Nutritional status significantly affects toxicological endpoints in the CDC bottle bioassay

Authors: Norris, Edmund; BLOOMQUIST, JEFFREY - University Of Florida

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/9/2021
Publication Date: 10/25/2021
Citation: Norris, E.J., Bloomquist, J.R. 2021. Nutritional status significantly affects toxicological endpoints in the CDC bottle bioassay. Pest Management Science. 78:743-748. https://doi.org/10.1002/ps.6687.
DOI: https://doi.org/10.1002/ps.6687

Interpretive Summary: The CDC Bottle Bioassay serves as an inexpensive and effective way to screen field-caught mosquitoes against a wide variety of insecticidal active ingredients and commercial formulations, with the goal of detecting resistant individuals. We wanted to assess the impact of nutritional status on the response of yellow fever mosquitoes in the CDC Bottle Bioassay. To do this, we ran the CDC Bottle Bioassay on mosquitoes that were fully fed with 10% sucrose water and those that were starved for 24 and 48 hr. Significant differences were observed in CDC Bottle Bioassay responses for mosquitoes that were starved compared to 10% sugar water fed mosquitoes. These differences were also observed in a pyrethroid-resistant stain of Aedes aegypti mosquitoes, indicating that nutritional status may significantly affect how resistance status is reported. We also exposed mosquitoes to permethrin in the CDC Bottle Bioassay that were 10% sugar water fed, water only fed, sugar only fed, and starved. This exploration demonstrated that water alone was enough to produce toxicological responses that were similar to 10% sugar water fed mosquitoes. Sugar only and starved mosquitoes were significantly more susceptible to insecticide exposure. Thus, mosquitoes should be hydrated before testing. Moreover, as significant differences were observed between starved and fed mosquitoes in a pyrethroid-resistant strain, some caution is appropriate when interpreting resistance/susceptibility diagnoses with this bioassay system.

Technical Abstract: The CDC Bottle Bioassay serves as an inexpensive and effective way to screen field-caught mosquitoes against a wide variety of insecticidal active ingredients and commercial formulations, with the goal of detecting resistant individuals. For this study, we were curious whether sucrose-water (10% w/v) feeding status had an impact on the response of Aedes aegypti mosquitoes to currently utilized insecticides. Starvation for 24 or 48 h decreased permethrin LT50 about 40%, with little difference in the two starvation times. There was less of an effect of starvation on malathion toxicity at the 24 h time point. Similar findings were also observed in a pyrethroid-resistant Puerto Rico strain challenged with permethrin, as mosquitoes starved for 48 h responded with higher mortality than the sugar-water fed group after 30 min exposure. This effect was also observed after starving Puerto Rico mosquitoes for 24 hr, but differences between starved and sugar-water fed mosquitoes were less pronounced. To test the impact of mosquito weight on toxicity, we measured weight under different 48 h nutritional conditions and found that sugar-water fed = sugar only fed > water-only fed = starved and that water fed mosquitoes were the most insecticide tolerant. The results indicate insect nutritional status is an important experimental variable, particularly hydration status of mosquitoes shortly before insecticide exposure. Thus, mosquitoes should be hydrated before testing. Moreover, as significant differences were observed between starved and fed mosquitoes in a pyrethroid-resistant strain, some caution is appropriate when interpreting resistance/susceptibility diagnoses with this bioassay system.