Effectiveness of control measures against mosquitoes at a constructed wetland in southern California

The effectiveness of larvicide and adulticide treatments against mosquitoes at a constructed wetland in San Jacinto, California was assessed with larv al surveys, trapping of emerging adults, and collections of host-seeking fe males by carbon dioxide-baited traps. Bacillus thuringiensis var, israelens is (Bti, Bactimos(R) pellets) applied at a rate of 19 kg/ha did not demonst rably affect Culex larval and emergent adult populations. Larval population s in the seven marshes of the wetland decreased from approximately one thir d-fourth instar larva/dip to undetectable levels following two applications of Bacillus sphaericus (Vectolex(R) CG) at a rate of either 19 or 23.6 kg/ ha. The largest decline in the number of adult mosquitoes emerging per day from vegetated regions of the wetland occurred after B, sphaericus treatmen ts. The Culex erythrothorax host-seeking population declined about 80-fold during September beginning three weeks after the first treatment with B. sp haericus; however, the Culex tarsalis host-seeking population did not decli ne abruptly until mid-October 1997. This result suggests that immigration o f females from other developmental sites might be an important factor influ encing the Cx. tarsalis host-seeking population at the wetlands. Safety con cerns required that insecticide applications were carried out during daylig ht hours, and two daytime applications of adulticide (Pyrenone(R)) in early August were ineffective against mosquitoes resting in the thick vegetation .