Biosurfactants produced by Bacillus subtilis A1 and Pseudomonas stutzeri NA3 reduce longevity and fecundity of Anopheles stephensi and show high toxicity against young instars

Anopheles stephensi acts as vector of Plasmodium parasites, which are responsible for malaria in tropical and subtropical areas worldwide. Currently, malaria management is a big challenge due to the presence of insecticide-resistant strains as well as to the development of Plasmodium species highly resistant to major antimalarial drugs. Therefore, the present study focused on biosurfactant produced by two bacteria Bacillus subtilis A1 and Pseudomonas stutzeri NA3, evaluating them for insecticidal applications against malaria mosquitoes. The produced biosurfactants were characterized using FT-IR spectroscopy and gas chromatography-mass spectrometry (GC-MS), which confirmed that biosurfactants had a lipopeptidic nature. Both biosurfactants were tested against larvae and pupae of A. stephensi. LC50 values were 3.58 (larva I), 4.92 (II), 5.73 (III), 7.10 (IV), and 7.99 (pupae) and 2.61 (I), 3.68 (II), 4.48 (III), 5.55 (IV), and 6.99 (pupa) for biosurfactants produced by B. subtilis A1 and P. stutzeri NA3, respectively. Treatments with bacterial surfactants led to various physiological changes including longer pupal duration, shorter adult oviposition period, and reduced longevity and fecundity. To the best of our knowledge, there are really limited reports on the mosquitocidal and physiological effects due to biosurfactant produced by bacterial strains. Overall, the toxic activity of these biosurfactant on all young instars of A. stephensi, as well as their major impact on adult longevity and fecundity, allows their further consideration for the development of insecticides in the fight against malaria mosquitoes

The distribution of Culex mosquitoes in Coimbatore, Tamil Nadu, India

Lymphatic filariasis is an infection with the filarial worms, <em>Wuchereria bancrofti</em>, <em>Brugia</em> <em>malayi</em> and <em>B. timori</em>. These parasites are transmitted to humans through the bite of an infected <em>Culex</em> mosquito and develop into adult worms in the lymphatic vessels, causing severe damage and swelling (lymphoedema). Mosquito control, in view of their medical as well as economical importance, assumes global importance. Geographic information system (GIS) is a powerful tool to analyse the distribution of mosquitoes and their relationship to different environmental factors, and can substantially improve our ability to quantify the impacts of demographic, climatic and ecological changes in vector distribution. In the present study <em>Culex</em> <em>quinquefasciatus</em>, <em>Culex</em> <em>tritaeniorhynchus</em> and <em>Culex</em> <em>gelidus</em> were recorded in the study area. Few other factors such as larval mosquito density, number of breeding sites, human population, etc. were also analysed for its impact on the distribution of <em>Culex</em> mosquitoes. Distribution of Culex in the present study affirmed that <em>C. quinquefasciatus</em> is predominant in the entire focal area, which explains the behavioural response and capability of the species in varied zones. Information gathered from this study is being used to construct a GIS-based mapping system for distribution of <em>Culex</em> mosquitoes in the Coimbatore District, Tamil Nadu, India

Rapid biosynthesis of silver nanoparticles using <i>Crotalaria verrucosa</i> leaves against the dengue vector <i>Aedes aegypti</i>: what happens around? An analysis of dragonfly predatory behaviour after exposure at ultra-low doses

<p><i>Aedes aegypti</i> is a primary vector of dengue, a mosquito-borne viral disease infecting 50–100 million people every year. Here, we biosynthesised mosquitocidal silver nanoparticles (AgNP) using the aqueous leaf extract of <i>Crotalaria verrucosa.</i> The green synthesis of AgNP was studied by UV–vis spectroscopy, SEM, EDX and FTIR. <i>C. verrucosa</i>-synthesised AgNPs were toxic against <i>A. aegypti</i> larvae and pupae. LC₅₀ of AgNP ranged from 3.496 ppm (I instar larvae) to 17.700 ppm (pupae). Furthermore, we evaluated the predatory efficiency of dragonfly nymphs, <i>Brachydiplax sobrina</i>, against II and III instar larvae of <i>A. aegypti</i> in an aquatic environment contaminated with ultra-low doses of AgNP. Under standard laboratory conditions, predation after 24 h was 87.5% (II) and 54.7% (III). In an AgNP-contaminated environment, predation was 91 and 75.5%, respectively. Overall, <i>C. verrucosa</i>-synthesised AgNP could be employed at ultra-low doses to reduce larval population of dengue vectors enhancing predation rates of dragonfly nymphs.</p