Studies on physiology, zoospore morphology and entomopathogenic potential of the aquatic oomycete: Lagenidium giganteum.

The oomycete Lagenidium giganteum, a facultative parasite of mosquito larvae requires exogenous sterols for the genesis of zoospores when grown saprobically. Growth media prepared from oil rich materials such as soy or sunflower seed were very effective inducers of virulent zoospores. The external morphology of zoospores of L. giganteum was studied with the aid of philips scanning electron microscope 515. Zoospores were ovoid, bluntly pointed with the groove parallel to the long axis and 0.7 x 1.4 microm. Insect cell walls are known to contain lipid and chitin. L. giganteum was tested for chitinase activity and found to possess 0.76 +/- SD0.14 chitinase activity. Use of oil seed for growth of the organism confirms phospholipase activity. Phospholipase production was studied further by egg-yolk plate method. Presence of these two key enzymes that can initiate host cell damage suggests the entomopathogenic potential of L. giganteum. L. giganteum failed to grow at 37 degrees C limiting its effectiveness in warmer climates. Introduction of this organism to variety of habitats with various mosquito species will demonstrate the efficacy of the organism as a bioinsecticide.