Effects of temperature, pH and salinity on the infection of Leptolegnia chapmanii Seymour (Peronosporomycetes) in mosquito larvae

Diversity and Distribution of Culicidian Fauna in Urban and Rural Areas of Setif Region (North-East Algeria)

Objective: The study explored larval mosquito breeding sites in urban and rural areas from March 2021 to February 2022 in the North-East region of Algeria to provide information on larval biology and ecology of different mosquito species. Methodology: It focused on the effect of the physicochemical characteristics of the breeding sites (pH and water temperature), area, and months on the larval mosquito abundance. Diversity index and equitability were calculated for the registered mosquito species in both areas. Results: Months significantly affected the larval mosquito abundances, with a clear abundance increase from March to August 2021, and then, a clear decrease to February 2022. The interactions between rural and urban areas, water pH, and water temperature as well affected the mosquito abundance. Twelve species of Culicidae were identified and distributed in three genera: Culex, Culiseta, and Aedes. Culex pipiens was the most dominant species in rural and urban sites, with a rate of 69% and 48%, respectively. In rural site, Aedes caspius and Aedes vexans occupied the second position with value of 7-8% each. In urban sites, the second position was occupied by Culiseta longiareolata (36%) and then by Culex theileri (10%). In terms of site diversity, only one site was highly diversified in rural sites, El Hchichia (H' = 1.12 bits). In urban sites, Setif Center, Guellel an Ain Trick, had almost similar diversity with values between 1.03 and 1.04 bits. Equitability values were 0.48 in rural sites and 0.55 in urban sites. Therefore, the Culicidae species presented in these study sites are moderately balanced. Conclusion: The present study provides key tools for planning a better vector control through the information on the effect of some factors on the proliferation of mosquitoes in the urban and rural sites of the Setif region and on the Culicidae diversity and abundance.

Salt Stress Tolerance of Dark Septate Endophytes Is Independent of Melanin Accumulation

Dark septate endophytes (DSEs) represent a diverse group of root-endophytic fungi that have been isolated from plant roots in many different natural and anthropogenic ecosystems. Melanin is widespread in eukaryotic organisms and possesses various functions such as protecting human skin from UV radiation, affecting the virulence of pathogens, and playing a role in development and physiology of insects. Melanin is a distinctive feature of the cell walls of DSEs and has been thought to protect these fungi from abiotic stress. Melanin in DSEs is assumed to be synthesized via the 1,8-dihydroxynaphthalene (DHN) pathway. Its function in alleviation of salt stress is not yet known. The aims of this study were: (i) investigating the growth responses of three DSEs (Periconia macrospinosa, Cadophora sp., and Leptodontidium sp.) to salt stress, (ii) analyzing melanin production under salt stress and, (iii) testing the role of melanin in salt stress tolerance of DSEs. The study shows that the three DSE species can tolerate high salt concentrations. Melanin content increased in the hyphae of all DSEs at 100 mM salt, but decreased at 500 mM. This was not reflected in the RNA accumulation of the gene encoding scytalone dehydratase which is involved in melanin biosynthesis. The application of tricyclazole, a DHN-melanin biosynthesis inhibitor, did not affect either salt stress tolerance or the accumulation of sodium in the hyphae. In addition, melanin biosynthesis mutants of Leptodontidium sp. did not show decreased growth performance compared to the wild-type, especially not at high salt concentrations. This indicates that DSEs can live under salt stress and withstand these conditions regardless of melanin accumulation.

Compatibility between Leptolegnia chapmanii and diflubenzuron and neem oil for the control of Aedes aegypti

Leptolegnia chapmanii is pathogenic to mosquito larvae. The compatibility between L. chapmanii and two insect growth regulators (IGR), diflubenzuron and neem oil, was evaluated. L. chapmanii was grown on culture media containing different concentrations of each IGR. The mycelial growth was significantly reduced with the highest concentrations of IGR (F_6,98=268, p<0.05). However, the production of zoospores (F_6,56=0.93, p>0.05) and the larval mortality of Aedes aegypti (F_6,56=0.95, p>0.05) were not significantly different among treatments. Furthermore, the percentage of adult emergence in the presence of different concentrations of diflubenzuron or a neem formulation was determined, and the pathogenic activity of zoospores was evaluated at the concentrations that inhibit the emergence at 30, 50 and 90%. The pathogenicity of zoospores was not significantly different among treatments (F_6,14=0.54, p>0.05), and the larval mortalities were above 90% in all cases.

Leptolegnia chapmanii como alternativa biológica para el control de Aedes aegypti

Leptolegnia chapmanii is a facultative pathogen of many species of mosquitoes, among which species of the genus Aedes, Culex and Anopheles stand out for their medical and sanitary importance. The potential of L. chapmanii as an alternative to control lies in its virulence, pathogenicity and specificity against the larval stages of mosquitoes, and because of its harmlessness to non-target species such as fish and amphibians, among others. The natural presence of L. chapmanii had been reported in Argentina, Brazil and the United States. Its presence is possible in other countries throughout the American continent. The development of protocols to produce, formulate, store and apply products based on this microorganism is one of the objectives proposed for the group of Entomopathogenic Fungi at the Centro de Estudios Parasitológicos y de Vectores, Universidad Nacional de La Plata. The efficacy of L. chapmanii as controller is affected by external factors such as temperature, pH, salinity and radiation among others. The process of transfer from the research centers to industry implies many phases. In this way, our project with L. chapmanii is in an initial phase, where we are working on a laboratory scale in proof of concept. We hope to begin soon with the efficacy, efficiency, stability and ecotoxicological safety tests, at the laboratory, semi-field and field scale.

Quantifying the Influence of Larval Density on Disease Transmission Indices in Culex quinquefasciatus, the Major African Vector of Filariasis

Larval crowding is one of the abiotic factors affecting biological fitness in mosquitoes. This study aims at elucidating, quantitatively, the influence of more larval crowding on aspects of fitness in Culex quinquefasciatus mosquito. To this end, day-old larvae of the species were reared in 4 density regimens equivalent to 1 larva in 1.25, 2.5, 5, and 10 mL of distilled water. Developmental indices, adult fitness indices, and accumulation and utilisation of teneral reserves for metamorphosis were determined at these density regimens. The results revealed varying significant negative effects of larval density on all fitness indices measured for the species. The study also revealed high utilisation of teneral reserves for metamorphosis at high larval densities. The information generated will be useful in making informed-decisions in allocating scare resources for vector control, although field trials are advocated to establish these laboratory findings.

Water source most suitable for rearing a sensitive malaria vector, Anopheles funestus in the laboratory

Background:  The insecticide susceptibility status of Anopheles funestus, one of the main malaria vectors in the Afrotropical regions, remains under-studied due to the difficulty of working with this mosquito species. Collecting their larvae in natural breeding sites, rearing and maintaining them in normal laboratory conditions have been a difficult task. Forced-egg laying technique has been a very good tool to generate eggs from adult mosquitoes collected from the wild but rearing these eggs to obtain satisfying portion as adults has always been the problem. In this study, we optimized the development of mosquito species larvae under standard laboratory conditions for desired production of adult mosquitoes that can be useful for insecticide susceptibility tests.

Methods:  A forced-egg laying technique was used to obtain eggs from gravid female Anopheles funestus collected from Kpome locality in Benin. Eggs were reared in three different water samples (water from the borehole, and two mineral water namely FIFA and Possotômè) and larvae were fed with TetraMin baby fish food. The physico-chemical parameters of the waters were investigated prior to use for egg incubation (introduction of eggs’ batches into water).

Results: In contrast to mineral water that had no contamination, the borehole water source was contaminated with lead (2.5mg/L) and nitrate (118.8mg/L). Egg hatching rates ranged as 91.9 ± 4.4%, 89.1 ± 2.5% and 87.9 ± 2.6% in FIFA, Possotômè and borehole water respectively. High emergence of larvae to adult mosquitoes was recorded as in FIFA (74.3%) and Possotômè (79.5%) water. No adult mosquito was obtained from larvae reared in borehole water.

Conclusions: This study gave insight on the water sources that could be good for rearing to mass produce An. funestus in the laboratory. More analysis with other local mineral water sources in our environments could be considered in the future, hopefully giving better outputs.

Water source most suitable for rearing a sensitive malaria vector, Anopheles funestus in the laboratory

Background:  The insecticide susceptibility status ofAnopheles funestus,one of the main malaria vectors in the Afrotropical regions, remains under-studied due to the difficulty of working with this mosquito species. Collecting their larvae in natural breeding sites, rearing and maintaining them in normal laboratory conditions have been a difficult task. Forced-egg laying technique has been a very good tool to generate eggs from adult mosquitoes collected from the wild but rearing these eggs to obtain satisfying portion as adults has always been the problem. In this study, we optimized the development of mosquito species larvae under standard laboratory conditions for desired production of adult mosquitoes that can be useful for insecticide susceptibility tests.Methods: A forced-egg laying technique was used to obtain eggs from gravid femaleAnopheles funestuscollected from Kpome locality in Benin. Eggs were reared in three different water samples (water from the borehole,and two mineral water namely FIFA and Possotômè) and larvae were fed with TetraMin baby fish food. The physico-chemical parameters of the waters were investigated prior to use for egg incubation.Results:In contrast to mineral water that had no contamination, the borehole water source was contaminated with lead (2.5mg/L) and nitrate (118.8mg/L). Egg hatching rates ranged as 91.9 ± 4.4%, 89.1 ± 2.5% and 87.9 ± 2.6% in FIFA, Possotômè and borehole water respectively. High emergence of larvae to adult mosquitoes was recorded as in FIFA (74.3%) and Possotômè(79.5%) water. No adult mosquito was obtained from larvae reared in borehole water.Conclusions:This study gave insight on the water sources that could be good for rearing to mass produceAn. funestusin the laboratory. More analysis with other local mineral water sources in our environments could be considered in the future, hopefully giving better outputs.

Larval Habitat Substrates Could Affect the Biology and Vectorial Capacity of Culex quinquefasciatus (Diptera: Culicidae)

Culex quinquefasciatus Say is an important disease vector throughout much of the world. Experiments were conducted to determine the effects of different larval habitat substrates on the fitness and biting efficiency of Cx. quinquefasciatus adults. Our findings indicate that the development time (egg to adult) of larvae reared in irrigation water was 8.63 d while that of larvae reared in distilled water was 17.10 d (Effect size = 0.95). However, the rate of adult emergence was similar for all the tested treatments. Furthermore, the mean weight of an egg raft varied between larval habitats: distilled water (1.83 mg), rainfall water (1.25 mg), irrigation water (1.52 mg), and sewerage water (2.52 mg) (Effect size = 0.91). But, the fecundity (eggs per female) and hatchability (%) were statistically similar in all the rearing mediums (Effect size = 0.79). Longevity of females in all the tested populations did not differ significantly (Effect size = 0.91). The mean relative growth rates of larvae reared in tap water (0.80) and distilled water (0.86) habitats were lower than growth rates in all other rearing habitats (Effect size = 0.96). The intrinsic rate of natural increase in tap water (0.27) and irrigation water (0.35) was significantly higher than that in distilled water (0.09) and sewerage water (0.16) (Effect size = 0.84). Adults reared in rain water had the highest biting efficiency among all the tested populations. These results provide useful information for the management of Cx. quinquefasciatus.

Leptolegnia chapmanii (Straminipila: Peronosporomycetes) as a future biorational tool for the control of Aedes aegypti (L.)

The aim of the present review is to summarize the current knowledge about Leptolegnia chapmanii as a pathogen of mosquito larvae. To this end, we present data on its identification, distribution, host range and effects on non-target organisms, effects of environmental factors, in vitro growth, release and persistence in anthropic environments, and effect combined with other insecticides. The data presented allow confirming its potential as a biocontrol agent.

Effect of ultraviolet-A radiation on the production of Leptolegnia chapmanii (Saprolegniales: Saprolegniaceae) zoospores on dead Aedes aegypti (Diptera: Culicidae) larvae and their larvicidal activity

Impact of UV-radiation in entomopathogens in aquatic environments remains little investigated. The present study reports on the effect of UV-A on the larvicidal activity of Leptolegnia chapmanii zoospores in Aedes aegypti; on the production of zoospores in larvae killed by the pathogen and then exposed to UV-A; and on the activity of these zoospores against healthy larvae. Whereas the virulence of free zoospores in A. aegypti larvae was affected by a UV-A exposure time longer than 10min, production of zoospores in larvae and their virulence were not hampered at a maximal 8h exposure of dead larvae to UV-A. Findings suggest that dead larvae and zoosporangia provide a certain protection to zoospores against UV-A and emphasize the susceptibility of free encysted zoospores to such radiation.

Effects of Two Salts Compounds on Mycelial Growth, Sporulation, and Spore Germination of Six Isolates of Botrytis cinerea in the Western North of Algeria

Six isolates of Botrytis cinerea were isolated from leaves and stems of different tomato varieties taken from four areas in the northwest of Algeria where tomato is mostly grown in greenhouses and high tunnels. The purpose of this research was to determine the effect of two salts, NaCl and CaCl2, on three stages of Botrytis cinerea's life cycle. All isolates tested were stimulated in 50 to 150 ppm; NaCl was the most effective treatment to increase mycelial growth at two tested concentrations. However, at 300 ppm concentration, CaCl2 completely inhibited the growth of mycelium; they reach 34.78% for the isolate TR46 and 26.72% for isolate F27. The sodium and calcium salts stimulated conidia production in liquid culture. We noticed that the effect of calcium chloride on sporulation was average while sodium chloride. In the medium containing 50 ppm, calcium chloride and sodium chloride increased the germination capacity of most isolates compared with the control. Other calcium salts, at 100 or 300 ppm, decreased the germination percentage of the conidia. With the exception of sodium salts, the inhibitions of germination reduce at 150 or 300 compared with the control. Conidial germination was slightly inhibited by sodium chloride only when the concentration was over 300 ppm.

A simple method for the detection of Leptolegnia chapmanii from infected Aedes aegypti larvae

Significant progress in developing Leptolegnia chapmanii as a biological control agent against mosquitoes will be accelerated by improved and simpler methods to detect and to isolate this virulent and rapidly lethal watermold from field-collected mosquito larvae. To date, however, this oomycete has remained understudied and little used. This study presents a simplified method to detect Leptolegnia in infected Aedes aegypti larvae. The development of L. chapmanii inside mosquitoes is easily monitored when pathogen-treated larvae are quasi-immobilized for an initial 48 h in the water film on plates of water agar amended with antibiotic (chloramphenicol, 0.5–1 g/L) and fungicide (thiabendazole, 4–8 g/L) and then transferred to a larger volume of water for an additional 48 h. Surprisingly, chloramphenicol stimulated oosporogenesis by L. chapmanii. The method permits processing of large numbers of A. aegypti and other culicid larvae and is useful for both obtaining new strains and also monitoring the efficacy of L. chapmanii during field tests.

The sublethal effects of the entomopathic fungus Leptolegnia chapmanii on some biological parameters of the dengue vector Aedes aegypti

The mosquito Aedes aegypti (L.) (Diptera: Culicidae) is the primary vector of dengue in the Americas. The use of chemical insecticides is recommended during outbreaks of dengue in order to reduce the number of adult mosquitoes; however, because Ae. aegypti is highly synanthropic, the use of insecticides in densely populated areas is a dangerous practice. Leptolegnia chapmanii Seymour (Straminipila: Peronosporomycetes) is an entomopathogenic microorganism that has demonstrated marked pathogenicity toward the larvae of a number of mosquito species, with little or no effect on non-target insects. Therefore, the purpose of this study was to determine the sublethal effects of L. chapmanii on fecundity, number of gonotrophic cycles, fertility, and relationship between wing length and fecundity in Ae. aegypti females. Ae. aegypti females that survived infection with L. chapmanii laid fewer eggs, had a smaller number of gonotrophic cycles, had shorter wings, and were less fertile than controls. This is the first study on the sublethal effects experienced by specimens of Ae. aegypti that survived infection with zoospores of L. chapmanii. Although field studies should be carried out, the results obtained in this study are encouraging because the high and rapid larval mortality caused by L. chapmanii coupled with the reduction of reproductive capacity in Ae. aegypti females seem to cause a significant reduction in the number of adults in the mid and long term, thereby reducing the health risks associated with Ae. aegypti.