Effects of piperonyl butoxide on the toxicity of the organophosphate temephos and the role of esterases in the insecticide resistance of Aedes aegypti

Abstract

Introduction: The effects of piperonyl butoxide (PBO) on the toxicity of the organophosphate temephos (TE) and the role of esterases in the resistance of Aedes aegypti to this insecticide were evaluated. Methods: A. aegypti L4 larvae susceptible and resistant to TE were pre-treated with PBO solutions in acetone at concentrations of 0.125, 0.25, 0.5, 1, and 2% for 24h and subsequently exposed to a diagnostic concentration of 0.02mg/L aqueous TE solution. The esterase activity of the larvae extracts pre-treated with varying PBO concentrations and exposed to TE for three time periods was determined. Results: At concentrations of 0.25, 0.5, 1, and 2%, PBO showed a signifi cant synergistic effect with TE toxicity. High levels of esterase activity were associated with the survival of A. aegypti L4 larvae exposed to TE only. Conclusions: The results of the biochemical assays suggest that PBO has a signifi cant inhibitory effect on the total esterase activity in A. aegypti larvae.Keywords: Temephos. Insecticide resistance. Aedes aegypti. Esterases.Dengue fever, a major viral disease, is a serious public health problem, especially in tropical countries where the climate and urban culture provide optimal conditions for the development and proliferation of its main vector, the mosquito Aedes aegypti 1 . The control of A. aegypti is primarily based on the use of chemical and biological products that are integrated with environmental management programs. Public programs aimed at controlling mosquitoes are characterized by the use of commercial insecticides, including organophosphates and pyrethroids. The organophosphate temephos (TE) was widely used in Brazil to control A. aegypti larvae until recently; however, due to reports of vector resistance to this insecticide, this method was replaced by the National Dengue Control Program. Nevertheless, TE remains on the list of insecticides to control dengue in Brazil and may be used again in the future 2,3 .The resistance to insecticides has contributed to an increase in A. aegypti populations and the incidence of dengue cases in Asia, and Central and South America, especially in Brazil 2,4 .The biochemical mechanisms involved in the development of resistance to insecticides include detoxifi cation metabolism processes. Several enzymes and enzyme systems participate in these processes, including oxidases, esterases, and transferases 5 . These enzymes allow the insect to convert an insecticide to a nontoxic form or to rapidly eliminate the compound from the body.Synergists such as piperonyl butoxide (PBO) have been employed in an attempt to overcome resistance to insecticides. Synergists are known to act as an alternative substrate, competing with the insecticide and interfering with detoxification. Synergists also act allosterically to inhibit the binding sites of esterases and multifunction oxidases (MFOs), minimizing the amount of insecticide needed to control insects and the levels of environmental contamination by pesticide residues 6 .Several studies have demonstrate...

Monitoring resistance of Cydia pomonella (L.) Spanish field populations to new chemical insecticides and the mechanisms involved

“…This may be because the insects did not receive a sufficient amount of synergist to block their PSMO enzymatic system activity, and they were able to detoxify the insecticide. Increasing concentrations of PBO applied before the application of a diagnostic dose of temephos in the mosquito Aedes aegipty (L.) (Diptera: Culicidae) produced a significant mortality increase in a naturally resistant strain, but the lower concentration did not increase the mortality, and the same happened with Rhizopertha dominica (F.) (Coleoptera: Bostrychidae) and deltamethrin . Two major enzymatic systems are involved in the metabolism of pyrethroid insecticides: PSMO and EST .…”