Screening of bacteria isolated from Galleria mellonella (Lepidoptera: Pyralidae) larvae infected with novel entomopathogenic nematodes


Abstract: Major bacterial species developing in Galleria mellonella larvae infected with different entomopathogenic nematodes (EPN) were isolated by plating serial dilutions of insect haemolymph. On average 1, and at most 2 different bacterial isolates, were collected from each insect-EPN association. Nematodes involved in the research were collected from soil in different areas of Italy and Algeria, and were previously identified as Steinernema and Heterorhabditis species.Bacterial cultures were screened against insects of different orders, including Lepidoptera (Malacosoma neustria and Lymantria dispar) and Diptera (Musca domestica and Ceratitis capitata). In total 80 bacterial isolates were assayed by incorporating either the cell fractions or the culture supernatants in comparative experiments involving reference strains of Bacillus thuringiensis, Photorhabdus luminescens and of Xenorhabdus nematophila. The majority of bacterial isolates were toxic to lepidopteran larvae, while around 20 of them showed significant toxicity against fly larvae and/or adults. Bacteria showing the highest mortality levels (> 50%) on flies were submitted to identification through 16S rRNA gene sequencing, which highlighted the effectiveness of species belonging to different genera including Serratia, Pseudomonas, Alcaligenes, and Stenotrophomonas.

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