The interspecific interactions between different larval instars of two aphidophagous predator species,M. corollaeand E. nigromaculatus were examined under laboratory conditions. Intraguild predation (IGP) between predators was studied in various larval densities of the predator and in the presence or absence of extraguild prey aphids after 24 hours. There was a highly significant difference of IGP at the different densities in the presence or absence of aphids between the 1^st instar larvae of M. corollae by the 2^nd instar larvae of E. nigromaculatus and when the 1^st instar larvae of M. corollae was confined with the 3^rd instar larvae of E. nigromaculatus. The highest IGP percentage by the 4^th instar larvae of E. nigromaculatus against the 1^st instar larvae of M. corollae was observed at the fifth level of density in the presence or absence of aphids. IGP on the 2^nd instar larvae of M. corollae by the 2^nd instar larvae of E. nigromaculatus differed significantly at the various densities in the absence of aphids, but no significant difference was found on IGP between them in the presence of aphids. The predation by the3^rd instarlarvae ofE. nigromaculatus against the 2^nd instar larvae of M. corollae rose at both fourth and fifth levels of density in the presence of aphids. Meanwhile, in the absence of aphids, the highest level of IGP was obtained at the fourth level of density. IGP rate by the 4^th instar larvae of E. nigromaculatus against the 2^nd instar larvae of M. corollae differed significantly at the different densities in the presence or absence of aphids. The influences of larval density and prey presence or absence on the incidence of intraguild predation among the two predator species were considered and the outcome of predatory interference between them is discussed.