IMPACT OF SELECTED ESSENTIAL OILS AND PIPERONYL BUTOXIDE ON PYRETHROID RESISTANCE IN Anopheles gambiae IN OTA

Abstract

Malaria remains a major public health challenge in Nigeria, with rising pyrethroid resistance in Anopheles gambiae undermining vector control strategies. Resistance is largely driven by detoxification enzymes and target-site mutations. Although piperonyl butoxide (PBO) is widely used as an insecticide synergist, its environmental and health risks highlight the need for safer alternatives. This study evaluated the potential of basil and geranium essential oils to inhibit detoxification enzymes, enhance permethrin efficacy, and compared their effects to PBO in An. gambiae. Adult females were collected, morphologically identified, and allocated into treatment groups for WHO susceptibility bioassays, enzyme activity assays, and allele-specific PCR (AS-PCR) for kdr mutation detection. Mosquitoes were exposed to permethrin alone (0.75%), basil or geranium essential oils at 1 (10 μL/mL), 5 (50 μL/mL), and 10% (100 μL/mL) v/v, or sub-lethal synergist assays combining permethrin (0.75%) with basil (1%), geranium (1%), or PBO (4%). Permethrin alone produced 25% mortality, confirming resistance according to WHO criteria. As separate insecticides, basil oil induced 0, 90, and 100% mortality at 10, 50, and 100 μL/mL, respectively, while geranium oil induced 10, 100, and 100% mortality at the same concentrations. In synergist assays, basil + permethrin achieved 25% mortality, geranium + permethrin 55%, and PBO + permethrin 60%. Enzyme assays showed no significant variation in GST activity, whereas cytochrome P450 activity was significantly elevated in permethrin-only treatments (p < 0.05) but remained near-control levels with basil, geranium, and PBO. AS-PCR detected a high frequency of the kdr-west L1014F allele (R = 0.76), with most mosquitoes homozygous resistant (RR). These findings confirm strong pyrethroid resistance in An. gambiae from Ota and highlight geranium oil and basil oil, as promising environmentally friendly insecticides and synergists for malaria vector control.