Abstract
The mechanisms of action of the complex including entomopathogenic nematodes of the genera Steinernema and Heterorhabditis and their mutualistic partners, i.e., bacteria Xenorhabdus and Photorhabdus, have been well explained, and the nematodes have been commercialized as biological control agents against many soil insect pests. However, little is known regarding the nature of the relationships between these bacteria and the gut microbiota of infected insects. In the present study, 900 bacterial isolates that were obtained from the midgut samples of Melolontha melolontha larvae were screened for their antagonistic activity against the selected species of the genera Xenorhabdus and Photorhabdus. Twelve strains exhibited significant antibacterial activity in the applied tests. They were identified based on 16S rRNA and rpoB, rpoD, or recA gene sequences as Pseudomonas chlororaphis, Citrobacter murliniae, Acinetobacter calcoaceticus, Chryseobacterium lathyri, Chryseobacterium sp., Serratia liquefaciens, and Serratia sp. The culture filtrate of the isolate P. chlororaphis MMC3 L3 04 exerted the strongest inhibitory effect on the tested bacteria. The results of the preliminary study that are presented here, which focused on interactions between the insect gut microbiota and mutualistic bacteria of entomopathogenic nematodes, show that bacteria inhabiting the gut of insects might play a key role in insect resistance to entomopathogenic nematode pressure.
Highlights
Coleoptera is the largest order of insects, representing over 400,000 of known species
As bacteria proliferate in the insect’s body, their antibiotic activity steadily grows to reach a maximum between days 3 and 5 of infection, i.e., when the host is already dead [32,33]
There has only been a unidirectional relationship imposed by entomopathogenic bacteria (EPB) through the production of a number of substances that inhibit the growth of insect gut bacteria
Summary
Coleoptera is the largest order of insects, representing over 400,000 of known species. Scarab larvae exploit a variety of niches, which range from rotting organic matter and dead tree trunks to freshly growing roots. Using these resources, they have become pests in agriculture and forestry. Of the approximately 150 scarab species that were recorded in Central Europe, damage is predominantly caused by only four native species: Melolontha melolontha, Melolontha hippocastani, Amphimallon solstitialis, and Phyllopertha horticola [2] These pests are difficult to control due to the cryptic position of larvae in the soil and the usually nocturnal activity of adults [3]
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