BIOEFFICACY OF TWO BOTANICAL OILS AGAINST ANOPHELES MOSQUITOES [DIPTERA: CULICIDAE]

Abstract

Senna hirsuta and Annona muricata are common plant species with diverse medicinal uses. This study investigated the bioefficacy of two botanical oils against developmental stages of Anopheles mosquitoes, repellent potentials as well as In vivo studies on determinations of skin irritant potentials using albino rats (Rattus norvegicus). Treatments were administered at different concentrations (0.5g/ml, 1.0g/ml, 1.5g/ml, 2.0g/ml, 2.5g and 3.0g/ml). Oils from the plants were extracted and tested against the developmental stages of Anopheles mosquitoes at 60mins intervals for four hours. The active ingredients in the essential oils were profiled using Gas Chromatography-Mass Spectrometer (GC-MS). This experiment was laid out in completely randomized design with three replicates. Data obtained were subjected to analysis of variance (ANOVA) and means were separated using New Duncan’s multiple range test (DMRT) at 5% level of significance. Larvicidal result obtained showed that 6.67% mortality was recorded by A. muricata oil at 0.5g/ml for 60mins. However at maximum concentration (3.0g/ml), S. hirsuta, A. muricata and their combination recorded maximum mortality of 58.33%, 78.33% and 98.33% respectively. Also, minimum concentration of 0.5g/ml for both plant oils tested against Anopheles mosquito pupae recorded 5% mortality at 60mins, however no mortality was recorded when the oils were tested individually. Maximum pupae mortality for S. hirsuta (35%) and A. muricata (41.33%) were recorded at 3.0g/ml maximum concentration. Furthermore, the adult at maximum time of exposure (240mins) and maximum treatment (3.0g/ml), S. hirsuta and A. muricata recorded maximum mortality of 28.33% and 38.33% respectively while their combination produced a significantly higher mortality of 48.33%. Result obtained at all levels and life stages showed a concentration and time of exposure dependent activity against An. mosquitoes since the percentage mortality was observed to increase with increase in concentration and time of exposure. Lethal concentration of 50 (LC50) for the larvae at 240mins showed that the effect of the oil combination on larvae (1.19g/ml) was more than the pupae (4.24g/ml) and the adult (5.29g/ml). Similarly, lethal concentration of 90 (LC90), for the larvae at 240mins also showed that the effect of the oil combination on larvae (5.88g/ml) was more than the pupae (37.43g/ml) and the adult (52.53g/ml). Senna hirsuta and Annona muricata exhibited repellent potentials against An. mosquitoes with no sign of skin irritation (erythema and oedema) after 72hrs. The bioefficacy of the oil extracts was traceable to the presence of two major classes of compounds: fatty acids and terpenoids. However the quantity of oleic acid (46%), and other classes of compounds like ketones and linoleic acid identified in A. muricata suggest its better efficacy. In conclusion, these findings suggest that S. hirsuta and A. muricata oil extracts have potential natural insecticidal properties hence can be integrated into vector management for both indoor and outdoor mosquito control.