Efficacy of botanical extracts from Callitris glaucophylla against Aedes aegypti and Culex annulirostris mosquitoes

Abstract

Using standard WHO methodology, this study investigated the susceptibility of 4(th) instar Aedes aegypti (L) and Culex annulirostris (Skuse) larvae to three extracts from Callitris glaucophylla (J. Thompson & L. Johnson) (1: steam distillation extract, 2: liquefied refrigerant gas extract, and 3: methanol reflux extract), lambda-cyhalothrin (a synthetic pyrethroid insecticide) and fenitrothion (an organophosphorous insecticide). Cx. annulirostris was significantly more susceptible than Ae. aegypti to all tested chemicals except lambda-cyhalothrin. Responses to the three C. glaucophylla extracts were exceptional for a botanical compound: Cx. annulirostris (LC(50) = 0.23, 9.53 and 38.95 mg/L) and Ae. aegypti (LC(50) = 0.69, 5.21 and 306.43 mg/L). Both Cx. annulirostris and Ae. aegypti larvae were significantly more susceptible to lambda-cyhalothrin (LC(50) = 0.00013 and 0.00016 mg/L) than fenitrothion (LC(50) = 0.0009 and 0.004 mg/L). As expected, the pyrethroid and organophosphorous insecticides were far more potent than the crude C. glaucophylla extracts. The steam distilled extract was fractionated and the major components guaiol and citronellic acid were identified and tested. Activities for these major components were lower than observed for the distillate. Minor components include lactones such as eldanolide, and future testing of minor components may indicate the active component.