Antibacterial activity of hot aqueous and methanolic extracts prepared from six plants (Terminallia chebula, Terminallia bellerica, Phyllanthus emblica, Punica granatum, Lawsonia alba and Mikania micrantha) used in traditional folk medicines of India were screened against five pathogenic bacteria (Staphylococcus aureus MTCC 2940, Bacillus subtilis MTCC 441, Escherichia coli MTCC 739, Proteus vulgaris MTCC 426 and Enterobacter aerogenes MTCC 111). The highest antibacterial potentiality was exhibited by the methanolic leaf extract of T. chebula, followed by the aqueous fruit extract of T. bellerica. The leaf extract of T. chebula can be considered to be as equally potent as the most effective antibiotics, such as ciprofloxacin, gentamycin, kanamycin, ofloxacin and cephalexin. A sensitivity test performed with commonly used sensitivity test disks resulted in the appearance of multiple drug resistance phenotypes of the bacteria tested. A comparison of data in the inhibition zones of pathogenic bacteria showed that gentamycin, ofloxacin, kanamycin and tobramycin were effective against all of the bacterial strains tested.

Background: Vector control is facing a threat due to the emergence of resistance to synthetic insecticides. Insecticides of botanical origin may serve as suitable alternative biocontrol techniques in the future. Although several plants have been reported for mosquitocidal activity, only a few botanicals have moved from the laboratory to field use, because they are poorly characterized, in most cases active principals are not determined and most of the works are restricted to preliminary screening. Solanum villosum is a common weed distributed in many parts of India with medicinal properties, but the larvicidal activity of this plant has not been reported so far.

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The present study was carried out to establish the larvicidal activities of crude and solvent extracts of Solanum nigrum L. leaves against Culex quinquefasciatus Say as target species. The results indicated that the mortality rates at 0.5% concentration were highest amongst all concentrations of the crude extracts tested against all the larval instars at 24, 48 and 72 h of exposure. Result of log probit analysis (at 95% confidence level) revealed that lethal concentration LC(50) and LC(90) values gradually decreased with the exposure periods in bioassay experiment with the crude plant extract. The results of regression analysis of crude extract of S. nigrum revealed that the mortality rate is positively correlated with the concentration of the extracts. Mature leaves of S. nigrum were also extracted with six different solvents [viz. petroleum ether, benzene, ethyl acetate, chloroform: methanol (1:1 v/v), acetone and absolute alcohol] to determine the best extractant for subsequent isolation and characterization of active ingredient. Mortality rate with ethyl acetate extract was significantly higher (p < 0.05) than other extracts when 50-ppm doses were used. The corresponding LC(50) value of acetone, absolute alcohol, petroleum ether, chloroform: methanol (1:1 v/v), benzene and ethyl acetate extracts were 72.91 ppm, 59.81 ppm, 54.11 ppm, 32.69 ppm, 27.95 ppm and 17.04 ppm, respectively, after 24 h of exposure period. Results of this study show that the ethyl acetate extract of S. nigrum may be considered as a potent source of a mosquito larvicidal agent.

Crude mature leaves extract of Day Jasmine, Cestrum diurnum (Solanaceae: Solanales), was investigated for larvicidal activities against Culex quinquefasciatus, the vector of human filariasis. All the graded concentrations (0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, and 3% v/v) showed significant (P < 0.05) larval mortality, and results of regression equations revealed that the mortality rates were positively correlated with the concentrations of the extract (R (2) close to 1). LC(50), LC(95), and LC(99) values were calculated at different time intervals, and the lowest value was recorded at the 72-h bioassay for third-instar larvae. Significant changes in the larval mortality (F < 0.05) was also recorded between the periods of exposure and between instars during t test and single analysis of variance analysis. No mortality was noticed for nontarget organisms, such as Oreochromis niloticus niloticus and Chironomid larvae within 72 h of postexposure to 1%, 2%, and 3% crude plant extract under the laboratory condition. Qualitative and chromatographic analysis of the crude extract of C. diurnum revealed the presence of many bioactive phytochemicals. The bioassay experiment with the third-instar larval form established that the presence of a steroid compound (R (f), 0.67) was responsible for mosquitocidal activity.

The methanol leaf extracts of Glochidion neilgherrense, Cinnamomum wightii and Leucas linifolia are highly toxic even at low doses proven to be useful for larvicidal, pupicidal and adulticidal activity against Culex quinquefasciatus. The extraction of Glochidion neilgherrense, Cinnamomum wightii and Leucas linifolia are dose dependent and the mortality of the larvae increases as the doses of the sample were increased. Among all the instars, the fourth instar larvae were less susceptible to the plant extracts than first instar larvae. The mortality caused by some neural and muscular disturbance by the presence of variety of active compounds such as cytotoxic diterperiods, lactones and flavonoids in the plants. It was observed that the increase in concentration of extracts increased the potential activity of biocides against Culex quinquefasciatus. The decrease in egg hatchability was found to be dose dependent. There was increase in the larval-pupal duration, developmental duration, decrease in fecundity and egg hatchability, biting deterrency, in our study. The extract showed ovipositional deterrence and effective repellence against Culex quinquefasciatus at different concentration, with the observation on that maximal egg were laid in lower concentration of the extract and control. In oviposition deterrent and gravid mortality assay, the OAI values also indicated that the gravid and oviposited females were repelled by extracts and the reduced oviposition was due to the greater mortality of adults before they oviposited, caused by treatment of plant extract which contained of variety of active compounds. All the concentration of plant extracts hared promising mosquito repellency properties when tested against the adult mosquitoes of Culex quinquefasciatus. In the biting deterrency results, increasing in the concentration of plant extracts from 1% to 4% was found to increase the biting deterrency percentage.

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