Intraguild predation among different larval instars of metasyrphus corollae (f.) (diptera: syrphidae) and exochomus nigromaculatus (goeze) (coleoptera: coccinellidae)

The interspecific interactions between different larval instars of two aphidophagous predator species, M. corollae and 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 1st instar larvae of M. corollae by the 2nd instar larvae of E. nigromaculatus and when the 1st instar larvae of M. corollae was confined with the 3rd instar larvae of E. nigromaculatus. The highest IGP percentage by the 4th instar larvae of E. nigromaculatus against the 1st instar larvae of M. corollae was observed at the fifth level of density in the presence or absence of aphids. IGP on the 2nd instar larvae of M. corollae by the 2nd 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 the 3rd instar larvae of E. nigromaculatus against the 2nd 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 4th instar larvae of E. nigromaculatus against the 2nd 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.