First report of Oscheius insectivorus (Körner, 1954) Andrássy, 1976 (Nematoda: Rhabditidae) from Iran with its efficacy against Chrysomela populi L. (Col.: Chrysomelidae) and Galleria mellonella L. (Lep.: Pyralidae).

Abstract

A population of Oscheius insectivorus was recovered from inside the body of a live scarab beetle collected from natural forests of Jafar Abad village, Golestan province, and was reported from Iran for the first time. The Iranian isolate of the species is characterized by 1103-1942 μm long females with their vulva at 46.9-57.4% of the body, tail 75-118 μm long, males with spicules 60.0-74.5 μm long, gubernaculum 23.7-32.2 μm long, and infective juveniles measuring 790-985 μm long. Females and males of the recovered population had shorter body when compared with the type population. Molecular identification of the recovered population was performed using the SSU and D2-D3 expansion segments of LSU rDNA, and corresponding phylogenetic trees were reconstructed and discussed. The pathogenicity of the Iranian isolate was evaluated on the larvae and adults of the poplar leaf beetle, Chrysomela populi, and the larvae of the wax moth, Galleria mellonella, under laboratory conditions. A suspension of 200 infective juveniles per ml (IJs/ml) of the nematode was most effective against third instar larvae of C. populi, causing 75% mortality 72 hours post-exposure. In adults, mortality reached 70% at the same concentration and exposure time. For G. mellonella larvae, O. insectivorus caused 50% mortality at 200 IJs/ml within 72 hours post-exposure. The lethal concentration 50 (LC50) values of the nematode were 77.71 and 94.06 IJs/ml for third instar larvae and adults of C. populi, respectively, and 217.04 IJs/ml for fifth instar larvae of G. mellonella 72 hours post-exposure at 25°C and 60% relative humidity.