RESUMEN
The efficacy of Steinernema siamkayai is a new species that isolate in Thailand and the well known previous species are Steinernema carpocapsae and Steinernema riobrave against 3rd instar larvae of common cutworm, Spodoptera litura, and last instar larvae of greater wax moth, Galleria mellonella was evaluated under laboratory condition. The optimal temperature for new entomopathogenic nematode, S. siamkayai at 50 and 100 IJs per larvae to penetrate into S. litura and G. mellonella larvae were highly suitable during 25 to 30 degrees C. The toxicity value in term of LC50 of S. siamkayai to S. litura larvae at age of 10 and 12 days were indicated that 37.75 (r2 = 0.92) and 61.16 (r2 = 0.95) IJs per larva after 72 hours of post infection, respectively. Moreover, S. siamkayai was better adapted to high temperatures and caused higher mortality at 35 degrees C than S. carpocapsae. According to the results of this research, the investigation should be further conducted in order to develop increasing efficacy of S. siamkayai and symbiotic bacteria. In addition, especially, the specificity of S. siamkayai to the insects should also be investigates.