifying short mitochondrial DNA fragments of the cytochrome C oxidase subunit I (COI) gene in Ae. sticticus and Ae. vexans, respectively. Primer specificity was confirmed and half-life detectability of Ae. sticticus DNA in diving beetle guts was derived from a feeding and digestion experiment. The Ae. sticticus DNA within diving beetle guts was detected up to 12 h postfeeding, and half-life detectability was estimated to 5.6 h. In addition, field caught diving beetles were screened for Ae. sticticus and Ae. vexans DNA and in 14% of the diving beetles one or both mosquito species were detected, showing that these mosquito species are utilized as food by the diving beetles.

Prey preferences of aquatic insects: potential implications for the regulation of wetland mosquitoes

Wetlands are potential sites for mosquito breeding and are thus important in the context of public health. The use of chemical and microbial controls is constrained in wetlands in view of their potential impact on the diverse biota. Biological control using generalist aquatic insects can be effective, provided a preference for mosquito larvae is exhibited. The mosquito prey preferences of water bugs and larvae of odonate species were evaluated using chironomid larvae, fish fingerlings and tadpoles as alternative prey. Manly's selectivity (αi ) values with 95% confidence intervals (CIs) were estimated to judge prey preference patterns. Multivariate analysis of variance (manova) and standardized canonical coefficients were used to test the effects of density on prey selectivity. The αi values indicated a significant preference (P < 0.05) in all of the insect predators tested for mosquito larvae over the alternative prey as a density-dependent function. On a comparative scale, chironomid larvae had the highest impact as alternative prey. In a multiple-prey experiment, predators showed a similar pattern of preference for mosquito larvae over alternative prey, reflecting a significant (P < 0.05) niche overlap. The results suggest that, in a laboratory setting, these insect predators can effectively reduce mosquito density in the presence of multiple alternative prey.

Who eats whom in a pool? A comparative study of prey selectivity by predatory aquatic insects

Predatory aquatic insects are a diverse group comprising top predators in small fishless water bodies. Knowledge of their diet composition is fragmentary, which hinders the understanding of mechanisms maintaining their high local diversity and of their impacts on local food web structure and dynamics. We conducted multiple-choice predation experiments using nine common species of predatory aquatic insects, including adult and larval Coleoptera, adult Heteroptera and larval Odonata, and complemented them with literature survey of similar experiments. All predators in our experiments fed selectively on the seven prey species offered, and vulnerability to predation varied strongly between the prey. The predators most often preferred dipteran larvae; previous studies further reported preferences for cladocerans. Diet overlaps between all predator pairs and predator overlaps between all prey pairs were non-zero. Modularity analysis separated all primarily nectonic predator and prey species from two groups of large and small benthic predators and their prey. These results, together with limited evidence from the literature, suggest a highly interconnected food web with several modules, in which similarly sized predators from the same microhabitat are likely to compete strongly for resources in the field (observed Pianka’s diet overlap indices >0.85). Our experiments further imply that ontogenetic diet shifts are common in predatory aquatic insects, although we observed higher diet overlaps than previously reported. Hence, individuals may or may not shift between food web modules during ontogeny.

Malaria vector control: from past to future

Malaria is one of the most common vector-borne diseases widespread in the tropical and subtropical regions. Despite considerable success of malaria control programs in the past, malaria still continues as a major public health problem in several countries. Vector control is an essential part for reducing malaria transmission and became less effective in recent years, due to many technical and administrative reasons, including poor or no adoption of alternative tools. Of the different strategies available for vector control, the most successful are indoor residual spraying and insecticide-treated nets (ITNs), including long-lasting ITNs and materials. Earlier DDT spray has shown spectacular success in decimating disease vectors but resulted in development of insecticide resistance, and to control the resistant mosquitoes, organophosphates, carbamates, and synthetic pyrethroids were introduced in indoor residual spraying with needed success but subsequently resulted in the development of widespread multiple insecticide resistance in vectors. Vector control in many countries still use insecticides in the absence of viable alternatives. Few developments for vector control, using ovitraps, space spray, biological control agents, etc., were encouraging when used in limited scale. Likewise, recent introduction of safer vector control agents, such as insect growth regulators, biocontrol agents, and natural plant products have yet to gain the needed scale of utility for vector control. Bacterial pesticides are promising and are effective in many countries. Environmental management has shown sufficient promise for vector control and disease management but still needs advocacy for inter-sectoral coordination and sometimes are very work-intensive. The more recent genetic manipulation and sterile insect techniques are under development and consideration for use in routine vector control and for these, standardized procedures and methods are available but need thorough understanding of biology, ethical considerations, and sufficiently trained manpower for implementation being technically intensive methods. All the methods mentioned in the review that are being implemented or proposed for implementation needs effective inter-sectoral coordination and community participation. The latest strategy is evolution-proof insecticides that include fungal biopesticides, Wolbachia, and Denso virus that essentially manipulate the life cycle of the mosquitoes were found effective but needs more research. However, for effective vector control, integrated vector management methods, involving use of combination of effective tools, is needed and is also suggested by Global Malaria Control Strategy. This review article raises issues associated with the present-day vector control strategies and state opportunities with a focus on ongoing research and recent advances to enable to sustain the gains achieved so far.

The influence of aquatic predators on mosquito abundance in animal drinking troughs in New Zealand

The occurrence and abundance of mosquito populations may be associated with the abundance of predators. We examined the relationship between aquatic predators and populations of mosquitoes in animal water troughs in Waikanae, New Zealand. We also investigated the effects of water volume and environmental factors (temperature, rainfall, wind speed, humidity, and pressure) in order to further understand factors influencing mosquito and predator populations. Logistic regression indicated that the presence or absence of mosquitoes was primarily affected by three factors: predator abundance, week of observation, and water volume. Pearson's correlation indicated that the presence of predators had a positive correlation with water volume (r² = 0.176, p< 0.05). Otherwise, the presence of mosquito larvae in water troughs was negatively correlated with water volume (r² =-0.159, p=0.022) and wind speed (r² =0.142, p=0.041). We established a translocation experiment in which predators or mosquitoes were moved between troughs in order to examine the prey survival rate after exposure to Anisops wakefieldi predators. The survival rate of mosquitoes was not significantly different, between 0-0.1%, irrespective of the number of predators translocated (1-9) or the initial mosquito density (20-70 larvae). Our results suggested that A. wakefieldi predators may have the potential to be a promising biological control tool for the control of mosquito populations by altering mosquito population dynamics.

The roles of predators, competitors, and secondary salinization in structuring mosquito (Diptera: Culicidae) assemblages in ephemeral water bodies of the Wheatbelt of Western Australia

Studies that consider both biotic and abiotic determinants of organisms are rare, but critical to delineate underlying determinants of community richness (number of taxa) and abundance (number of larvae per water body). In this study, we consider the importance of disturbance (salinity) and predator and competitor variables on mosquitoes (Diptera: Culicidae) in small ephemeral water bodies across the Wheatbelt of Western Australia. Similar to mosquitoes, and contrary to general perceptions, nonculicid aquatic fauna (aquatic fauna) had a common occurrence (number or percentage of water bodies occupied) and were abundant (average density) in ephemeral water bodies, albeit with a simplified trophic structure. The occurrence and density (number per unit area) of aquatic fauna between water bodies were highly variable, but general relationships of aquatic fauna with rainfall, water body surface area, salinity, and mosquitoes were apparent. In contrast to mosquitoes, the density of aquatic fauna declined with recent rainfall, implying mosquitoes may colonize newly created water bodies more quickly than aquatic fauna. Assemblages (richness and density of taxa) of aquatic fauna changed along a salinity gradient, as did mosquitoes, and this was pronounced for predator groups. Densities of mosquitoes were not limited by any single taxonomic group, by a negative relationship. However, the density and richness of mosquitoes generally declined in association with increased richness of predators and density of all other taxa (taxa not specifically classified as predators or competitors of mosquitoes). These relationships may account for higher densities of mosquitoes in smaller water bodies, where richness of predators is reduced and the density of other taxa does not differ from larger water bodies. Our results also suggest salinity in the Western Australia Wheatbelt may facilitate greater abundance of halotolerant mosquitoes, Aedes alboannulatus Macquart and Aedes camptorhynchus Thomson (a vector of Ross River virus [Togoviridae: Alphavirus]), by releasing them from biotic regulation.

Predatory ability of adult diving beetles on the Japanese encephalitis vector Culex tritaeniorhynchus

The predatory ability of adult Japanese diving beetles on 4th instars of the Japanese encephalitis vector mosquito, Culex tritaeniorhynchus, was assessed under laboratory conditions. To determine the differences in the predatory ability among 14 beetle species inhabiting rice fields, the following species were introduced to 10 Cx. tritaeniorhynchus 4th instars in a plastic cup: 5 small-bodied species (< 9 mm in body length) comprising Hydroglyphus japonicus, Noterus japonicus, Laccophilus difficilis, Hyphydrus japonicus, and Agabusjaponicus; 7 medium-bodied species (9-20 mm in body length) comprising Hydaticus rhantoides, Hydaticus grammicus, Rhantus suturalis, Eretes griseus, Hydaticus bowringii, Agabus conspicuous, and Graphoderus adamsii; and 2 large-bodied species (> 20 mm) comprising Cybister brevis and C. japonicus. The average 24-h predation rate was highest in medium-bodied species (> 90%), followed by small-bodied species (31%) and large-bodied species (19%). The functional responses to Cx. tritaeniorhynchus larvae of 3 medium-bodied species (H. grammicus, R. suturalis, and E. griseus) were estimated. Eretes griseus exhibited the highest attach rate and shortest prey-handling time, suggesting that medium-bodied diving beetles, especially E. griseus, may be efficient predators of mosquito larvae in rice fields.

Explaining abundance-occupancy relationships in specialists and generalists: a case study on aquatic macroinvertebrates in standing waters

1. A positive interspecific abundance-occupancy relationship is one of the most robust patterns in macroecology. Yet, the mechanisms driving this pattern are poorly understood. Here, we use biological traits of freshwater macroinvertebrates to gain a mechanistic understanding and disentangle the various explanations. We ask whether mechanisms underlying the abundance-occupancy relationship differ between species, and whether information on individual species can be used to explain their contribution to the interspecific relationship. 2. We test the hypothesis that the importance of metapopulation dynamics or niche differences in explaining the relationship differs between species, varying in relation to their habitat breadth. In addition, we analyse how a species' biological traits shape its habitat breadth and its abundance and occupancy. 3. The abundance and occupancy of the 234 different aquatic macroinvertebrate species were strongly and positively related. Marked differences were found between habitat specialists and habitat generalists in the goodness-of-fit of abundance-occupancy relationships. The occupancy-frequency distribution was bimodal for habitat generalists, allowing 'satellite species' to be distinguished from 'core species'. 4. Habitat generalists appeared to be more widespread but less abundant than habitat specialists, suggesting that the jack-of-all-trades may be master-of-none. Species traits (trophic position and other life-history traits) explained a significant part of the variation around the general relationship. Among habitat specialists, more species showed synchronized life cycles, a low dispersal capacity or clustered oviposition, being better adapted to predictable habitats. Among habitat generalists, more species had long-lived adults, spreading reproductive effort in time and space, and were strong dispersers, being better adapted to unpredictable habitats. 5. Interspecific abundance-occupancy relationships can be best understood by examining the contribution of individual species. For habitat specialists, the interplay between niche differences (diet and habitat use) and the underlying spatial distribution of environmental conditions result in competitive displacement and differences in species' success. For habitat generalists, differences in colonization and extinction rates between species are more important. Therefore, both metapopulation dynamics and niche differences can operate simultaneously but apply to different species, thus constituting different endpoints of the same continuum.

Ontogenetic dietary shift in the larvae of Cybister japonicus (Coleoptera: Dytiscidae) in Japanese rice fields

A number of fragmentary reports suggest that the endangered diving beetle Cybister japonicus larvae feed on tadpoles, fish, and aquatic insects. However, no quantitative study on the feeding habits of C. japonicus larvae has been reported. In this study, field observations and rearing experiments were carried out to show the feeding ecology of C. japonicus larvae. Unlike previous commentaries, the first- and second-instar larvae of C. japonicus preyed on insects, mainly Odonata nymphs and Notonecta triguttata, irrespective of prey availability, but did not eat vertebrates such as tadpoles and fish in the field. On the contrary, the third-instar larvae fed on both insects and vertebrates. Rearing experiments showed that the number of Odonata nymphs consumed was significantly more than the number of tadpoles consumed by the first and second instars but third-instar larvae ate both the Odonata nymphs and tadpoles in the tadpole-Odonata nymph mixture experiment. The total body lengths of C. japonicus new adults in the Odonata nymph and tadpole-Odonata nymph mixture treatments were statistically equal. These results suggested that the first- and second-instar larvae of C. japonicus prey mainly on insects and do not eat vertebrate animals (insectivore), whereas the third-instar larvae fed on both insects and vertebrates (generalist).

Biocontrol of larval mosquitoes by Acilius sulcatus (Coleoptera: Dytiscidae)

Background

Problems associated with resistant mosquitoes and the effects on non-target species by chemicals, evoke a reason to find alternative methods to control mosquitoes, like the use of natural predators. In this regard, aquatic coleopterans have been explored less compared to other insect predators. In the present study, an evaluation of the role of the larvae of Acilius sulcatus Linnaeus 1758 (Coleoptera: Dytiscidae) as predator of mosquito immatures was made in the laboratory. Its efficacy under field condition was also determined to emphasize its potential as bio-control agent of mosquitoes.

Methods

In the laboratory, the predation potential of the larvae of A. sulcatus was assessed using the larvae of Culex quinquefasciatus Say 1823 (Diptera: Culicidae) as prey at varying predator and prey densities and available space. Under field conditions, the effectiveness of the larvae of A. sulcatus was evaluated through augmentative release in ten cemented tanks hosting immatures of different mosquito species at varying density. The dip density changes in the mosquito immatures were used as indicator for the effectiveness of A. sulcatus larvae.

Results

A single larva of A. sulcatus consumed on an average 34 IV instar larvae of Cx. quinquefasciatus in a 24 h period. It was observed that feeding rate of A. sulcatus did not differ between the light-on (6 a.m. – 6 p.m.), and dark (6 p.m. – 6 a.m.) phases, but decreased with the volume of water i.e., space availability. The prey consumption of the larvae of A. sulcatus differed significantly (P < 0.05) with different prey, predator and volume combinations, revealed through univariate ANOVA. The field study revealed a significant decrease (p < 0.05) in larval density of different species of mosquitoes after 30 days from the introduction of A. sulcatus larvae, while with the withdrawal, a significant increase (p < 0.05) in larval density was noted indicating the efficacy of A. sulcatus in regulating mosquito immatures. In the control tanks, mean larval density did not differ (p > 0.05) throughout the study period.

Conclusion

the larvae of the dytiscid beetle A. sulcatus proved to be an efficient predator of mosquito immatures and may be useful in biocontrol of medically important mosquitoes.

Biocontrol efficiency of odonate nymphs against larvae of the mosquito, Culex quinquefasciatus Say, 1823

An estimation of the predatory efficiency of the nymphs of five coexisting odonate species Aeshna flavifrons, Coenagrion kashmirum, Ischnura forcipata, Rhinocypha ignipennis and Sympetrum durum using the fourth-instar larvae of Culex quinquefasciatus as prey, was made under laboratory and semi-field conditions. The daily feeding rate varied among the odonate species, at laboratory conditions. The mean number of IV instars Cx. quinquefasciatus larvae killed per day, ranged between 14 and 64 (64 mosquito larvae for I. forcipata, 57 for A. flavifrons, 45 for R. ignipennis, 25 for S. durum and 14 for C. kashmirum). The prey consumption was linearly related to the number of predators and prey available but inversely related with space. It was also noted that the feeding rates varied significantly between dark and light conditions, in all the odonate species. The presence of nymphs in semi-field conditions significantly lowered the mosquito larval density in dipper samples after 15 days from the introduction, followed by a significant increase of larval mosquito density after 15 days from the withdrawal of the nymphs. The results of the present observations are suggestive of the use of odonate nymphs in temporary pools or larger habitats where they can be a potential biological resource in regulating the larval population of the vector and pest mosquitoes.

Interactions between mosquito larvae and species that share the same trophic level

Ecological theory predicts, and empirical research shows, that species sharing the same trophic level as a target species (hereafter controphic species) can have large direct and indirect effects on the target species by sharing resources and/or by serving as alternative prey to predators. Yet, the roles of controphic species of mosquito larvae in affecting mosquito populations have received little attention. Published empirical evidence, although scarce, suggests that controphic species such as zooplankton and anuran larvae compete with mosquito larvae, can positively affect mosquito larvae by consuming bacteria that are pathogenic to mosquito larvae, reduce predation on mosquito larvae by serving as alternative prey, and ultimately cause increased predation on mosquito larvae by causing a numerical response in the predator. We conclude that more extensive theoretical and empirical studies in elucidating the roles of controphic species will better allow us to predict mosquito population dynamics and allow for better management of mosquitoes.