Life Cycle of Nematode
A study was carried out of a Thai isolate of the entomopathogenic nematode, Heterorhabditis sp.. This isolate was collected from soil in Roi Et Province, Northeast Thailand. Studies of its biology emphasized its life cycle within the host insect ( Galleria mellonella), the effect of temperature on its growth and reproduction within the insect, and isolation of its symbiotic bacteria.
Results from studying its life cycle at room temperature (26Â±2 oC) revealed that the juveniles passed through four stages before becoming an adult (male or female). The adult female could be either hermaphroditic or amphimictic. The first generation of infective juveniles produced from the hermaphroditic female completed its cycle six days (144 hours) within the host insect. The amphimictic female then produced the second generation of infective juveniles, which could complete their life cycle in four days. After ten days, the infective juveniles gradually moved out of the dead body of the host insect.
Effect of Temperature
Low or high temperatures (15 oC or below, and 35 oC or above) caused the nematodes to stop growing and reproducing. The nematodes developed slowly at 20 oC, and produced only one generation of infective juveniles from hermaphroditic females in ten days. The optimum temperature for growth and reproduction was 25 - 30 oC.
A symbiotic bacterium was isolated from the haemolymph of G. mellonella infected with Heterorhabditis sp. for 48 hours. The bacterium colony was absorbed with bromthymol blue on NBTA medium. It was circular to irregular in shape, with a clear zone around the colony. It was greenish in color in the center, which was raised, opaque and undulated. The bacterium was classified as Photorhabdus sp. Heterorhabditis sp. It can be mass produced on a semi-solid media based on KDSM, SBSM or ESM formulae. The yield of infective juveniles was 349 million per liter of KDSM medium, 191 million per liter of SBSM medium, and 293 million juveniles per liter of ESM medium.
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