The present study deals with the green synthesis of silver nanoparticle from the aqueous leaf extracts of Leucas aspera and Hyptis suaveolens as reducing agent and to investigate the larvicidal activity of synthesized silver nanoparticles. The synthesized silver nanoparticles were characterized by Ultraviolet and visible absorption spectroscopy (UV), Fourier transform-infrared spectroscopy (FT-IR), X-ray spectroscopy (XRD), Field emission scanning electron microscope (FESEM) and High-resonance transmission electron microscopy (HRTEM) analysis. The nanoparticles are spherical, hexagonal, triangular and polyhedral in shape and the size of the Silver nanoparticles (AgNPs) of L. aspera was found to be in the range of 7–22 nm and AgNPs of H. suaveolens was 5–25 nm. Larvicidal bioassay with synthesized AgNPs synthesized from L. aspera and H. suaveolens extract, showed 100% mortality at 10 mg/L against Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus with LC50 of 4.02, 4.69, 5.06 mg/L and LC90 of 11.22, 12.09, 12.74 mg/L and LC50 of 4.63, 4.04, 3.52 mg/L and LC90 of 12.07, 10.99, 09.61 respectively. These results suggest that the synthesized AgNPs of L. aspera and H. suaveolens have the potential to be used as an ideal eco-friendly agent for the control of the mosquito larvae.

Vector control is facing a threat due to the emergence of resistance to synthetic insecticides. Insecticides of plant origin my serve as an alternative biocontrol technique in the future. The aim of the present study was to evaluate the larvicidal activity of fractions and compounds from the whole-plant methanol extracts of Leucas aspera on the fourth-instar larvae of Aedes aegypti, Anopheles stephensi, and Culex quinquefasciatus. The larvae were exposed to fractions with concentrations ranging from 1.25, 2.25, 5, 10, and 20 ppm and isolated compounds. After 24 h exposure, larval mortality was assessed. Among the eight fractions, four from hexane extractions showed potent larvicidal activity against tested mosquito species at 20 ppm concentration. The isolated compound catechin showed pronounced larvicidal activity at very low concentrations. The LC50 and LC90 values of catechin were 3.05 and 8.25 ppm against Ae. aegypti, 3.44 and 8.89 ppm against An. stephensi, and 3.76 and 9.79 ppm against C. quinquefasciatus, respectively. The isolated compound was subjected to spectral analyses (GC-MS, FTIR, (1)H NMR, and (13)C NMR) to elucidate the structure and to compare with spectral data literature.

Essential oil obtained by hydrodistillation of the leaves of Acalypha fruticosa Forssk (Euphorbiaceae) was analysed by GC and GC-MS methods. Forty components were identified in the oil which totally constituted 97.4 %. The oil is characterized by the abundance of caryophellanes with β-caryophyllene (42.0 %), α-humulene (11.1 %), isocaryophyllene (4.3 %) and caryophyllene oxide (5.2 %). Trans-phytol (15.2 %) is the second major component of the oil. This is the first report of the isolation and characterization of the essential oil from an Acalypha genus.