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Larvicide Resistance: Investigating and Adapting to an Emerging Threat Symposium

Larvicide Resistance: Investigating and Adapting to an Emerging Threat Symposium

41 - Lack of cross resistance between S-methoprene and L. sphaericus in Culex pipiens from the Chicago, IL region

Tuesday, March 4, 2025

2:57 PM – 3:09 PM AST

Location: 208 B

Abstract: High levels of S-methoprene resistance were detected in Culex pipiens populations throughout the Chicago, IL region in 2023. Unfortunately, resistance to one active ingredient rarely means the population is only resistant to that chemical, cross resistance is often also at play. Previous literature suggests that resistance to S-methoprene can induce resistance to other active ingredients, notably Lysinibacillus sphaericus. We investigated the presence of cross resistance in 35 populations of Culex pipiens in three mosquito control districts: North Shore MAD, Northwest MAD, and Des Plaines Valley MAD. Significant S-methoprene was once again detected in almost all populations sampled. However, cross resistance to L. sphaericus was not detected in the districts where L. sphaericus has never been used. Resistance to L. sphaericus was only detected in populations from NSMAD, where L. sphaericus based products have been used historically. We hypothesize that because our 'Culex pipiens' mosquitoes are hybrids of Cx. pipiens, Cx. pipiens molestus, and Cx. quinquefasciatus, and JH sensitivity is so critical to the mosquito life cycle, these populations have evolved different ways of resisting the effects of S-methoprene that do not cause a cross resistance to L. sphaericus. The exact mechanisms behind S-methoprene resistance are yet to be investigated or characterized.

Presenter(s)

Kristina Lopez, PhD

Research Entomologist
North Shore Mosquito Abatement District, Illinois, United States

Co-Author(s)

PI

Patrick Irwin, PhD (he/him/his)

Entomologist & Assistant Director
Northwest Mosquito Abatement District, Illinois, United States
MT

Mark Tomek

Biologist
Des Plaines Valley Mosquito Abatement District, Illinois, United States
RH

Robert Holub

Director
Des Plaines Valley Mosquito Abatement District, Illinois, United States
SP

Susan Paskewitz, Ph.D.

Professor
University of Wisconsin - Madison, Wisconsin, United States
LB

Lyric Bartholomay, Ph.D.

Professor
University of Wisconsin - Madison, Wisconsin, United States
Mark Clifton, PhD

Executive Director
North Shore Mosquito Abatement District, Illinois, United States