Palanisamy Mahesh Kumar

Larvicidal efficacy of Catharanthus roseus Linn. (Family: Apocynaceae) leaf extract and bacterial insecticide Bacillus thuringiensis against Anopheles stephensi Liston.

OBJECTIVE To explore the larvicidal activity of Catharanthus roseus (C. roseus) leaf extract and Bacillus thuringiensis (B. thuringiensis) against the malarial vector Anopheles stephensi (An. stephensi), when being used alone or together. METHODS The larvicidal activity was assayed at various concentrations under the laboratory and field conditions. The LC50 and LC90 values of the C. roseus leaf extract were determined by probit analysis. RESULTS The plant extract showed larvicidal effects after 24 h of exposure; however, the highest larval mortality was found in the petroleum ether extract of C. roseus against the first to fourth instars larvae with LC50=3.34, 4.48, 5.90 and 8.17 g/L, respectively; B. thuringiensis against the first to fourth instars larvae with LC50=1.72, 1.93, 2.17 and 2.42 g/L, respectively; and the combined treatment with LC50=2.18, 2.41, 2.76 and 3.22 g/L, respectively. No mortality was observed in the control. CONCLUSIONS The petroleum ether extract of C. roseus extract and B. thuringiensis have potential to be used as ideal eco-friendly agents for the control of An. stephensi in vector control programs. The combined treatment with this plant crude extract and bacterial toxin has better larvicidal efficacy against An. stephensi.

Do Nanomosquitocides Impact Predation of Mesocyclops edax Copepods Against Anopheles stephensi Larvae

Mosquitoes transmit serious human diseases, causing millions of deaths every year. The use of synthetic insecticides to control vector mosquitoes cause physiological resistance and adverse environmental effects, in addition to enormous operational costs. In this study, silver nanoparticles (AgNP) were biosynthesized using a cheap extract of the Acorus calamus rhizome, as reducing and stabilizing agent. The biosynthesized AgNP were characterized by using UV–Vis spectrophotometry, X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). R. calamus extract and green-synthesized AgNP showed ovicidal, larvicidal, pupicidal and adulticidal toxicity against the malaria vector Anopheles stephensi. In ovicidal experiments, egg hatchability was reduced by 100 % after treatment with 25 and 50 ppm of AgNP. In larvicidal and pupicidal assays, LC50 values of A. calamus extract were 219.06 ppm (I instar), 246.01 ppm (II), 285.79 ppm (III), 345.19 ppm (IV) and 470.93 ppm (pupa); green-synthesized AgNP were highly effective, with LC50 of 8.94 ppm (I), 11.64 ppm (II), 14.94 ppm (III), 19.15 ppm (IV) and 28.66 ppm (pupa). In adulticidal trials, A. calamus extract and AgNP showed LC50 of 251.71 ppm and 12.74 ppm, respectively. The predatory efficiency of the cyclopoid crustacean Mesocyclops edax in standard laboratory conditions was 71 % and 58 % against I and II instar larvae of A. stephensi, respectively. In an aquatic environment treated with ultra-low doses of AgNP, M. edax predation efficiency was 84 % and 69 %, respectively. Predation was higher against I instar larvae over other instars. Overall, these results suggest that A. calamus-synthesized AgNPs represents a concrete possibility for eco-friendly control of A. stephensi.