Laboratory evaluation of Lagenidium giganteum (Oomycetes: Lagenidiales) in water from Contra Costa County, California, mosquito sources.

Six bioassays were performed to evaluate the efficacy of the fungus, Lagenidium giganteum, against mosquitoes in water collected from 75 sources. The fungus infected larvae of 4 genera and produced greater than 90% mortality in water from some of the creeks, artificial containers and the wild rice field tested during 4 of the assays. There was no larval mortality due to the fungus in water from irrigated pastures or marshes. Water quality parameters associated with L. giganteum infection varied among the bioassays; low measurements of total dissolved solids (TDS), hardness (CaCO3), conductivity, chemical oxygen demand (COD), ammonium nitrogen (NH3-N), phosphate (PO4) and salinity were significantly (P less than 0.05) correlated with fungal efficacy in one or more of the assays. Regression analyses selected TDS, CaCO3, COD, NH3-N and/or PO4 as the best predictors of larval mortality due to L. giganteum. Turbidity and pH were not correlated with fungal efficacy.