Lagenidium giganteumZoospores: Effects of Concentration, Movement, Light, and Temperature on Infection of Mosquito Larvae☆

Assays conducted with a California isolate ofLagenidium giganteumrevealed that the LC50against second-instarCulex quinquefasciatuslarvae in pond water was 26 zoospores/ml. The maximum distance that zoospores swam horizontally and infected second-instar larvae was 60 cm. The maximum depth from which zoospores moved upward in a column of water and infected larvae was between 30 and 40 cm. The release depth of zoospores in a column of water at which 50% larval mortality occurred was 19.6 cm. Free-swimming zoospores did not exhibit positive or negative attraction to incandescent light as evidenced by larval mortality. Survival of zoospores as indicated by mosquito larval mortality was greatest at 25°C and was similar at 30, 33, and 35°C. No infection occurred at 17°C and <20% larval mortality occurred at 19°C for any age of zoospores.