The asexual stages (presporangial mycelia) of Lagenidium giganteum cultured on sunflower seed extract were encapsulated in calcium alginate and remained infective to mosquito larvae, Culex quinquefasciatus, after storage at 15 degrees C for up to 75 days. Survival and zoospore release from the encapsulated mycelia persisted for up to 24 days after immersion in water. Encapsulated sexual stages (oospores), held at 23-26 degrees C for up to 35 days or frozen for 8-10 days, were infective to mosquito larvae for up to 48 days after immersion in water and during that time over 50% of the oospores germinated. In outdoor pools, encapsulated mycelia gave 100% control of Cx. quinquefasciatus at 6-7 days after treatment while encapsulated oospores gave 100% control at 11 days posttreatment.