Abstract
Due to ever-growing insecticide resistance in mosquito vectors and environmental contamination by synthetic insecticides, plants may be a source of alternative agents for mosquito control. Therefore, the aim of this study was to investigate the mosquito oviposition-deterrent and ovicidal activities of different solvent fractions and essential oils from Plectranthus glandulosus and Callistemon rigidus against three mosquito species, Aedes aegypti, Anopheles gambiae and Culex quinquefasciatus . For oviposition deterrence, 150 gravid females of each mosquito species were introduced in each cage. For ovicidal bioassay, 100 eggs and 1 raft of at least 100 eggs were exposed to 500 and 1000 ppm for fractions, 150 and 300 ppm for essential oils, 1000 ppm for WARRIOR®, and were assayed in the laboratory conditions. The same concentrations were used for oviposition deterrence. The oviposition deterrence was observed 72 h and the ovicidal activity 4 h post-treatment. P. glandulosus essential oil and hexane fraction utterly prevented gravid mosquitoes from laying eggs/rafts on oviposition traps as in WARRIOR®. There was relatively no mosquito eggs/rafts deposited in chloroform fraction of C. rigidus as observed in WARRIOR®. The hatching rates of P. glandulosus hexane fraction were reduced to 9.67, 15.33 and 28.33% against An. gambiae, Ae. aegypti and Cx. quinquefasciatus , respectively at 1000 ppm; 5 and 11.33%, respectively for the essential oil at 300 ppm with no egg hatched in An. gambiae treatments. Hexane fraction of C. rigidus recorded 14.33, 25.33 and 39.00% of hatching eggs against An. gambiae, Ae. aegypt i and Cx. quinquefasciatus , respectively at 1000 ppm. These results revealed that P. glandulosus and C. rigidus served as potent oviposition deterrents and ovicides against An. gambiae, Ae. aegypti and Cx. quinquefasciatus. Keywords : Plectranthus glandulosus, Callistemon rigidus , Mosquito, Oviposition, Ovicides.
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