Aedes aegypti are mosquitoes responsible for spreading viruses such as Dengue, Zika, and Chikungunya. Ae. aegypti is usually controlled with pesticides like organophosphates, which main mechanism of action is the acetylcholinesterase (AChE) inhibition. AChE is in charge of the hydrolysis of acetylcholine, also AChE has been identified as a possible resistance mechanism in mosquitoes. In this research, the resistance to the organophosphate insecticides Malathion, Chlorpyrifos, and Temephos of both wild (Piedecuesta strain) and standard (Rockefeller strain) larvae of Aedes aegypti was determined by WHO methodology. The total proteins and cholinesterase (ChE) rates were quantified for both strains using Bradford and Ellman methods, respectively. The residual cholinergic activity and type of inhibition were determined in larvae pre-exposed to sublethal concentration of the insecticides. The results of the research showed that the wild-type strain was susceptible to Temephos (RR50 3.8) and highly resistant to Malathion (RR50 13.8) and Chlorpyrifos (RR50 15.2). Quantification of the total protein in the larvae exposed to water revealed a 24.3% protein overproduction in Piedecuesta strain than in Rockefeller strain that can be related to metabolic changes or genetic modifications, and it is possibly involved in resistance. Larvae of Piedecuesta strain exposed to Malathion expressed 53.4% less in protein level than those exposed to DMSO 1% (control), and those exposed to Chlorpyrifos had 52.8% less than the control. In the case of Rockefeller strain exposed to Chlorpyrifos, the total protein expression was 62.1% less than the control. It was found that in Piedecuesta strain Malathion inhibited 82.5% of ChE, while Chlorpyrifos inhibited them by 25.3%. In the case of Rockefeller strain, Chlorpyrifos inhibited 81.9% of ChE. It was concluded that Malathion and Chlorpyrifos could act as allosteric cholinergic inhibitors. In Piedecuesta strain, Malathion may operate as an anticompetitive inhibitor, while Chlorpyrifos as a mixed inhibitor. In Rockefeller strain, Chlorpyrifos could work as an anticompetitive inhibitor. The different inhibition ratios and types of ChE inhibition, in larvae of both strains post-exposure to chlorpyrifos, indicated that Piedecuesta strain possibly has an insensitive AChE or the gene that codifies AChE has a genetic mutation. Results suggested that in this case the resistance of Aedes aegypti wild strain is probably related to AChE modifications.

Possible link between resistance of an Aedes aegypti chlorpyrifos resistant wild strain and changes in the protein expression and acetylcholinesterase inhibition

ACS Fall 2021

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