Characterisation of Steinernema carpocapsae populations from Serbia with notes on intraspecific variability and entomopathogenicity of their symbiotic and associated bacteria

Abstract

As part of a broader survey on entomopathogenic nematodes (EPN), two species, Steinernema carpocapsae and S. thesami , were found for the first time in Serbia at Mt Avala. Two populations of S. carpocapsae (AV10 and AV27) were characterised using morphological and molecular methods. Sequencing of the ITS rDNA region confirmed both isolates as S. carpocapsae . Morphometric examination of infective juveniles and first- and second-generation males revealed generally typical characteristics of S. carpocapsae , although notable intraspecific variation was observed. A comparison of morphometric characters among described S. carpocapsae populations available in the literature is provided. Bacteria associated with the nematode populations were isolated from infected Galleria mellonella larvae and identified by sequencing the 16S rRNA and rpoB genes as Xenorhabdus nematophila , Serratia marcescens , Stenotrophomonas maltophilia , Enterococcus casseliflavus , Bacillus cereus , B. paranthracis , and Priestia megaterium . Pathogenicity bioassays showed that oral administration of bacterial suspensions did not cause mortality in G. mellonella larvae, whereas direct injection into the haemocoel resulted in significant mortality for most isolates. The results expand knowledge of the morphological diversity of S. carpocapsae , pointing out some possible causes that may affect intraspecific variability and providing evidence that several members of the nematode-associated microbiota possess entomopathogenic potential when intrahemocoelically administered.