Adulticidal Activities and Synergistic Effects of Citrus Aurantiifolia Peels and Hyptis spicigera Leaves Essential Oils against Anopheles gambiae s.l. (Diptera: Culicidae)

Abstract

Research on new plant-based insecticides meets the need for an alternative to address mosquito resistance to synthetic insecticides. This study assessed the adulticidal activity and synergistic effects of essential oils (EOs) from Citrus aurantiifolia peels and Hyptis spicigera leaves on female adults of Anopheles gambiae s.l. The extraction yields were on the order of 0.17 and 0.11%, respectively, for C. aurantiifolia and H. Spicigera EOs obtained by hydrodistillation. The phytochemical composition of the EOs was analysed by Gas Chromatography coupled with Mass Spectrometry (GC-MS). GC-MS revealed that the essential oils of C. aurantiifolia and H. spicigera contained high amounts of monoterpene compounds (100% and 77.45%, respectively). Adulticidal activity was assessed using WHO and CDC bottle bioassays at concentrations of 2.5, 5, 7.5 and 10 mg/ml/btl. The EOs of both plants caused significant concentration-dependent Knock down and adulticidal activities. Individually, H. spicigera EOs had more adulticidal effects (LC50 = 4.42 mg/ml/btl) than did C. aurantiifolia EOs (LC50 = 6.79 mg/ml/btl). An EO mixture 25%Ca + 75%Hs from C. aurantiifolia and H. spicigera had synergistic effects (CI = 142.84; SF = 1.42) on female Anopheles gambiae adults. Combinations of the two plant EOs considerably optimize their insecticidal effectiveness.