In order to evaluate the potensial of Heterorhabditis sp. incontrolling B. longissima bioassays was conducted in IndonesianResearch Institute for Spices and Medicinal Crops, Bogor from November2010 until March 2011. Infective juveniles (IJ) of the nematodes wereharvested by putting dead Tenebrio molitor on a filter paper placed in apetri dish containing 30 ml of water. IJs in the larval body will then go outand live in the water. The suspension was then diluted 1,000 times andthen population counted under a binocular microscope and repeated 3times. IJ population is obtained by dissolving 10 ml suspension to obtain7,000; 3,500; 1,750; 875; 438; and 0 IJs/ml of water. Each treatment wastested on 10 larvae, pupae, and adults by spraying 2 ml IJ suspension.Mortality observations were made at 24, 48, and 72 hours after infestation(HAI). The results showed that the highest Heterorhabditis sp.pathogenicity was found in larvae stadium followed by pupae and adultstadia. In the 3,500 IJ population/ml of water, larvae, imago, and pupaemortalities in 24 HAI were approximately 73, 63, and 10%, respectivelyand were not significantly different with 7,000 IJ/ml of water. LC 50 valuesof Heterorhabditis sp. on the larvae, adult, and pupae in 72 HAI were1,492; 2,622; and 800,818 IJ/ml of water, respectively.