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BACKGROUND: In the perpetual struggle to manage mosquito populations, there has been increasing demand for the development of biopesticides to supplant/complement current products. The insecticidal potential of Xenorhabdus and Photorhabdus has long been recognized and is of interest for the control of important mosquitoes like Aedes albopictus which vectors over 20 different arboviruses of global public health concern. RESULTS: The larvicidal effects of cell‐free supernatants, cell growth cultures and cell mass of an extensive list of Xenorhabdus and Photorhabdus spp. was investigated. They were quite effective against Ae. albopictus causing larval mortality ranging between 52–100%. Three Photorhabdus spp. and 13 Xenorhabdus spp. release larvicidal compounds in cell‐free supernatants. Cell growth culture of all tested species exhibited larvicidal activity, except for Xenorhabdus sp. TS4. Twenty‐one Xenorhabdus and Photorhabdus bacterial cells (pellet) exhibited oral toxicity (59–91%) against exposed larvae. The effect of bacterial supernatants on the mosquito eggs were also assessed. Bacterial supernatants inhibited the hatching of mosquito eggs; when unhatched eggs were transferred to clean water, they all hatched. Using the easyPACId approach, the larvicidal compounds in bacterial supernatant were identified as fabclavine from X. szentirmaii and xencoumacin from X. nematophila (causing 98 and 70% mortality, respectively, after 48 h). Xenorhabdus cabanillasii and X. hominickii fabclavines were as effective as commercial Bacillus thuringiensis subsp. israelensis and spinosad products within 5 days post‐application (dpa). CONCLUSION: Fabclavine and xenocoumacin can be developed into novel biolarvicides, can be used as a model to synthesize other compounds or/and can be combined with other commercial biolarvicides. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Photorhabdus spp. are the only known terrestrial bioluminescent bacteria. We show that the bioluminescence produced by these bacteria reduces scavenging activity on the insect cadavers they colonize. Photorhabdus spp. are the symbiont of the insect pathogenic nematodes Heterorhabditis spp. Together they kill insects and colonize the cadaver. The function of their bioluminescence has been the subject of debate, but here for the first time we demonstrate an ecological benefit. In our experiments, fewer Photorhabdus temperata -infected cadavers than uninfected cadavers were scavenged, but only in dark conditions where their bioluminescence would be visible. This was the case both in the field and in laboratory experiments with Lehmannia valentiana slugs (the primary scavengers found in our field tests). We also show that L. valentiana is innately deterred from scavenging on uninfected cadavers in proximity to light imitating the bioluminescence of Photorhabdus, indicating that luminescence can be a deterrent independent of chemical cues. We propose a multimodal defence where bioluminescence works together with the chemical defences also produced by Photorhabdus to deter scavengers, such as slugs, from feeding on the host cadaver, with the potential for aposematism. [ABSTRACT FROM AUTHOR]

Entomopathogenic nematodes (EPNs) belonging to the families heterorhabditidae (genus Heterorhabditis) and steinernematidae (genus Steinernema) are mutualistically associated with bacteria in the family Enterobacteriaceae (Photorhabdus spp. for Heterorhabditis and Xenorhabdus spp. for Steinernema). At present, there are 100 Steinernema and 17 Heterorhabditis species and 20 Xenorhabdus and 4 Photorhabdus species. In general, each EPN species has its own bacterial species, but a given bacterial species may be associated with more than one EPN species. The EPNs' natural habitat is the soil where the nematode-bacterium complex infects many different insect species killing them within 48 h. EPNs have been isolated from many different islands and from all continents except antarctica. Because EPNs and their associated bacteria are safe to humans, other vertebrates, and plants, can effectively kill soil insect pests in a short time, serve as an alternative to chemical pesticides, are easily massed produced in vivo and in vitro, and do not require registration in many countries, a number of EPN species have been produced commercially to target soil and plant-boring pests in high value crops. Moreover, the associated bacteria produce antibiotics and other compounds that have potential to be used against human, veterinary, and plant pathogens. [ABSTRACT FROM AUTHOR]