No abstract
Laboratory experiments were conducted to determine the salinity range over which North Carolina (NC) and Louisiana (LA) isolates of the fungus Lagenidium giganteum (Couch) grow vegetatively and infect mosquito larvae. The mycelial growth rates of the 2 isolates on nutrient agar were increased with 2.5 and 5.0 parts per thousand (ppt) of NaCI added and reduced with 7.5 ppt or more NaCI. The LA and NC isolates did not grow on agar containing 20 and 30 ppt NaCI, respectively. The concentrations of NaCI for 50% inhibition (ICso) of mycelial growth of the LA and NC isolates (10.9 and 12.0 ppt, respectively) were not significantly different (P > 0.05). The ability of the 2 isolates of L. giganteum to infect larvae of Aedes taeniorhynchus decreased as salinity of the water increased. The ICso values for the inhibition of infection in mosquito larvae by the LA and NC isolates (0.52 and 0.55 ppt NaCI, respectively) were not significantly different (P > 0.05). Microscopic examination of the fungus in saline and distilled water showed that NaCI inhibited the production of zoospores. In water containing 1.5 ppt NaCI there was complete inhibition of zoosporogenesis and mosquito infection in each isolate of L. giganteum. Zoosporogenesis was ca. 22 times more sensitive to salinity than was mycelial growth. ,
Laboratory experiments were conducted to determine the relative toxicity of certain insecticides, herbicides, and fungicides to the vegetative growth and zoospore production in North Carolina (NC) and Louisiana (LA) isolates of Lagenidium gigallleum. Zoospore production in both isolates was less tolerant than mycelial growth to most of the pesticides tested and, thus. the IC,,, values (inhibition concentration) for mycelial growth rate on agar underestimated toxicity. The most toxic pesticides to one or both isolates of L. giganteum were captan, gamma-SHC. DOT. toxaphene, chlorpyrifos, and fenthion. These pesticides produced at least 10% inhibition of mycelial growth rate or completely inhibited zoospore production at concentrations below 5 parts per million (ppm). The least toxic pesticides caused a 10% inhibition in mycelial growth rate and failed to inhibit zoospore production at concentrations greater that 50 ppm. These were ditlubenzuron, permethrin. temephos, and propoxur (LA isolate only). Pesticides of intermediate toxicity were: malathion, carbaryl. methoprene. alachlor, and atrazine. The two isolates differed substantially in their tolerance of the following pesticides: malathion, chlorpyrifos, toxaphene, carbaryl, propoxur, permethrin, and methoprene. At their recommended rates of application for control of mosquito larvae, methoprene, fenthion, malathion, and temephos would probably be compatible with both isolates of L. giganteum.
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