Behavioral Response of Aedes aegypti Mosquito towards Essential Oils Using Olfactometer.

BACKGROUND: Aedes aegypti mosquito is responsible for transmitting human diseases like dengue and chikungunya. Personal or space protection with insect repellents is a practical approach to reducing human mosquito contact, thereby minimizing disease transmission. Essential oils are natural volatile substances from plants used as protective measure against blood-sucking mosquitoes. METHODS: Twenty-three essential oils were evaluated for their repellent effect against Ae. aegypti female mosquito in laboratory conditions using Y-tube olfactometer. RESULTS: The essential oils exhibited varying degree of repellency. Litsea oil showed 50.31%, 60.2 %, and 77.26% effective mean repellency at 1 ppm, 10 ppm and 100 ppm respectively, while DEET exhibited 59.63%, 68.63%, 85.48% and DEPA showed 57.97%, 65.43%, and 80.62% repellency at respective above concentrations. Statistical analysis revealed that among the tested essential oils, litsea oil had effective repellency in comparison with DEET and DEPA against Ae. aegypti mosquito at all concentration. Essential oils, DEET and DEPA showed significant repellence against Ae. aegypti (P< 0.05) at all 3 concentration tested. CONCLUSION: Litsea oil exhibited effective percentage repellency similar to DEET and DEPA. The essential oils are natural plant products that may be useful for developing safer and newer herbal based effective mosquito repellents.

Isolation and characterization of Vagococcus sp from midgut of Culex quinquefasciatus (Say) mosquito.

BACKGROUND & OBJECTIVES: Mosquito gut is a rich source of microorganisms. These microorganisms exhibit close association and contribute various physiological processes taking place in mosquito gut. The present study is aimed to characterize two bacterial isolates M19 and GB11 recovered from the gut of Culex quinquefasciatus mosquito collected from Bhuj and Jamnagar districts of Gujarat, India. METHODS: Both the strains were characterized using polyphasic approach including, phenotypic characterization, whole cell protein profiling and sequencing of 16S rRNA gene and groESL region. RESULTS: Sequences of 16S rRNA gene of M19 and GB11 were 99% similar to Vagococcus carniphilus and Vagococcus fluvialis. But phenotypic profile, whole cell protein profile and sequence of groESL region of both isolates were found to be similar to V. fluvialis. CONCLUSION: Based on phenotypic, genotypic and protein profiling, both the strains were identified as V. fluvialis. So far this species was known from domestic animals and human sources only. This is the first report of V. fluvialis inhabiting midgut of Cx. quinquefasciatus mosquito collected from Arabian sea coastal of India.

Aggregation responses of Cimex hemipterus F. to semiochemicals identified from their excreta.

BACKGROUND & OBJECTIVES: Bedbug Cimex hemipterus lives in cracks and crevices, and shows aggregation activity in the harbourage containing its fecal matter. Limited information is available on the chemicals influencing this aggregation behaviour in C. hemipterus. Possible components responsible for aggregation, if identified and evaluated can be helpful in designing bedbug management. METHODS: Study on the isolation and identification of chemicals from the excreta extract responsible for aggregation has been carried by GC-MS. The compounds identified were evaluated at different concentrations to C. hemipterus and their attraction index was determined. RESULTS: The GC-MS analysis of the excreta extract resulted in identification of 33 different types of semiochemicals such as esters, carboxylic acids, alcohols, aldehydes, ketones and other hydrocarbons. Among these 33 compounds of various groups, the carboxylic acid (E)-2-hexenoic acid and the aldehyde (E)-2-hexenal found to elicit highest positive aggregation behavioural response in all the stages followed by hexenal. INTERPRETATION & CONCLUSION: The fecal matter influence the aggregation behaviour in C. hemipterus. (E)-2-hexenoic acid, hexanoic acid, (E)-2-hexenal and hexanal found to exhibit aggregation in various stages of bedbug life cycle. These chemical components can be further exploited for designing and development tool for management of bedbugs.

Differential Larval Toxicity and Oviposition Altering Activity of Some Indigenous Plant Extracts against Dengue and Chikungunya Vector Aedes albopictus.

BACKGROUND: Mosquitoes are well known as vectors of several disease causing pathogens. The extensive use of synthetic insecticides in the mosquito control strategies resulted to the development of pesticide resistance and fostered environmental deterioration. Hence in recent years plants become alternative source of mosquito control agents. The present study assessed the larvicidal and oviposition altering activity of six different plants species-Alstonia scholaris, Callistemon viminalis, Hyptis suaveolens, Malvastrum coromandelianum, Prosopis juliflora, Vernonia cinerea against Aedes albopictus mosquito in laboratory. METHODS: Leaf extracts of all the six plants species in five different solvents of various polarities were used in the range of 20-400ppm for larval bioassay and 50,100 and 200ppm for cage bioassay (for the study of oviposition behavior) against Ae. albopictus. The larval mortality data were recorded after 24 h and subjected to Probit analysis to determine the lethal concentrations (LC50), while OAI (Oviposition activity index) was calculated for oviposition altering activity of the plant extracts. RESULTS: Vernonia cinerea extract in acetone and C. viminalis extract in isopropanol were highly effective against Aedes albopictus larvae with LC50 value 64.57, 71.34ppm respectively. Acetone extract of P. juliflora found to be strong oviposition-deterrent which inhibited >2 fold egg laying (OAI-0.466) at 100ppm. CONCLUSION: Vernonia cinerea and C. viminallis leaf extracts have the potential to be used as larvicide and P. juliflora as an oviposition-deterrent for the control of Ae. albopictus mosquito.

Midgut microbial community of Culex quinquefasciatus mosquito populations from India.

The mosquito Culex quinquefasciatus is a ubiquitous species that serves as a major vector for west nile virus and lymphatic filariasis. Ingestion of bloodmeal by females triggers a series of physiological processes in the midgut and also exposes them to infection by these pathogens. The bacteria normally harbored in the midgut are known to influence physiology and can also alter the response to various pathogens. The midgut bacteria in female Cx. quinquefasciatus mosquitoes collected over a large geographical area from India was studied. Examination of 16S ribosomal DNA amplicons from culturable microflora revealed the presence of 83 bacterial species belonging to 31 bacterial genera. All of these species belong to three phyla i.e. Proteobacteria, Firmicutes and Actinobacteria. Phylum Proteobacteria was the most dominant phylum (37 species), followed by Firmicutes (33 species) and Actinobacteria (13 species). Phylum Proteobacteria, was dominated by members of γ-proteobacteria class. The genus Staphylococcus was the largest genus represented by 11 species whereas Enterobacter was the most prevalent genus and recovered from all the field stations except Leh. Highest bacterial prevalence was observed from Bhuj (22 species) followed by Nagrota (18 species), Masimpur (18 species) and Hathigarh (16 species). Whereas, least species were observed from Leh (8 species). It has been observed that individual mosquito harbor extremely diverse gut bacteria and have very small overlap bacterial taxa in their gut. This variation in midgut microbiota may be one of the factors responsible for variation in disease transmission rates or vector competence within mosquito population. The present data strongly encourage further investigations to verify the potential role of the detected bacteria in mosquito for the transmission of lymphatic filariasis and west nile virus. To the best of our knowledge this is the first study on midgut microbiota of wild Cx. quinquefasciatus from over a large geographical area.

Transcriptome analysis of Anopheles stephensi embryo using expressed sequence tags.

Germ band retraction (GBR) stage is one of the important stages during insect development. It is associated with an extensive epithelial morphogenesis and may also be pivotal in generation of morphological diversity in insects. Despite its importance, only a handful of studies report the transcriptome repertoire of this stage in insects. Here, we report generation, annotation and analysis of ESTs from the embryonic stage (16-22 h post fertilization) of laboratoryreared Anopheles stephensi mosquitoes. A total of 1002 contigs were obtained upon clustering of 1140 high-quality ESTs, which demonstrates an astonishingly low transcript redundancy (12.1 percent). Putative functions were assigned only to 213 contigs (21 percent), comprising mainly of transcripts encoding protein synthesis machinery. Approximately 78 percent of the transcripts remain uncharacterized, illustrating a lack of sequence information about the genes expressed in the embryonic stages of mosquitoes. This study highlights several novel transcripts, which apart from insect development, may significantly contribute to the essential biological complexity underlying insect viability in adverse environments. Nonetheless, the generated sequence information from this work provides a comprehensive resource for genome annotation, microarray development, phylogenetic analysis and other molecular biology applications in entomology.