Pest management in most sub-Saharan subsistence agriculture involves mainly the use of botanicals that are either applied as powders, solvent extracts, ash or essential oils. Two hydrogenated monoterpenes (α-pinene and 3-carene) from Cupressus sempervirens were tested against Sitophilus zeamais in the laboratory to evaluate the contact and fumigation effects on the mortality of adult and immature weevils, progeny production, and grain damage. Contact toxicity of the terpenes was investigated at these concentrations: 0.08, 4, 8 and 12 ppm (terpene/maize), while fumigant action was studied at the following doses: 1, 2, 3, and 4 ppm. The results indicate that insecticidal effects were concentration-dependent since mortality increased with dosage and exposure periods. After a 14-day exposure period at the concentration of 12 ppm of α-pinene and 3-carene/grain, more than 98% mortality of the mature weevils was observed at concentrations of 4.1333 and 1.642 ppm respectively and progeny production was reduced by 98% and 100%, respectively. When α-pinene and 3-carene were applied as fumigants, LC50s (lethal concentrations that generate 50% mortality) of 1.402 and 0.610 ppm were obtained after 24 h of exposure, respectively. At concentrations above 3 ppm, both monoterpenes acted as repellents to weevils and reduced grain damage by 80%. Both monoterpenes inhibited the development of immature stages of the weevil and reduced progeny by up to 94%. These compounds are very promising and effective and could be exploited as novel phytoinsecticides against the maize weevil.
The study was undertaken to evaluate the adulticidal efficacy of the methanolic leaf extracts and essential oils of Chenopodium ambrosioides, Hyptis suaveolens and Lippia adoensis against adults of Anopheles gambiae. A chemical profile of each plant extracts (qualitative phytochemical screening) and essential oil (GC/MS analysis) was also determined. Doses of 125, 250, 500 and 1000 mg/bottle of plant extracts and 25, 50, 100 and 200 mg/bottle of essential oils were prepared and tested using CDC bottles. In each plant extract, alkaloids, flavonoids, saponins, tannins, phenolic groups, terpenoids, fats and oils were presents. Major chemical constituents of essential oils were thymol (27.09%), sabinene (18.93%) and 4-carene (52.88%) in L. adoensis, H. suaveolens and C. ambrosioides, respectively. L. adoensis extract (at 1000 mg/bottle) and essential oil of H. suaveolens (at 200 mg/bottle) were the most potent causing 100% mortality of An. gambiae adults, 24 h post-exposure. Methanolic extract of L. adoensis (LC50= 20.20 mg/bottle) was the most effective compared to other extracts. Similarly, essential oil of H. suaveolens (LC50= 5.27 mg/bottle) was revealed as the most toxic on An. gambiae adults compared to other oils. Therefore, the extracts of L. adoensis and essential oil of H. suaveolens showed a high activity and should be recommended to be promoting as natural bioinsecticides to control mosquito adults.
The CH2Cl2-MeOH (30:70 v/v) extracts of the seeds of Mangifera indica (Mango), Persea americana (Avocado) and Dacryodes edulis (African plum) were evaluated for potential mosquito larvicidal activity against 3rd and 4th instar larvae of Aedes aegypti, Culex quinquefasciatus and Anopheles gambiae. Extracts were diluted with 1 mL of methanol and concentrations ranging from 1000 to 125 mg/L in 4 replicates each, were prepared in the volume of 100 mL in the plastic cups (250 mL). A volume of 1 mL of methanol added to 99 mL of tap water was prepared as negative control and Bi-one (1000 mg/L) constituted a positive control. In each test solution, 25 larvae of each mosquito species were separately transferred and larval mortality was recorded after 24 h post-treatment. As results, the three plant seed extracts applied at 1000 mg/L caused for at least 79% mortality of each mosquito species larvae assessed. The seed extract of P. americana (LC50 of 98.31, 129.24 and 136.26 mg/L, respectively against An. gambiae, Ae. aegypti and Cx. quiquefasciatus larvae) was the most potent followed by D. edulis (LC50 of 176.87 mg/L for An. gambiae, 198.68 mg/L for Ae. aegypti and 201.70 mg/L for Cx. quinquefasciatus) and M. indica (LC50 of 258.98 mg/L for An. gambiae, 297.35 mg/L for Ae. aegypti and 435.45 mg/L for Cx. quinquefasciatus). Globally, all the seed extracts were more toxic against An. gambiae larvae compared to other mosquito species and need further exploration for the development of a new botanical larvicide to reduce mosquito densities.
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