Mass production potential of the bacto-helminthic biocontrol complex Heterorhabditis indica-Photorhabdus luminescens

Heterorhabditis indica is a potential agent for the biological control of grubs in sugarcane fields in India. The type strain LN2 was transferred to monoxenic cultures on its symbiont Photorhabdus luminescens and successfully produced on solid media. In liquid cultures, a mean dauer juvenile yield of 457 000 was obtained with a maximum of 648 000 per ml. Comparatively high yields have not been reported before. Therefore, costs related to the liquid culture production of H. indica will he lower than for other entomopathogenic nematodes currently used in biocontrol. Different bacterial clones had no significant influence on the dauer juvenile yields in liquid media. The exit from the dauer juvenile stage (recovery) after inoculation and the number of hermaphrodites significantly decreased when culture temperature was increased from 25-30 degreesC; the dauer juvenile yields were not affected. The cell density of P. luminescens in batch cultures was higher at 25 and 30 degreesC than at growth temperatures of 35 and 37 degreesC. In continuous culture the bacterial growth was inhibited when the growth temperature reached 38 degreesC. After approximately 60 h, the bacteria adapted to higher temperature and the growth rate increased again. When the temperature was further increased to 40 degreesC, the bacterial growth was inhibited.