Arsenic altered susceptibility to Bacillus sp. in Culex mosquitoes

Arsenic is a common aquatic pollutant worldwide, and yet limited information is available regarding the effects is has on aquatic insects. Previous studies have shown that relatively high concentrations of arsenic have a limited effect on aquatic insect survival. We wanted to test the hypothesis that though survival was not affected at these concentrations of arsenic, arsenic still causes physiological stress. We reared cohorts of larvae of Culex tarsalis and Culex quinquefasciatus (Diptera: Culicidae) in water containing 0 μg As/l, 1000 μg As/l of arsenate, or 1000 μg As/l of arsenate from first through fourth instars. Fourth instars were then exposed to the biological control agents Bacillus thuringiensis subsp. israelensis for 24 hours (Cx. tarsalis: 0, 0.005, 0.01, 0.02, 0.05, 0.08 ppm; Cx. quinquefasciatus: 0, 0.02, 0.05, 0.08, 0.10, 0.20 ppm) or Bacillus sphaericus for 48 hours (Cx. tarsalis: 0, 0.001, 0.002, 0.005, 0.01, 0.02 ppm; Cx. quinquefasciatus: 0, 0.005, 0.01, 0.02, 0.05, 0.08 ppm) and monitored for survival. Results from this study add to the growing body of literature on how arsenic affects insects, and how pollution could alter susceptibility to biological control agents.