Insect Resistance Mechanisms and How (not) to Start Statewide Surveillance

Understanding insecticide resistance mechanisms, their prevalence among mosquito species, and standard resistance testing methods are critical first steps in effectively managing resistance. These foundational concepts formed the basis of the first presentation during the Global Mosquito Resistance Management Virtual Summit, hosted by Valent BioSciences, held in late March of 2022.

“You might think, no, we don’t have resistant mosquitoes in my district. You do. The real question isn’t is resistance there or not, it’s how well are you selecting for it and curbing its development over time.”

Nicholas DeLisi, Entomologist/Lab Manager at St. Tammany Parish Mosquito Abatement (Slidell, LA), began his talk with a review of basic resistance dynamics: how insecticide applications select resistant individuals, whose heritable traits are then passed on to successive generations. He also provided an overview of resistance mechanisms and the random genetic mutations that give rise to resistance mosquito pheotypes.

Delisi went on to explain topical bioassay procedures (and results) conducted in the district’s lab on both susceptible and wild mosquito populations – showing evidence that wild populations in the area exhibit significant resistance.

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He demonstrated that on average, the lethal dose required for wild Culex quinquefasciatus populations in St. Tammany Parrish was 20x higher for naled (organophosphate) and 200x higher for resmethrin (pyrethroid) than in susceptible populations.

DeLisi concluded his presentation by recounting the challenges met by the Louisiana Mosquito Control Association in developing a statewide resistance program and database. Not only were efforts stalled by the global pandemic, but he also spelled out other challenges related to collecting, rearing and shipping live mosquitoes around the state.