Topical application bioassay to quantify insecticide toxicity for mosquitoes and fruit flies

Authors: JENSEN, BROOK - Arizona State University; ALTHOFF, RACHEL - Arizona State University; RYDBERG, SARAH - Arizona State University; ROYSTER, EMMA - Arizona State University; Estep Iii, Alden; HUIJBEN, SYLVIE - Arizona State University

Submitted to: The Journal of Visualized Experiments (JoVE)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2021
Publication Date: 1/19/2022
Citation: Jensen, B., Althoff, R., Rydberg, S., Royster, E., Estep III, A.S., Huijben, S. 2022. Topical application bioassay to quantify insecticide toxicity for mosquitoes and fruit flies. The Journal of Visualized Experiments (JoVE). 179, e63391:1-23. https://doi.org/10.3791/63391.
DOI: https://doi.org/10.3791/63391

Interpretive Summary: We describe the methodology and importance of the topical application bioassay to measure insecticide susceptibility in mosquitoes and fruit flies. The presented assay is high-throughput, utilizes insect mass - thus allowing for calculating a mass-relativized lethal dose instead of concentration - and likely has lower variability than other similar methods.

Technical Abstract: The continued use of insecticides for public health and agriculture has led to widespread insecticide resistance and hampering of control methods. Insecticide resistance surveillance of mosquito populations is typically done through CDC bottle bioassays or WHO tube tests. However, these methods suffer from a high degree of variability in mortality data due to variable insecticide contact of the insect in such assays, the relatively small numbers of organisms tested, extensive variation in mass between strains, and issues with comparisons of the resulting data between strains. Here, we present the topical application assay, adapted as a high-throughput phenotypic bioassay for both mosquitoes and fruit flies, to test large numbers of insects at a range of insecticide concentrations. This assay 1) ensures consistent treatment and insecticide contact with every organism, 2) produces highly specific dose-response curves that account for differences in average mass between strains (which is particularly important for field collected organisms, and 3) allows for calculation of statistically rigorous median lethal doses (LD50) which are necessary for resistance ratio comparisons, thus being suitable for routine surveillance programs. This assay will be a complimentary tool for accurately phenotyping mosquito populations and, as illustrated using fruit flies, is easily adaptable for use with other insects. We content that this assay will help fill the gap between genotypic and phenotypic insecticide resistance in multiple insect species.