Date of Award:

12-2025

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

Scott A. Bernhardt

Committee

Scott A. Bernhardt

Committee

Ricardo Ramirez

Committee

Kim Hageman

Committee

Carol von Dohlen

Committee

Kelsey Graham

Abstract

Chemical insecticides are commonly used to manage the damage to crops caused by agricultural pest insects. Reliance on insecticides for pest management has resulted in insecticide resistance in many insect species worldwide. Alfalfa weevils (Hypera postica) and lygus bugs (species within the genus, Lygus), are major pests to alfalfa hay and seed respectively and cause significant economic damage. The goal of this dissertation was screen Utah alfalfa fields for resistant alfalfa weevil and lygus bug populations, investigate genetic mutations that can influence resistance in alfalfa weevils, and establish which species of lygus bugs are present in Utah alfalfa fields. First, I investigated the concentrations of a commonly used insecticide, lambda-cyhalothrin, needed to kill susceptible alfalfa weevils and lygus bugs. Using this information, I determined diagnostic concentrations and exposure times for susceptible weevils and lygus bugs using a technique commonly used in mosquito insecticide resistance research. The diagnostic concentrations and exposure times are used to determine if a population is resistant to an insecticide, and I used these to screen multiple field populations for resistance. I then screened for genetic mutations in alfalfa weevils that are often found in other resistant insect species. Finally, I identified what species of lygus bugs are present in different alfalfa fields to begin to investigate whether species abundance influences resistance levels in a field. This research is useful because it identifies resistant populations of alfalfa weevils and lygus bugs in Utah, establish baseline metrics that can be used to screen more populations for resistance. It also opens the door for future researchers to further explore resistant mutations in alfalfa weevils, as well and continue to investigate how variations in lygus bug species abundance influences resistance.

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