Stephensi Larvae Research Articles

Laboratory and semi-field evaluations on lethal and residual effects of temephos and pyriproxyfen insecticides to control malaria mosquito larvae, Anopheles stephensi Liston

BackgroundThe application of insecticides against vector mosquito larvae is a crucial step to control human malaria. Insecticide resistance is a major impediment to vector control strategies. The main aim of this study was to conduct laboratory and semi-field evaluations on lethal and residual effects of temephos and pyriproxyfen insecticides against malaria mosquito larvae, Anopheles stephensi.MethodsBoth susceptibility test and residual bioassay were performed to assess the lethal concentrations of each insecticide on 50% (LC50) of the IV instars larval populations and their activity periods according to standard protocols of WHO. Nine and eleven different concentrations with two sets of control in each case were applied for temephos and pyriproxyfen, respectively. Data were analyzed using probit analysis and SPSS software.ResultsThe LC50 and LC90 for temephos and pyriproxyfen under laboratory conditions were 0.4 and 0.63, and 1.69 × 10-4 and 4.036 × 10-4 ppm, respectively. Although the field strain of An. stephensi larvae was completely susceptible to pyriproxyfen, there was noticeable resistance (8% mortality at the diagnostic dose) to temephos in Nikshahr County, Southeast Iran. This is the first report of resistance to temephos for this malaria main vector in Iran. Depending on the applied variable doses, the residual effects of temephos and pyriproxyfen under semi-field conditions lasted maximally for 3 and 10 weeks, respectively.ConclusionThe high lethal and residual effects of pyriproxyfen on mosquito larvae confer an unprecedented opportunity in vector control operations leading to elimination of malaria in Iran.

Interspecific competition between larval stages of Aedes aegypti and Anopheles stephensi.

Interspecific competition occurs between members of two or more different species and can often have an influence on mosquito populations. Both Aedes aegypti and Anopheles stepehensi are container breeding mosquitoes and co-exist which may result in larval competition. In this study, interspecific competition between the above two species has been monitored under the laboratory conditions. Three sets of experiments were conducted with different stages of Ae. aegypti and An. stephensi larvae. First two experiments were set up with I/II instar and III/IV instar larvae of Ae. aegypti and An. stephensi respectively in the ratios of 20:20, 20:40 and 40:20 in plastic bowls. For third set of experiment 20 IV instar larvae of Ae. aegypti were put with equal number of I instar larvae of An. stephensi. In the presence of food, 12.5-15 % mortality was recorded in I/II stage larvae of Ae. aegypti while in An. stephensi mortality ranged from 21-55%. Pupation commenced from Day 6 onwards in Ae. aegypti while in An. stephensi it commenced from Day 11 onwards. In the absence of food, there was no pupation in both the species but Ae. aegypti survived up to longer duration (7.5-18.5 days with 50% mortality) in comparison to An. stephensi (2-7 days with 50% mortality). When younger stages of An. stephensi (I/II) were put together with older stages of Ae. aegypti (III/IV) in the presence of food, pupation was completed in 85% Ae. aegypti population while there was 100% mortality in An. stephensi population. The better survival and development of Ae. aegypti than An. stephensi under the same conditions exhibits interspecies competition showing competitive advantage of Ae. aegypti over An. stephensi. Further research is required to have a thorough understanding of the interaction between these two container inhabiting mosquito species in the nature.

Adenosine Triphosphate-Binding Cassette Transporters Are Not Involved In the Detoxification of Azadirachta indica Extracts In Anopheles stephensi Larvae.

Detoxifying pathways of mosquitoes against the neem (Azadirachta indica) extracts are still unclear. The aim of the present study was to investigate the role of adenosine triphosphate-binding cassette (ABC) transporters in this process in Anopheles stephensi, one of the main malaria vectors in southern Asia. Third-stage larvae of An. stephensi were fed with fish food alone or in combination with neem extract at 0.5%, 1%, 5%, and 10%. Six ABC-transporter genes from 3 different subfamilies (B, C, and G) were analyzed to assess their relative expression compared with controls. A bioassay was also performed to assess larval mortality rate at different concentrations and in combination with verapamil, an ABC-transporter inhibitor. No significant variation in the expression levels of any transporter belonging to the B, C, and G subfamilies was detected. Furthermore, the use of verapamil did not induce an increase in mortality at any of the tested neem extract concentrations, indicating that ABC transporters are not involved in the detoxification of neem extracts in An. stephensi larvae.

Lagenaria siceraria - synthesised ZnO NPs - a valuable green route to control the malaria vector Anopheles stephensi.

Malaria is a dangerous disease affecting humans and animals in tropical and subtropical areas worldwide. According to recent estimates, 3.2 billion people are at risk of malaria. Many drugs are in practices to control this disease and their vectors. Eco-friendly control tools are needed to fight vectors of this important disease. Nanotechnology is playing a key role in the fight against many public health emergencies. In the present study, Lagenaria siceraria aqueous peel extract was used to prepare zinc oxide nanoparticles (ZnO NPs), then tested on Anopheles stephensi eggs, larvae and pupae. The L. siceraria-synthesised ZnO NPs were characterized additionally by FTIR, AFM, XRD, UV-Vis spectroscopy, EDX, and SEM spectroscopy The ovicidal, larvicidal, pupicidal and repellent activities of L. siceraria and green-synthesised ZnO NPs were analysed on A. stephensi. The potential mechanism of action of ZnO NPs was studied investigating the changes in various enzyme activities in A. stephensi IV instar larvae. Furthermore, the smoke toxicity of L. siceraria-based cones against A. stephensi evoked higher mortality if compared with the control. Overall, the present study concluded that L. siceraria peel extract and its mediated green synthesised ZnO NPs represent a valuable green option to manage against malaria vectors.

Larvicidal Activity of Methanol and Chloroform Extract of Swertia celiata against Three Mosquito Vectors

Background: Mosquitoes are an important public health concern as they spread life-threatening diseases such as malaria, filaria, Japanese encephalitis, dengue fever, chikungunya, and yellow fever. In the last decades, synthetic insecticides were extensively used for the control of these vector-borne diseases but it also reported the detrimental side-effects in human beings and pet animals. To overcome the side effects, plants-derived secondary metabolites were screened and tested for insecticidal properties. The present study deals with the insecticidal activity of chloroform and methanol extracts of Swertia celiata leaves against Culex quenquifasciatus, Aedes aegypti, and Anopheles stephensi larvae. Method: The S. celiata leaves were subjected to chloroform and methanol with 1:3 (Weight/ Volume) ratio and the extracted solvent was dried using rotary vacuum evaporator. The larvicidal activity of the extract was tested using WHO method and LC50 and LC90 were evaluated by probit analysis. Results: The LC50 value of chloroform extract of S. celiata was found to be 65.288, 67.406 and 71.608 ppm whereas LC90 was 184.721, 186.582 and 192.497 ppm against C. quinquefasciatus, Ae. aegypti and A. stephensi, respectively. The methanolic extract was also found potent; LC50 was 91.503, 101.574 and 99.104 ppm whereas LC90 was 230.823, 271.927 and 234.257 ppm against C. quinquefasciatus, Ae. aegypti and A. stephensi, respectively. Both chloroform and methanol extract were found significantly lethal to the tested mosquito vectors. Conclusion: Taken results together, chloroform extract showed higher toxicity as compared to methanolic extract against all the tested species. The study clearly revealed that S. ciliata extract or bioactive compounds can be used as an alternative to synthetic insecticides.

Strong larvicidal potential of silver nanoparticles (AgNPs) synthesized using Holarrhena antidysenterica (L.) Wall. bark extract against malarial vector, Anopheles stephensi Liston

Abstract The present study highlights the strong larvicidal potential of silver nanoparticles (AgNPs) synthesized using bark extract of Holarrhena antidysenterica against third instar larvae of Anopheles stephensi over the other bark extract prepared in chloroform, hexane, ethyl acetate, methanol, aqueous and acetone individually. AgNPs were prepared by mixing of 90 ml of silver nitrate (AgNO3) with 10 ml of aqueous bark extract of H. antidysenterica. Optimization of various physical parameters such as temperature, pH, time duration and AgNO3 concentrations was done and 1 mM of AgNO3, 7.5 pH, 50 ± 2 °C temp and time 120 min proved optimum for best synthesis of AgNPs. Characterized of AgNPs was done by ultraviolet-visible spectroscopy (UV–vis), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). XRD pattern of such AgNPs revealed characteristics Bragg’s reflection peaks at (38.34) 111, (44.54) 200, (64.36) 220 and (76.9) 311 lattice planes indicating the crystalline nature of biologically synthesized AgNPs. FT-IR analysis of AgNPs exhibited the presence of functional groups of various compounds including phenols, alcohols, amine, amide which were responsible for the reduction and capping of AgNPs. The FE-SEM and TEM images showed that most of the AgNPs were spherical, hexagonal and triangular in shape varying from 40 to 60 nm in size. Larvicidal activity of these AgNPs and bark extracts prepared in different solvents such as hexane, ethyl acetate, methanol, water and chloroform were tested separately against the A. stephensi larvae for 24 h. Maximum larval mortality was seen with bark extract synthesized AgNPs having LC50 and LC90 value of 2.672 ppm and 4.482 ppm, respectively compared to chloroform, hexane, ethyl acetate, methanol, water and acetone bark extracts where the LC50 values were 3.0, 31.56, 41.92, 96.40, 121.53 and 1.91E3 ppm, respectively. Incidentally, AgNPs proved non-toxic against the non-target organism, Mesocyclops thermocyclopoides. GC–MS analysis of bark extract identified 41 compounds having a range of activities which might have helped in the bio-reduction of AgNPs. These AgNPs have tremendous applications in pharmaceutical and biomedical industries such as cancer therapies, targeted drug delivery, as antiseptic agents and as an imaging agent.

Biosynthesis of Pyramidical Nanosilver Using Andrographis paniculata (Burm.f.) and its Efficacy against Anopheles stephensi (Liston) Larvae in Laboratory

Biosynthesis of Pyramidical Nanosilver Using Andrographis paniculata (Burm.f.) and its Efficacy against Anopheles stephensi (Liston) Larvae in Laboratory

Fitness cost of malaria vector Anopheles stephensi induced with larvicidal and nutritional stress

Our study focused on how externally applied single or multiple stressors alter the fitness of early IV instar Anopheles stephensi larvae by inducing various larval stressors such as starvation and sublethal doses (LC10, LC25 and LC50 for 24, 48 and 72h) of various conventional and biorational larvicides. Larval stress specific response was observed in terms of their nutritional (glycogen, sugar, lipid and protein) and biochemical (DNA) status compared with respective control group which were found to be significantly (P<0.05) altered. Nutrition depletion index was found to be concentration dependent depicting maximum reduction at LC50 concentration with all applied larvicides. Significant (P<0.05) reduction in DNA level was observed only with neem oil (10–23%) and Bti (21–23%) treatments. DNA damage was further evidenced by generating RAPD profiles that revealed variations in band intensities along with addition or deletion of few band in stress induced larvae. Overall, our results depicted that An. stephensi larvae may possibly tolerate the induced stress within certain limits by modifying their nutritional and biochemical levels, which may occur at a significant fitness cost.

Phytochemical Properties and Insecticidal Potential of Volatile Oils from Tanacetum persicum and Achillea kellalensis Against Two Medically Important Mosquitoes

Mosquitoes play a predominant role in the transmission of parasitic and viral diseases which are today among the greatest health problems in the world. Currently, synthetic insecticides are the most commonly used compounds for the control of larval mosquitoes. Nevertheless, the continuous and indiscriminate use of synthetic larvicides has also induced adverse effects. Essential oils obtained from plants can be an alternative to synthetic insecticides because they are highly effective, safe, and environmentally acceptable. In this study, the larval stage of Anopheles stephensi, and Culex quinnquefaciatus were exposed to serial concentrations of essential oils from Tanacetum persicum and Achillea kellalensis for 24 h under laboratory condition. In addition, the chemical composition of essential oils were determined and identified by Gas chromatography (GC) and GC-mass spectrometry (MS) analysis. Both plant oils exerted significant larvicidal activity against An. stephensi and Cx. quinquefasciatus. The LC values of T. persicum and A. kellalensis against An. stephensi larvae were 48.64 and 35.42 ppm, and for Cx. quinquefasciatus were 28.53 and 21.79 ppm, respectively. In A. kellalensis, 36 components were identified, representing 97.26 % of the oil, of which βocimene (17.72 %), linalyl acetate (15.98 %), linalool (10.83 %) and α-pinene (10.3 %) were found to be the major constituents. Twenty components were identified in the oil of T. persicum, making up 89.60 % of total composition. The main constituents were Borneol (26.4 %), chrysanthenone (16.48 %), bornyl acetate (10.68 %) and βfarnesene (9.89 %). Our results suggested that both examined oils may be explored as a natural larvicide to control vector mosquitoes.

Dynamics of Plasmodium vivax sporogony in wild Anopheles stephensi in a malaria-endemic region of Western India

BackgroundIn global efforts to track mosquito infectivity and parasite elimination, controlled mosquito-feeding experiments can help in understanding the dynamics of parasite development in vectors. Anopheles stephensi is often accepted as the major urban malaria vector that transmits Plasmodium in Goa and elsewhere in South Asia. However, much needs to be learned about the interactions of Plasmodium vivax with An. stephensi. As a component of the US NIH International Center of Excellence for Malaria Research (ICEMR) for Malaria Evolution in South Asia (MESA), a series of membrane-feeding experiments with wild An. stephensi and P. vivax were carried out to better understand this vector-parasite interaction.MethodsWild An. stephensi larvae and pupae were collected from curing water in construction sites in the city of Ponda, Goa, India. The larvae and pupae were reared at the MESA ICEMR insectary within the National Institute of Malaria Research (NIMR) field unit in Goa until they emerged into adult mosquitoes. Blood for membrane-feeding experiments was obtained from malaria patients at the local Goa Medical College and Hospital who volunteered for the study. Parasites were counted by Miller reticule technique and correlation between gametocytaemia/parasitaemia and successful mosquito infection was studied.ResultsA weak but significant correlation was found between patient blood gametocytaemia/parasitaemia and mosquito oocyst load. No correlation was observed between gametocytaemia/parasitaemia and oocyst infection rates, and between gametocyte sex ratio and oocyst load. When it came to development of the parasite in the mosquito, a strong positive correlation was observed between oocyst midgut levels and sporozoite infection rates, and between oocyst levels and salivary gland sporozoite loads. Kinetic studies showed that sporozoites appeared in the salivary gland as early as day 7, post-infection.ConclusionsThis is the first study in India to carry out membrane-feeding experiments with wild An. stephensi and P. vivax. A wide range of mosquito infection loads and infection rates were observed, pointing to a strong interplay between parasite, vector and human factors. Most of the present observations are in agreement with feeding experiments conducted with P. vivax elsewhere in the world.

Insecticide susceptibility of Anopheles mosquitoes changes in response to variations in the larval environment

Insecticide resistance threatens the success achieved through vector control in reducing the burden of malaria. An understanding of insecticide resistance mechanisms would help to develop novel tools and strategies to restore the efficacy of insecticides. Although we have substantially improved our understanding of the genetic basis of insecticide resistance over the last decade, we still know little of how environmental variations influence the mosquito phenotype. Here, we measured how variations in larval rearing conditions change the insecticide susceptibility phenotype of adult Anopheles mosquitoes. Anopheles gambiae and A. stephensi larvae were bred under different combinations of temperature, population density and nutrition, and the emerging adults were exposed to permethrin. Mosquitoes bred under different conditions showed considerable changes in mortality rates and body weight, with nutrition being the major factor. Weight is a strong predictor of insecticide susceptibility and bigger mosquitoes are more likely to survive insecticide treatment. The changes can be substantial, such that the same mosquito colony may be considered fully susceptible or highly resistant when judged by World Health Organization discriminatory concentrations. The results shown here emphasise the importance of the environmental background in developing insecticide resistance phenotypes, and caution for the interpretation of data generated by insecticide susceptibility assays.

Potential larvicidal activity of silver nanohybrids synthesized using leaf extracts of Cleistanthus collinus (Roxb.) Benth. ex Hook.f. and Strychnos nux-vomica L. nux-vomica against dengue, Chikungunya and Zika vectors

This study focused on green engineering of stable metallic silver nanohybrids (AgNPs) using Cleistanthus collinus (Cc) and Strychnos nux-vomica (Sn) plant leaf extracts via microwave irradiation and its bioinsecticidal activity against the mosquito vectors and antimicrobial efficacy against clinically isolated human pathogens. Engineered silver nanohybrids (CcAgNPs and SnAgNPs) were characterized by UV-vis spectroscopy, Fourier Transform Infra-red spectroscopy (FTIR), X-ray diffraction spectroscopy (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Energy-dispersive X-ray spectroscopy (EDX) analysis. FTIR results showed the role of alcohols, amines, alkanes, and amides in the bioreduction, capping and stabilization of synthesized silver nanoparticles. The XRD analysis confirmed the crystalline structure of the synthesized silver nanohybrids. FESEM results displayed the shape as well as size of the engineered CcAgNPs and SnAgNPs. Interestingly, the synthesized CcAgNPs was found to be triangular and pentagonal shape with 66.27–75.09 nm size and the synthesized SnAgNPs showed irregular, spherical and round shape with 54.45–60.84 nm size. The existence of silver ion signals on engineered nanohybrids at 2.8 to 4 KeV was established by EDX analysis. Further, both C. collinus and S. nux-vomica leaf extracts and engineered CcAgNPs and SnAgNPs showed highest larvicidal activity against Anopheles stephensi and Aedes aegypti fourth instar larvae. The maximum mortality rate (100%) for CcAgNPs was observed at 20 mg/l and 25 mg/l for A. aegypti and A. stephensi vectors respectively, while highest percent of mortality for SnAgNPs was noticed in both A. aegypti and A. stephensi at 25 mg/l. The LC50 dose for CcAgNPs towards A. stephensi and A. aegypti mosquito vectors noticed were 11.05 and 11.38 mg/l, respectively, whereas the LC50 data for SnAgNPs obtained was 8.82 and 7.75 mg/l for A. stephensiand A. aegypti, respectively. The larvicidal activity was positively correlated with the engineered AgNPs exposure. Both CcAgNPs and SnAgNPs found to be effective antimicrobial agent against six human microbial pathogens and these nanohybrids may be considered as effective antibacterial nanodrug. The results strongly suggest that C. collinus and S. nux-vomica plant extracts derived silver nanohybrids can be applied as a natural biolarvicidal compound to vector-control strategy as non-toxic and eco-friendly approach to prohibit Zika, Chikungunya and dengue fever in the future.

Solution Combustion Synthesis of Hierarchically Structured V2O5 Nanoflakes: Efficacy Against Plasmodium falciparum, Plasmodium berghei and the Malaria Vector Anopheles stephensi

The effective prevention and treatment of malaria still represent a major public health challenge. Here, the solution combustion method was used for the synthesis of hierarchically structured V2O5 nanoflakes. The toxicity of V2O5 nanoflakes was evaluated on the malaria vector Anopheles stephensi and on the malaria parasites Plasmodium falciparum and P. berghei, relying to in vitro and in vivo assays. V2O5 nanoflakes were examined by various techniques, including powder X-ray diffraction, field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (XRD), and high resolution transmission electron microscopy (HR-TEM). LC50 of V2O5 nanoflakes against A. stephensi larvae and pupae were 1.936 ppm (larva I), 3.606 ppm (II), 4.750 ppm (III), 6.636 ppm (IV), and 8.876 ppm (pupae). Furthermore, the antiplasmodial activity of V2O5 nanoflakes was evaluated against chloroquine-resistant (CQ-r) and CQ-sensitive (CQ-s) strains of P. falciparum. IC50 of V2O5 nanoflakes were 84.54 μg/ml (CQ-s) and 88.17 μg/ml (CQ-r). In vivo antiplasmodial experiments conducted on P. berghei infecting albino mice showed moderate activity of V2O5 nanoflakes, if compared to chloroquine. Overall, our results highlighted the promising potential of the solution combustion method for the synthesis of hierarchically structured V2O5 nanoflakes, which showed really high efficacy as mosquito larvicides and pupicides.

Phytochemical Profile and Mosquito Larvicidal Activity of the Essential Oil from Aerial Parts of Satureja bachtiarica Bunge Against Malaria and Lymphatic Filariasis Vectors

Mosquitoes play an important role in transmission of large number of diseases including malaria, filariasis and arboviral diseases. Increasing application of synthetic insecticides may be resulted in resistant to insecticides. Furthermore, it may have adverse effects on the environment and human health. Currently, one of the most effective alternative approaches under the biological control programs is using of natural larvicidal agents derived from plants. The larvicidal properties of essential oil obtained from the aerial parts of an indigenous plant, Satureja bachtiarica was evaluated against two mosquito vector, Anopheles stephensi and Culex quinquefasciatus. In addition, the analysis of essential oil was investigated by Gas chromatography-Mass spectrometry (GC-MS). Forty-one compounds, representing 98.42% of the essential oils have been identified. The main constituents were carvacrol (22.66%), p-cymene (15.89%), borneol (14.05 %), 1,8-cineole (10.45%) and thymol (7.27%). Five different concentrations of essential oil were evaluated against the late 3rd and early 4th instars larvae of An. stephensi and Cx. quinquefasciatus. The LC50 and LC90 values against An. stephensi larvae were 24.27 and 54.24 ppm and for Cx. quinquefasciatus were 44.96 and 114.45 ppm after 24 hours of exposure, respectively. In conclusion, results of study clearly indicated that the essential oils of S. bachtiarica possessed remarkable larvicidal properties and could serve as an alternative to synthetic insecticides for control of mosquito larvae.

Differential Pathogenicity of Metarhizium Blastospores and Conidia Against Larvae of Three Mosquito Species.

Biorational insecticides are being increasingly used in integrated pest management programs. In laboratory bioassays, the pathogenicity of blastospores and conidia of the entomopathogenic fungus Metarhizium brunneum ARSEF 4556 was evaluated against larvae of three mosquito species. Three propagule concentrations (1 × 106, 1 × 107, and 1 × 108 spores ml - 1) were used in the bioassays. Results showed that Aedes aegypti had lower survival rates when exposed to blastospores than when exposed to conidia, whereas the converse was true for Culex quinquefasciatus larvae. Anopheles stephensi larvae survival rates were similar when exposed to blastospores and conidia, except at the higher doses, where blastospores were more virulent. Several assays showed little difference in mortalities when using either 1 × 107 or 1 × 108 spores ml - 1, suggesting a threshold above which no higher control levels or economic benefit would be achieved. When tested at the lowest dose, the LT50 of Cx. quinquefasciatus using blastospores, wet conidia, and dry conidia was 3.2, 1.9, and 4.4 d, respectively. The LT50 of Ae. aegypti using blastospores, wet conidia, and dry conidia was 1.3, 3.3, and 6.2 d, respectively. The LT50 of An. stephensi using blastospores, wet conidia, and dry conidia was 2.0, 1.9, and 2.1 d, respectively. These observations suggest that for optimized control, two different formulations of the fungus may be needed when treating areas where there are mixed populations of Aedes, Anopheles, and Culex.

The choreography of the chemical defensome response to insecticide stress: insights into the Anopheles stephensi transcriptome using RNA-Seq

Animals respond to chemical stress with an array of gene families and pathways termed “chemical defensome”. In arthropods, despite many defensome genes have been detected, how their activation is arranged during toxic exposure remains poorly understood. Here, we sequenced the transcriptome of Anopheles stephensi larvae exposed for six, 24 and 48 hours to the LD50 dose of the insecticide permethrin to monitor transcriptional changes of defensome genes across time. A total of 177 genes involved in insecticide defense were differentially expressed (DE) in at least one time-point, including genes encoding for Phase 0, I, II, III and antioxidant enzymes and for Heat Shock and Cuticular Proteins. Three major patterns emerged throughout time. First, most of DE genes were down-regulated at all time-points, suggesting a reallocation of energetic resources during insecticide stress. Second, single genes and clusters of genes turn off and on from six to 48 hours of treatment, showing a modulated response across time. Third, the number of up-regulated genes peaked at six hours and then decreased during exposure. Our results give a first picture of how defensome gene families respond against toxicants and provide a valuable resource for understanding how defensome genes work together during insecticide stress.

Study of histoarchitectural changes in Anopheles stephensi larvae following exposure to Eucalyptus globulus and Aloe vera oils

Chemical-based insecticides/larvicides pose a great threat to humans. The present study describes the histopathological changes in Anopheles stephensi Liston (Diptera: Culicidae) larvae after exposure to two essential oils, i.e. Eucalyptus globulus and Aloe vera. The exposure of 4th instar larvae of An. stephensi to 90 ppm of E. globulus and 550 ppm of A. vera oils resulted in various histological alterations in organs of the head regions like disintegration of the brain and other structures, disorganization in the imaginal buds of the antennae, complete disappearance of the optic lobes, and total disruption of the inner and outer retractor muscles of the brush as compared to the control larvae. Oil-exposed larvae also exhibited diversifications in gastric ceca, disintegration of the midgut epithelium layer, rifts in microvilli, and disappearance or reduction of fat bodies as well as the epithelium layer of the hindgut. Such pathological changes restrict the larvae's ability to perform various functions, leading to their death.

Fly ash-based water dispersible powder formulation of Bacillus thuringiensis var. israelensis: Development & laboratory evaluation against mosquito immatures.

Background & objectives:Bacillus thuringiensis var. israelensis (Bti) formulations are presently being used for insect control. In this study, a water dispersible powder (WDP) formulation using fly ash (FA) as a carrier material was developed and studied for its activity against the larval stages of major mosquito vector species.Methods:An indigenous isolate Bti (Vector Control Research Centre B17) was mass produced using a 100 l fermentor in soya-based medium. The bacterial biomass was mixed with lignite FA and made into WDP formulations. The most effective formulation was used for determining 50 per cent lethal concentration (LC50) against the larval stages of major mosquito vector species, effect on non-target organisms and mammalian systems using standard protocols.Results:Sixteen types of WDP formulations were prepared, of which the formulation containing bacterial biomass, FA and carboxymethyl cellulose was found to be the most effective. The LC50 values of the formulation against Culex quinquefasciatus, Aedes aegypti and Anopheles stephensi larvae were 0.0417, 0.0462 and 0.1091 mg/l, respectively. The formulation was found to be safe to non-target organisms found associated with the mosquito larval stages and also to mammalian systems.Interpretation & conclusions:The study shows that FA can be effectively used to replace commercially available carrier materials used in biopesticidal formulations.

Towards Bio-Encapsulation of Chitosan-Silver Nanocomplex? Impact on Malaria Mosquito Vectors, Human Breast Adenocarcinoma Cells (MCF-7) and Behavioral Traits of Non-target Fishes

In this study, we synthesized and bio-encapsulated a chitosan-silver nanocomplex (Ch-AgNPs), characterizing it by UV–Vis spectroscopy, FTIR, EDX, SEM, XRD and Zeta potential analyses. The bio-encapsulated chitosan-Ag nanocomplex (BNC) was efficient as scavenger of free radicals (DPPH and ABTS), if compared to Ch-AgNPs. In toxicity assays against breast cancer cells (MCF-7) the BNC triggered apoptotic pathways, leading to a decline of MCF-7 cell viability with IC50 of 17.79 μg/mL after 48 h of exposure. LC50 of BNC on Anopheles stephensi ranged from 54.65 (larva I), to 98.172 ppm (pupa) while Ch-AgNPs LC50 ranged from 4.432 (I) to 7.641 ppm (pupa). In the field, the application of Ch-AgNP (10 × LC50) lead to A. stephensi larval reduction to 86.2, 48.4 and 100% after 24, 48, and 72 h, while the BNC nanocomplex exhibited 68.8, 36.4 and 100% larval reduction, respectively. Both Ch-AgNPs and the BNC reduced longevity and fecundity of A. stephensi. As regards to non-target effects on fish behavioral traits, in standard conditions, Poecilia reticulata predation on A. stephensi larvae was 70.25 (II) and 46.75 larvae per day (III), while post-treatment with sub-lethal doses of BNC, predation was boosted to 88.5 (II) and 70.25 (III) larvae per day.

Effect of temperature and search area on the functional response of Anisops sardea (Hemiptera: Notonectidae) against Anopheles stephensi in laboratory bioassay

Present study was carried out to establish the influence of abiotic factors on foraging activities of a predatory hemipteran insect Anisops sardea against Anopheles stephensi larvae. The functional response of A. sardea was evaluated in variable density of prey items with variation in search area (100, 250, 500 and 1000ml water volume) and temperatures (20, 25 and 30°C). The results of laboratory bioassay revealed that prey consumption rate of predator species was positively related with increasing temperature and inversely related with increasing search area. Polynomial logistic regression equations and associated parameters showed that A. sardea exhibited a type II functional response in variable search area and type-III response at variable temperatures. Related response specific attack rates and handling times were also evaluated in presence of specific abiotic factors.