Parasitism of newly-hatched Aedes sierrensis (Diptera: Culicidae) larvae by Lambornella clarki (Ciliophora: Tetrahymenidae) following habitat flooding.

Host-parasite interactions between Lambornella clarki (Ciliophora: Tetrahymenidae) and its natural host, Aedes sierrensis (Diptera: Culicidae), were studied in newly flooded treeholes in northern California between 1986 and 1989. First instar host larvae hatched within 1 to 4 hr of flooding, while free-living trophonts of L. clarki appeared between 7 and 24 hr. As early as 24 hr after flooding, ciliates initiated the first parasite cycle by forming cuticular cysts on first instar larvae; by 64 hr, cysts were observed on larvae collected from all positive holes during all years. While larvae with as many as 12 cysts were observed, most supported only 1 cyst, and successful infections were established by the entry of a single ciliate into the host's hemocoel. Among treehole populations, the proportion of larvae with L. clarki cysts ranged from 2 to 100% at 48 hr indicating that enzootics and epizootics develop rapidly in newly flooded treeholes. Average attack rates from all holes by year ranged between 17.0 and 44.4%. Ciliates began entering hosts 48 to 72 hr after flooding, but some larvae escaped parasitization by molting to the second instar before ciliates penetrated the cuticle. In some treeholes, opportunistic microorganisms entered larvae with the invading ciliates and killed both the host and parasite.