Monitoring local mosquito populations for insecticide resistance is critical for effective vector-borne disease control. However, widely used phenotypic assays, which are designed to monitor the emergence and spread of insecticide resistance (technical resistance), do not translate well to the efficacy of vector control products to suppress mosquito numbers in the field (practical resistance). This is because standard testing conditions such as environmental conditions, exposure dose, and type of substrate differ dramatically from those experienced by mosquitoes under field conditions. In addition, field mosquitoes have considerably different physiological characteristics such as age and blood-feeding status. Beyond this, indirect impacts of insecticide resistance and/or exposure on mosquito longevity, pathogen development, host-seeking behavior, and blood-feeding success impact disease transmission. Given the limited number of active ingredients currently available and the observed discordance between resistance and disease transmission, we conclude that additional testing guidelines are needed to determine practical resistance—the efficacy of vector control tools under relevant local conditions— in order to obtain programmatic impact.

We compared the effectiveness of 4 different carbon dioxide (CO2) sources (sugar-fermented BG-CO2, sugar-fermented Fleischmann yeast, dry ice, and compressed gas cylinders) in attracting different mosquito species in 2 separate 4 × 4 Latin square trials. The CO2 generated by dry ice and the gas cylinders collected more Culex quinquefasciatus than the sugar-fermented BG-CO2 and Fleischmann yeasts during the 1st trial (16-h surveillance periods), but there was no significant difference in Aedes aegypti numbers. There were no significant differences between the different CO2 sources in collecting Cx. quinquefasciatus and Ae. aegypti mosquitoes in the 2nd trial (24-h surveillance periods). Catches for Culiseta inornata and Cx. tarsalis were too low in both experiments for formal statistical analysis. Data can be used to inform local mosquito surveillance programs, but the selection of a CO2 source will also depend on financial and logistical constraints.