Due to the global health problems associated with mosquito-borne diseases, over two million people primarily in the tropical countries are at risk. The widely and commonly used chemical method though effective, has some major disadvantages making insect control practically difficult. In view of the above, it is unavoidable to search for new molecules, which are eco-friendly, cheaper, and safer. The present study deals with evaluation of bioactive potential of two commonly occurring plants against mosquitoes presenting an alternative to the conventional chemical methods. Essential oils extracted by steam distillation from rhizome of Zingiber officinalis and leaf and stem of Achyranthes aspera were evaluated for larvicidal, attractant/repellent, and oviposition attractant/deterrent activity against two mosquito species viz. Aedes aegypti and Culex quinquefasciatus. The highest larvicidal activity, i.e., LC(50) = 154 ppm and LC(50) = 197 ppm for A. aegypti and C. quinquefasciatus, respectively was shown by Z. officinalis. This oil also offers 5-h protection at the concentration of 0.5 mg/cm² from both mosquito species. The highest oviposition deterrence activity was exhibited by A. aspera stem oil, i.e., 100% and 85.71%, in case of A. aegypti and C. quinquefasciatus, respectively, at the concentration of 0.1%. These results reveal that both these oils have control potential against A. aegypti and C. quinquefasciatus.
The management of house fly, Musca domestica has become immensely important to prevent epidemics of many detrimental diseases. In view of this objective, the present study demonstrates the efficacy of lemongrass (LG) and tea tree essential oils (TTEOs) against M. domestica . The TTEO proved to be more lethal against larvae and adults of M. domestica depicting an LC 50 at 14.88 mg/ dm 3 which was 17.19 mg/ dm 3 for LGEO. In contrast, pupicidal effect of LGEO was much higher (LD 50 , 14.49 µl/0.25L) as compared to TTEO. The LGEO drastically reduced the total body sugar, glycogen and protein contents by 3.29, 2.95 and 7.56 fold, respectively, contrasting with high influence of TTEO on lipid content of the late 3rd instar larvae. A considerable reduction in gut enzymes secretion was observed due to treatment of EOs thereby altering gut physiology of the insect. Moreover, significant inhibition of acetylcholine esterase (AchE) was also observed with LGEO at LC 50 concentration (5.33 mg/ml) inhibiting insect neurotransmission. The gas chromatography-mass spectrometric (GC-MS) analysis of the LGEO showed 12 major compounds dominated by Citral whereas TTEO contained only 5 major compounds. Further analysis by field emission scanning electron microscopy (FESEM) revealed distortion and shrinkage of larval bodies caused by the treatment of EOs. These overall observations brand LG and TT-EOs as potential organic-insecticides against M. domestica . Graphic Abstract Supplementary Information The online version of this article (10.1007/s40011-020-01220-z) contains supplementary material, which is available to authorized users.
The Rauvolfia tetraphylla leaf extract with different solvents n-hexane, chloroform, acetone and methanolwere tested for larvicidal, ovicidal, oviposition attractant/deterrent activities. Their effect on larval nutritionalreserve against Culex quinquefasciatus was also studied. Larval mortality was observed after 24 hoursexposure. The LC50 values for n-hexane, chloroform, acetone, methanol extracts are 16.80, 91.56, 214.85,44.68 ppm, respectively. The mean percentage hatchability of the ovicidal activity was observed 48 hourspost treatment. For R. tetraphylla, methanolic extract exhibited 56 % egg hatchability at 125 ppm. The effectiveoviposition repellency was 100 % at 320 ppm and the oviposition activity index value -1 was shown by nhexaneextract of R. tetraphylla. The fourth instar of C. quinquefasciatuswhere exposed to LC50 concentrationof extracts and its on larval nutritional reserves was checked. All extracts showed moderate effect on larvalnutritional reserves, i.e. changes in total concentration of sugar, glycogen, lipid and protein. The averagevalues of total sugar, glycogen, lipid and protein are 9.47, 32.32, 54.50, 183.35 μg/larvae was found infourth instar larvae of C. quinquefasciatus. From the all-leaf extracts, the methanol extract affects the totalsugar, lipid; n-hexane extract to glycogen and acetone extract to protein of fourth instar larvae of the mosquitoand decreases up to 3.39, 20.71, 11.18, 91.05 μg/larvae, respectively. These results reveal that the R. tetraphyllaleaf extracts have the control potential against C. quinquefasciatus.
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