The rice weevil (Sitophilus oryzae) is a pest of stored grain products such as rice, wheat, and corn. Essential oils represent a green environmentally-friendly alternative to synthetic pesticides for controlling stored-product insect pests. Launaea taraxacifolia is a leafy vegetable plant found in several parts of Nigeria. The leaves are eaten either fresh as a salad or cooked as a sauce. The essential oil obtained from fresh leaves of L. taraxacifolia was obtained by hydrodistillation and analyzed by gas chromatography/mass spectrometry (GC-MS). Twenty-nine compounds were identified, accounting for 100% of the oil composition. The major component classes were monoterpene hydrocarbons (78.1%), followed by oxygenated monoterpenoids (16.2%), sesquiterpene hydrocarbons (2.1%), oxygenated sesquiterpenoids (0.3%), and non-terpenoid derivatives (3.3%). The leaf essential oil was dominated by monoterpene hydrocarbons including limonene (48.8%), sabinene (18.8%), and (E)-β-ocimene (4.6%), along with the monoterpenoid aldehyde citronellal (11.0%). The contact insecticidal activity of L. taraxacifolia essential oil against Sitophilus oryzae was carried out; median lethal concentration (LC50) values of topical exposure of L. taraxacifolia essential oil were assessed over a 120-h period. The LC50 values ranged from 54.38 μL/mL (24 h) to 10.10 µL/mL (120 h). The insecticidal activity of the L. taraxacifolia essential oil can be attributed to major components limonene (48.8%), sabinene (18.8%), and citronellal (11.0%), as well as potential synergistic action of the essential oil components. This result showed L. taraxacifolia essential oil may be considered as a useful alternative to synthetic insecticides.
Mosquitoes are the most important single group of insect vectors of the causative parasites of several diseases including malaria, dengue and filariasis for which cheap, safe, locally available and environmentally benign control measures are being sought. This study aimed at determining the toxicity of smoke from pelletized leaf powder and essential oil of Hyptis suaveolens (L) against third instar larvae and 0-2 day old adult Anopheles gambiae respectively in the laboratory. Test larvae were exposed to various concentrations ranging from 0ppm (control) through 50 to 500ppm of leaf essential oil at ambient laboratory temperature (25±1 0 C) in standard bioassay for 96 hrs using Complete Randomized Block Design. Larval mortality was recorded at 24, 48, 72 and 96 hours of exposure. For exposure to pellets, 0-2 day old adult test insects were exposed to smoke from smoldering pellets having concentrations: 0% (Control), 20, 40, 60, 80 and 100% in glass fumigation chamber where the test smoke and insects were contained. Data from quantal responses were subjected to Probit analyses for determination of lethal concentration values. Results showed that essential oil and smoke from smoldering pellet were toxic to both larvae and adults at all concentrations respectively. The computed 24 hr-LC 50 of test essential oil against larvae is 1448 ppm; 48 hr-LC 50 551.47 ppm, 72 hrs LC 50 is 187.43 ppm and 96 hours LC 50 is 142.10 ppm, respectively. The insecticidal pellet LC 50 at 30, 60, 90 and 120 minutes values were 107.79%, 69.56%, 31.27% and 22.15%, respectively. The results show that H. suaveolens could be exploited as a plant based insecticide for the control of Anopheles mosquitoes and suggests the need for further work including field studies.
Aims: Aedes aegypti is a widely distributed mosquito and the primary vector of several arboviral diseases attracting major global health concerns. This laboratory study accessed the ovicidal and larvicidal activities of n-hexane extract of Murraya paniculata (L.) Jack leaves on eggs and first instar larvae of Aedes aegypti. Study Design: Conventional bioassay, Place and Duration of Study: Department of Zoology, ETF Laboratory and Central research laboratory, College of Medicine, University of Lagos, Idi-araba, between February and July 2021. Methodology: Eggs and larvae were exposed to various quantities of test plant extract ranging from 20ppm to 80ppm for 72 hours at ambient laboratory temperature(30\(\pm\)0.570c). Probit analyses and analysis of variance were used to analyze the data. Results: Results revealed that the plant extract recorded the highest ovicidal activity of 61% at 80 ppm concentration against the eggs of Aedes aegypti, after 72 hours. The LC50 values of ovicidal and larvicidal activities at 72hrs were 85.162ppm and 80.270ppm respectively, there was a significant difference between the ovicidal and larvicidal activity of each concentration while mortality increased with increasing concentration. Conclusion: The results suggest that n-hexane extract of M. paniculata can be used as an environmentally friendly method for the control of Aedes aegypti.
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