Isolation and molecular characterization of five entomopathogenic nematode species and their bacterial symbionts from eastern Australia

Abstract

Entomopathogenic nematodes (EPNs) are used in biological control of pest insects but their potential may be limited by strain availability from different bioregions and effectiveness against specific pests. Here, we isolated and characterized EPNs and their symbiotic bacteria from Australia where their diversity is scarcely known. We collected 198 soil samples from citrus orchards, grasslands and forests across temperate, subtropical and tropical eastern Australia. EPNs were isolated by baiting with mealworm, greater wax moth and Queensland fruit fly, The Australia’s most significant horticultural pest. We obtained 36 isolates which, according to DNA sequence analyses, represented five species, Heterorhabditis bacteriophora, Heterorhabditis indica, Heterorhabditis marelatus, Heterorhabditis zealandica and Steinernema feltiae, including the first report of H. marelatus from Australia, and H. indica and H. zealandica from New South Wales. Thirty-five isolates were baited with mealworm, one with fruit fly, and none with wax moth. Heterorhabditis marelatus was recovered from forests, H. bacteriophora from citrus orchards, S. feltiae from citrus orchards and grasslands, H. indica and H. zealandica from all three habitats. According to bacterial DNA analyses, Photorhabdus heterorhabditis occurred in H. zealandica and a reference strain of H. bacteriophora, Photorhabdus laumondii in H. bacteriophora and H. marelatus, Photorhabdus tasmaniensis in H. indica and H. bacteriophora, and Photorhabdus namnaonensis in H. zealandica. Unexpectedly, Pseudomonas protegens and Delftia acidovorans were found in S. feltiae while its expected symbiont Xenorhabdus remained undetected, possibly due to our approach. The newly isolated EPNs should be tested as biological control agents against pest insects.