Previous studies have used C and N isotope ratios to investigate the use of different food resources such as plant and animal detritus by container-breeding mosquitoes. This study is the first to report on the potential food resources assimilated by larval mosquitoes in agricultural and reference wetlands. Larval mosquitoes (Diptera: Culcidae) were sampled, along with their potential food resources, from agricultural and reference wetland habitats throughout a seasonal hydroperiod. IsoSource mixing model results indicated that food resources had greater δ¹⁵N isotope values in agricultural wetlands compared with cypress-gum swamps. In February, Aedes vexans (Meigen) and Culex territans Walker larvae fed primarily on lower quality food resources (coarse particulate organic matter and sediment) based on C:N. In contrast, higher quality food resources (fine particulate organic matter) were utilized by Anopheles spp. throughout the study and by Psorophora columbiae (Dyer and Knab) in May. This research contributes to a more comprehensive understanding of the food resources available and assimilated by larval mosquitoes in agricultural wetlands.