Date of Award


Degree Name

Master of Science



First Advisor

Lydy, Michael


Pyrethroid-resistant Hyalella azteca with genetically-confirmed voltage gated sodium channel mutations were identified at three geographically isolated locations in Central California. In December 2013, H. azteca were collected from Mosher Slough in Stockton, CA, a site with reported pyrethroid concentrations at approximately twice the LC50 for laboratory-cultured H. azteca and shipped to Southern Illinois University Carbondale. These H. azteca have been maintained in pyrethroid-free culture since December, 2013 with one supplement of organisms from the same site in March, 2014. Abundant research exists on fitness costs of insecticide resistance to pest species including reduced fecundity, fertility, reduced overwintering success, and reduced survival to adulthood. The current study showed that after 22 months in culture, resistant animals had approximately 53 times higher tolerance to permethrin than non-resistant H. azteca. After 16 months in culture, the resistant animals maintained complete loss of the wild-type allele at the L925 locus and had non-synonymous substitutions that resulted in either a leucine-isoleucine or leucine-valine substitution. Finally, the resistant animals showed lower reproduction, lower upper thermal tolerance, and were more sensitive to the common contaminants DDT, copper (II) sulfate, and NaCl. As shredders that consume epiphytes, animal and plant detritus, and filamentous algae, H. azteca aid in nutrient cycling through the breakdown and fragmentation of detritus and can serve as an important food source for larger invertebrates, fish, amphibians, and waterfowl. The results of the current study also hold implications for biomonitoring programs, toxicity testing, and laboratory culture procedures, as cryptic species complexes with varied sensitivities could dramatically alter results of these programs.




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