Biological Control Of Mosquito Larvae Research Articles

Toxicity Evaluation and Genetic Improvement of Bacillus thuringiensis Isolated from Different Regions in Assiut, Egypt against Mosquito Larvae

This study aims to evaluate the toxicity and genetic improvement of Bacillus thuringiensis isolates. Isolates were obtained from soil, insect and water samples from different regions of Assiut, Egypt for biological control of mosquito larvae. B. thuringiensis colonies were identified based on morphological and then by PCR which detect the Cry toxic genes in the isolates. Bioassays were performed to evaluate the toxicity of different strains of B. thuringiensis against mosquito larvae such as (Culex spp). In general, 36 B. thuringiensis isolates were obtained (31 from soil, 4 from insects, and 1 from water). And they were all toxic to mosquito larvae with different mortality percentages from 7 to 97% after 48 hours. Isolate Am2 recorded the highest mortality percentage 97% and Mn3 lowest mortality percentage 7%. PCR revealed that Am2 isolate which caused the highest mortality encodes three different types of Cry toxins, Cyt1AA, Cry1Ac and Cry2Aa. This isolate Am2 was examined by scanning electron microscopy to observe the shape of the Cry proteins. The results showed that the Am2 isolate contained of spherical and cuboidal toxic proteins. Then UV-mutagenesis was performed on the Am2 isolate to improve its toxicity. Out of 30 obtained UV-mutants, only one mutant showed improvement in the mortality of mosquito larvae since it caused a mortality rate of 100%. The results of the present study revealed the larvicidal efficacy of B. thuringiensis (Am2) isolate found in the soil of Assiut, could be used in biological control program of mosquito larvae.

Comparative efficacy of natural aquatic predators for biological control of mosquito larvae: A neglected tool for vector control.

Mosquitoes are a dominant fraction of dipteran fauna, occupying a variety of niches. The most common method deployed for their control is the use of insecticides. Throughout their life cycle they are exposed to a wide range of predators in different habitats, thus biological control of mosquitoes by using aquatic predators has been suggested. Therefore, the present study was carried out to explore the type of natural predators coexisting with the mosquito larvae in still water bodies and to determine their efficacy as predators for mosquito larvae. A coexistence of different predators with mosquito larvae was observed in 27 standing water bodies of Chandigarh, India. The predation efficiency of tadpoles of frog was comparable to Gambusia fish, as 97% of the mosquito larvae of all instars of the medically important mosquito genera Anopheles, Aedes, Culex and Armigeres were preyed. The toad tadpoles were found to be least effective and their predation rate was found to be negligible. Further studies on larval source management by frog tadpoles in combination with insecticides or stand-alone would be worthwhile.

The freshwater copepod genus <i>Mesocyclops </i> (Copepoda, Cyclopoida, Cyclopidae) in Vietnam

The freshwater copepod Mesocyclops Sar, 1914, a species-rich genus within the family Cyclopoidae Rafinesque, 1815, is common in tropical areas. In addition, the genus members are used for the biological control of mosquito larvae (Anopheles, Aedes) which are vectors for transmitting dengue fever. In Vietnam, a total of 11 Mesocyclops species have been recorded in inland freshwater bodies. Of which, one endemic species (M. sondoongensis Tran & Hołyńska, 2015) and two species were described from Vietnam, namely M. yenae Hołyńska, 1998; M. ferjemurami Hołyńska & Vu, 2000. Diagnostic characteristics, habitat, and distribution of all 11 species are provided. Additionally, a pictorial key to all Vietnamese Mesocyclops is presented.

Survival of the copepod Mesocyclops longisetus during simulations of transport from hatchery to target areas for biological control of mosquito larvae

Copepods have been successfully used in many countries for the biological control of larvae of mosquitoes that vector diseases. In Brazil, this line of research has been focused on the use of the copepod Mesocyclops longisetus (Thiébaud, 1914) for the biological control of the mosquito Aedes aegypti (Linnaeus, 1792). The transportation of the copepods from the place where they are reared to where they will be used often involves long distances for extended periods of time. This study assesses the survivorship of M. longisetus during simulation of transport under different conditions. Different loading densities (20, 30, 40, 80, and 120 ind.L) and stirring times (30 minutes, one hour, two hours, and four hours) were tested. Survivorship was high, with 75% of the results equal or higher than 90% survival. Reduced mortality was observed when transportation time was up to 120 minutes and densities were up to 40 ind.L. In higher densities or longer transportation times, the mortality rate was significantly affected.

Complementary impacts of heterospecific predators facilitate improved biological control of mosquito larvae

Natural enemies can play a critical role in regulating pests, with simplified ecosystems often favoring pest proliferation via reduced predation pressure. As predator-predator interactions and size refuge effects directly influence prey risk, an understanding of multiple predator effects across prey ontogeny could be useful for quantifying natural enemy impacts on target populations. In the present study, we used functional responses (FRs) to quantify the combined predatory impacts of a copepod, Lovenula falcifera (Copepoda: Diaptomidae), and a notonectid, Anisops sardea (Hemiptera: Notonectidae), on Culex pipiens larvae over the course of their development. The impacts of copepods and notonectids differed across larval mosquito ontogeny. Copepods were most efficient consumers of early instar mosquitoes, but were unable to handle larger late instars, whereas notonectids were most effective against later instars. Both predators exhibited Type II FRs and typically contributed additively to prey risk, with synergistic impacts evident on prey of intermediate sizes. Thus, community diversity can potentially facilitate improved predatory impacts on larval mosquitoes across their ontogeny. The additive feeding rates of this copepod-notonectid combination suggests a lack of interference among these predators. Therefore, the promotion and conservation of such complementary predator assemblages in temporary wetlands can be recommended to suppress populations of mosquitoes which vector pathogens and parasites.

Native larvivorous fish diversity as a biological control agent against mosquito larvae in an endemic malarious region of Ranchi district in Jharkhand, India

Mosquitoes are responsible for transmitting several diseases, including malaria, dengue, chikungunya, filariasis, and yellow fever, etc. Release of larvivorous fishes is one of the cheapest method of vector management approach, with long suppression of mosquito population. The present study identifies the native larvivorous fishes and evaluates their potential larvivoracity for biological control of mosquito larvae in an endemic malarious region. During the year 2012-13, an ecological descriptive study was carried out in diverse aquatic habitats of fish species found in different areas of Ranchi district, in Jharkhand state of India. Fishes were captured using fishing nets, and identified and classified according to the available keys. Their larvivorous potential was graded according to their feeding potential. Data on current conservation status as well as their abundance were also recorded and analysed. In total, 30 larvivorous fish species belonging to seven orders, 10 families and 21 genera were identified. Order Cypriniformes and the family Cyprinidae were the most ascendant group constituting 66.7 and 60%, respectively. The grading assessment of larvivorous potential for different fish species revealed that, Colisa fasciatus possess maximum larvivoracity (+ + + + +). According to the conservation, assessment and management plan (CAMP, 1998), 60% species were at lower risk near threat (LRnt), while 86.7% species were at least concerned (LC) as per the IUCN, 2017 categorisation. All fish species preferred to inhabit in freshwater. Maximum species occurrence was found in the river (63.3%). Only 30% species were bottom feeders (BF). The larvivoracity and habitat distribution analysis indicated that C. fasciatus, Oreochromis mossambica, Esomus danricus, Oryzias melastigma, Puntius sophore, P. ticto, Rasbora daniconius, R. elegans, Aplocheilus panchax, and Danio (B) rerio possess high-level larvivorous potentiality in nature and are recommended for malaria control in the study area. There is an increasing pressure on the fish fauna, of facing several threats, such as fishing, human interference, loss of habitat, overexploitation, pollution, siltation, trade, and diseases. Therefore, periodic survey and monitoring of fish biodiversity, demarcation of breeding sites, field level research study on the efficacy of these fishes, and public awareness on establishment of larvivorous fish ponds should be adopted as a part of the vector management approach in the endemic malarious region of Ranchi district in Jharkhand, India.

Presence and distribution of mosquito larvae predators and factors influencing their abundance along the Mara River, Kenya and Tanzania.

Among all the malaria controlling measures, biological control of mosquito larvae may be the cheapest and easiest to implement. This study investigated baseline predation of immature mosquitoes by macroinvertebrate predators along the Mara River, determined the diversity of predators and mosquito larvae habitats and the range of their adaptive capacity to water physico-chemical parameters. Between July and August 2011, sampling sites (n=39) along the Mara River were selected and investigated for the presence of macroinvertebrate predators and mosquito larvae. The selected sampling sites were geocoded and each dipped 20 times using standard mosquito larvae dipper to sample mosquito larvae, while a D-frame dip net was used to capture the macroinvertebrate predators. Water physico-chemical parameters (dissolved oxygen, temperature, pH, conductivity, salinity and turbidity) were taken in situ at access points, while hardness and alkalinity were measured titrimetically. The influence of macroinvertebrate predator occurrence was correlated with mosquito larvae and water quality parameters using Generalized Linear Model (GLM). Predators (n=297) belonging to 3 orders of Hemiptera (54.2%), Odonata (22.9%) and Coleoptera (22.9%), and mosquito larvae (n=4001) belonging to 10 species, which included An.gambiae s.l (44.9%), Culex spp. (34.8%) and An. coustani complex (13.8%), An. maculipalpis (3.6%), An. phaorensis (1.2%), An. funestus group (0.5%), An. azaniae (0.4%), An. hamoni (0.3%), An. christyi (0.3%), An. ardensis (0.08%), An. faini (0.07%), An. sergentii (0.05%) and 0.05% of Aedes mosquito larvae which were not identified to species level, due to lack of an appropriate key, were captured from different habitats along the Mara river. It was established that invasion of habitats by the macroinvertebrate predators were partially driven by the presence of mosquito larvae (p < 0.001), and the prevailing water physico-chemical parameters (DO, temperature, and turbidity, p <0.001). Understanding abiotic and biotic factors which favour mosquitoes and macroinveterbrate co-occurrence may contribute to the control of malaria.

Responses of three species of mosquito larvae to the presence of predatory dragonfly and damselfly larvae

AbstractAlthough predators have been extensively used in the biological control of mosquito larvae, their efficacy will be reduced if the larvae are able to detect and respond to their presence. This ability to detect and respond to the unseen presence of dragonfly or damselfly larvae was investigated for the larvae of three mosquito species (all Diptera: Culicidae) to see whether they either altered their rate of development or their feeding behaviour. The development of Culex quinquefasciatus Say and Culiseta longiareolata Macquart larvae was not affected by exudates from either predator, but Culex sinaiticus Kirkpatrick developed significantly slower when reared in the presence of a caged dragonfly larva and produced adults that were significantly smaller, indicating that they probably reduced feeding activity to make themselves less detectable to the predator. This only occurred when the dragonflies were fed in situ (in the presence of the mosquito larva) and not when removed for feeding, so that although this removed predator kairomones, other cues such as vibrations caused by movement of the predator may also be involved. In addition, the mosquito larvae responded to dragonfly larvae, but not to damselfly larvae. The depth of the water in which the mosquito larvae were reared had no effect on their response to the dragonfly. All three mosquito species significantly increased surface filter‐feeding, when a predator was present in the water (compared with controls where no predator was present), at the expense of bottom scraping. In Cx. sinaiticus (but not the other two species), surface filter‐feeding was greater when a dragonfly was present, compared with a damselfly. In the experimental conditions of one predator per 250 ml water, all three mosquito species were thus able to detect dragonfly and damselfly larvae (and distinguish between the two), but their response varied among species.

English

This review attempts to give an account on the recent advances on the killifish Aphanius dispar dispar as a biological control agent for mosquito larvae. Thirty six (36) articles of literature (scientific papers, technical and workshop reports) on this subject covering the period between 1980 and 2009 were reviewed. The larviciding process by using chemicals to control mosquitoes in the past resulted in a very harmful effects on the environment (bioaccumulation of DDT), resistance of mosquito vectors, destruction of non-target organisms and human health hazards. Biological control of mosquito larvae by using fish has shown many advantages over chemicals, but exogenous fishes such as Gambusia affinis may have negative effects on fishes and destroy the local habitat. Eco-friendly indigenous larvivorous fish with less harm to the environment and the local fish fauna is suitable for biological control of mosquito larvae. Furthermore, A. dispar is capable of natural and artificial reproduction to maintain a fish stock in order to eliminate mosquito larvae and protect people from many mosquito borne diseases such as malaria, dengue, rift valley fever (RVF), encephalitis and many others (Suliman, 2010). Hence, the indigenous killifish, A. dispar is found to play this role effectively and efficiently. Problems associated with its artificial breeding and fungal infection of its eggs can be further investigated. In addition to this, integrated methods of biological control should be carried out in order to reach the best targets of mosquito control. Key words: Biological control, mosquito larvae, indigenous fish, Aphanius dispar.

Development of a method for heterologous gene expression in Enterobacter amnigenus, a potential host for the biological control of mosquito larvi

An integrative plasmid containing a 1.3 kb fragment of chromosomal DNA from Enterobacter amnigenus was constructed. The Ω fragment encoding spectinomycin/streptomycin resistance was cloned into the unique BglII site of the resulting plasmid, and the interrupted fragment was transferred via plasmid pMAK705 by electroporation into E. amnigenus with a selection for spectinomycin resistance. Cointegrants were resolved to generate an E. amnigenus strain that expressed spectinomycin resistance, but grew as rapidly as the parental strain. The cloned fragment encodes a putative homologue of the proW gene of Escherichia coli that is not essential for E. amnigenus growth. The integrative plasmid is now available to introduce any heterologous DNA into the E. amnigenus chromosome, for the construction of promoter–probe vectors for the studies of gene regulation, or to construct plasmids suitable for the isolation of secretion signals. Immediate applications of this system will include the expression and secretion of crystal toxins from bacilli for the biological control of mosquito larvae infected with the bacterial host.

A Spawning Cage for Eliminating Predation on Larvae of the KillifishAphanius dispar

Abstract The killifish Aphanius dispar is an excellent candidate for use as a biological control of mosquito larvae. Although we are able to induce reproduction throughout the year, there are two major obstacles for mass production—cannibalism by adults on eggs and newly hatched fry and fungal overgrowth from uneaten food onto eggs. To solve these problems we designed a cage to suspend in the breeding tanks. Spawning adults were placed in the cages, and eggs fell to the bottom of the tanks. Fry hatched and developed in the tanks, while adults continued to spawn. A specially designed food dish placed in the cages greatly diminished spillage and the subsequent development of fungus on the bottom of the tanks. The separation of adults from eggs facilitated collection of eggs for further investigation (e.g., diameter, hatching time). The use of spawning cages to eliminate predation of larvae by adults makes the mass production of A. dispar more efficient and increases their appeal as a biological control agen...

Some environmental factors affecting the reproduction of Aphanius dispar (Rüppell, 1828)

In order to determine the suitability of thecyprinodont fish Aphanius dispar as a biologicalcontrol agent for mosquito larvae, the effects oftemperature, salinity, feeding rate and photoperiod onits reproductive condition were studied. The factorsexamined were the gonado-somatic index (GSI) and fourdistinct stages of cell maturation in the ovaries(oogonia, primary oocytes, secondary oocytes andmature ova). The fish were found to be tolerant to awide range of the examined factors. GSI's were notaffected by ambient temperatures over the range of18 °C to 37 °C. However, oocyte maturationstages increased as temperatures rose from 18 °Cto 27 °C, with mature ova first being found at thelatter temperature. No significant differences amongmaturation stages were found between27 °C–37 °C. At salinities ranging from of0 ppt to 56 ppt, no significant differences were found betweenmean GSI's, except for the two extremes of the testrange. The ovaries of fish kept in distilled watercontained primordial germ cells only. In feedingexperiments, significant differences were found onlybetween the ovaries (GSI's and oocyte maturationstages) of fish deprived of food and those fed at≥ 1% body weight per day. Regarding photoperiod,a decrease in day length from 14L:10D (the longest dayof the year) to 10L:14D (the shortest) caused adecrease in oocyte maturation stages. Fish at theintermediate level (12L:12D) still had ovariessuitable for spawning, whereas those at 10L:14D didnot. The results of this study show that limitinglevels for adequate reproductive condition were foundfor some of the factors investigated, however, rangesof the factors above these levels were relativelylarge. That Aphanius dispar's reproductivecondition may be controlled in an artificialenvironment is essential for it to be mass produced,and a prerequisite for its use in the biologicalcontrol of mosquito larvae.

Field evaluation of Tilapia zilli (Gervais) as a biological control agent for mosquito control

Abstract Tilapia zilli (Gervais), a larvivorous fish identified in the Mwea Rice Irrigation System (Kenya), was evaluated in the field to assess its potential for biological control of mosquito larvae. The study was conducted from October 1991 to April 1992 in experimental ponds constructed at Mbui-Njeru, which is one of the 36 villages in the irrigation scheme. T. zilli was found to be extremely effective in controlling mosquito breeding that persisted throughout the study period. However, the presence of vegetation and turbidity significantly reduced its efficiency in predation. The negative effects of vegetation could be averted by combining T. zilli with an herbivorous fish to control weeds. Similarly, breeding of other larvivorous organisms, including frogs, should be encouraged to enhance mosquito control efficiency. It is suggested that positive measures should be taken to deter colonization of catfish whose presence aggravates the turbidity problem and also depletes the fish population due to its substrate feeding and carnivorous behaviour.

Radiation-processed polymers as biomaterials

Ionising radiation provides a clean and controllable method of producing and modifying polymers for use as biomaterials. The present work surveys some of the recent advances in this field, with emphasis on recent achievements in this field as a result of the work done at the Bhabha Atomic Research Centre, such as a strip for the quick detection of jaundice, which involves a detecting agent encapsulated in a radiation crosslinked polymeric gel and the trapping of bacteria in radiation crosslinked polymers for biological control of mosquito larvae.

Feeding biology of Aplocheilichthys normani, Ahl, a small Cyprinodontidae from West Africa

Aplocheilichthys normani is a small Cyprinodontidae endemic in tropical Africa from Senegal to central Sudan. Analysis of the gut content of two populations from Guinea reveals that it feeds mainly on small crustaceans and chironomid larvae. Experimental investigations into its predatory capacity vis‐á‐vis the larvae of Aedes aegypti show that there is a significant difference between the daily feeding rates in adult versus subadult specimens. Moreover, significant 24 h variations were also observed. The feeding rate is also related to the stage of the larvae, i.e. the predatory capacity is greater for smaller prey. The 24h feeding rate variations show that A. normani feeds both during the daylight hours and at night, with a slightly higher predatory activity during the daylight hours. The peak in feeding activity occurs during the two hours before dark. Tests on feeding preferences show that the fish prefers, in descending order, Aedes, Anopheles and Culex larvae. Its larvivorous activity against mosquito larvae was corroborated by small‐scale field studies. We propose that this species be considered for possible use in the biological control of mosquito larvae in West Africa.

The pathogenicity of the fungus Culicinomyces to mosquito larvae in a natural field habitat.

The discovery of a new fungus pathogenic to mosquitoes, which was isolated from a laboratory colony of the mosquito Anopheles amictus hilli Woodhill & Lee at Sydney, Australia, was reported by Sweeney, Lee, Panter & Burgess (1973, Search 4 : 344–45). This organism appears promising as a candidate microbial insecticide, as it grows readily on simple artificial media without loss of pathogenicity. Mass production of conidia in submerged culture has been shown to be feasible and a study has begun to assess its potential for biological control of mosquito larvae. The genus Culicinomyces has recently been established by Couch, Romney & Rao (1974, Mycologia 66 : 374–79) for a newly discovered fungal pathogen of mosquito larvae from North Carolina, U.S.A. This fungus was described as C. clavosporus and was first recognized in circumstances similar to those which led to the Australian discovery. It is clear that the Australian fungus is congeneric with Culicinomyces , though its specific status can only be determined after a comparison of taxonomic material from the 2 localities.

Biological control of mosquito larvae.

Biological control of mosquito larvae.