Laboratory evaluation of a Helicosporidium sp. (Protozoa: Helicosporida) as an agent for the microbial control of mosquitoes.

A Helicosporidium sp. isolated from diseased larvae of Culex pipiens L. in Egypt was assessed for its microbial control potential against mosquito larvae. Dose infectivity and dose mortality of the pathogen was determined for each larval instar of Cx. pipiens. Helicosporidium sp was infectious to Aedes caspius (Pallas), C. antennatus (Becker), C. perexiguus Theobald, and Culiseta longiareolata (Macquart). Using 24-hr exposures of first instar larvae to a range of concentrations between 50 and 5 x 10(3) spores/ml, Cx. antennatus and Cx. perexiguus were more susceptible than Cx. pipiens, Ae. caspius and Cs. longiareolata with LC50's of 5 x 10(2), 5 x 10(2), 1.6 x 10(3), 1.4 x 10(3), and 1.7 x 10(3), respectively. Current experiments shown that Helicosporidium spores were tolerant of freezing and storage at 5 degrees C, but not to desiccation. Production trails indicated that up to 6.2 x 10(8) spores could be routinely produced in individual cotton leaf worms, Spodoptera littolaris (Boisd) (Lepidoptera: Noctuidae).