Toxicological implications of the developmental environment in two Aedes sp. vector mosquitoes
Bilbo, Thomas R.
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Mosquitoes are one of the most important insects worldwide because of their role in transmitting pathogens that cause human and animal diseases. Their public health importance has led to extensive global efforts to control both the larvae and adults and these efforts often implement the use of chemical and biological insecticides. The efficacy of these insecticides in controlling larval mosquitoes can be modified by a number of factors in the aquatic environment such as pH, temperature, resource conditions, competition, predation, and other chemicals. Understanding and predicting how each of these stressors modifies insecticide toxicity is important so that mosquito control tactics can be optimized. The goal of this research was to determine how mosquito control insecticides interact with two stressors in the developmental environment: a biotic stressor, larval crowding, and a chemical stressor, exposure to the neonicotinoid thiamethoxam. Results show that larval crowding during insecticide exposure can significantly influence toxicity to the pyrethroid insecticide, permethrin, and that this effect can occur with seemingly innocuous changes in larval density. Possible mechanisms for this effect were investigated. Induced detoxification enzymes do not appear to be a factor, but density-modified larval exposure is likely a mechanism. Results for thiamethoxam exposure showed that at higher sub-lethal concentrations, thiamethoxam interacts with Bti and temephos synergistically, but at certain lower sub-lethal concentrations thiamethoxam pre-exposure increases larval tolerance to both larvicides. When tested alone, thiamethoxam exposure significantly alters sex ratio by disproportionately killing female larvae, likely due to slower female development rate. This research provides important insights into how mosquitoes may respond to control efforts when various environmental stressors are present. Understanding the influence larval crowding and neonicotinoids have on mosquitoes and their control is vital in predicting disease transmission and ensuring the efficacy and longevity of mosquito control programs.