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Graphical abstract Highlights • Xenorhabdus and Photorhabdus supernatants were effective on mobile stages of Tetranychus urticae. • The bacterial supernatants exhibited weak ovicidal activity. • Efficacy of Xenorhabdus szentirmaii and X. nematophila supernatants was higher than other bacterial species. • X. szentirmaii, X. nematophila supernatants and their combination significantly decreased T. urticae in pots. Abstract The effects of secondary metabolites produced by the following symbiotic bacteria, Xenorhabdus szentirmaii , X. nematophila , X. bovienii , X. cabanillasii , Photorhabdus luminescens and P. temperata, associated with entomopathogenic nematodes, were investigated against various developmental stages of Tetranychus urticae (Acari: Tetranychidae) using cell-free bacterial supernatants in Petri dishes. In addition, the effects of the most active bacterial supernatant(s) found in Petri dish experiments were tested on T. urticae in pot experiments. All studies were conducted at 25 ± 1 °C temperature, 70 ± 5% relative humidity and a light cycle of 16 h in a climate room. The result of the Petri dish experiments showed that the supernatants had little or no effect on the egg stage, as less than 4% mortality was recorded. Depending on the bacterial supernatant, mortality in the other stages was 46–97% for larvae, 30–96% for protonymphs, 41–92% for deutonymphs, 92–100% for adult males and 46–93% for adult females. Control mortalities ranged from 1−7% for larvae, 2–9% for protonymphs, 4–10% for deutonymphs, 6–10% for adult males and 4–8% for adult females. Among supernatants tested, X. szentirmaii and X. nematophila were the most efficacious with mortality greater than 90% on the mobile stages of T. urticae. According to the results from pot experiments, the supernatants of X. szentirmaii and X. nematophila , singularly and in combination, significantly reduced the T. urticae population. However, the mixture of X. szentirmaii and X. nematophila supernatants did not increase efficiency to reduce T. urticae population compared to each supernatant alone. Further studies are warranted to find the active compound(s) in the supernatants of X. szentirmaii or and X. nematophila and assess whether the supernatant(s) has the potential of being a practical and economical control agent for T. urticae. [ABSTRACT FROM AUTHOR]

[Display omitted] • Photorhabdus bacteria are bioluminescent terrestrial bacteria. • Cadavers with certain Photorhabdus spp. are bioluminescent and pigmented. • Some Photorhabdus infected cadavers are not consumed by scavengers. • Red coloration/bioluminescence from Photorhabdus do not deter on ants & crickets. Photorhabdus spp. and Xenorhabdus spp. bacteria produce a variety of molecules that inhibit bacterial and fungal contamination as well as deter scavenging invertebrates and some vertebrates in soil. Certain Heterorhabditis / Photorhabdus- infected insect cadavers can be bioluminescent in the dark and/or turn red from the production of anthraquinone pigments. The role of these traits remains unresolved. The aim of the present study was to evaluate the role of red color (anthraquinone) and bioluminescence on the deterrence of insect scavengers. Our data shows that scavenger deterrent factor (SDF) is not related to red cadaver coloration or bioluminescence activity as crickets and ants did not consume Galleria mellonella cadavers infected by P. laumondii strain 48-02 and X. bovienii. Both bacteria exhibit SDF activity but do not produce anthraquinone. Also, the insects were not affected by anthraquinone in agar plugs prepared with supernatant from induced P. laumondii Δpptase Pcep-KM-antA (SVS-275) mutant strain, which overproduces anthraquinone. Since bioluminescence and anthraquinone are not responsible for SDF activity against insect scavengers, more studies are needed to elucidate the SDF compound from Xenorhabdus and Photorhabdus bacteria. [ABSTRACT FROM AUTHOR]

[Display omitted] • Larvicidal and ovidical activities of bacterial CFS are dose and species dependent. • Xenorhabdus bacterial metabolites have ovicidal effects on Aedes aegypti eggs. • Fabclavines are highly toxic against mosquito larvae. Aedes -transmitted arboviral infections such as Dengue, Yellow Fever, Zika and Chikungunya are increasing public health problems. Xenorhabdus and Photorhabdus bacteria are promising sources of effective compounds with important biological activities. This study investigated the effects of cell-free supernatants of X. szentirmaii , X. cabanillasii and P. kayaii against Ae. aegypti eggs and larvae and identified the bioactive larvicidal compound in X. szentirmaii using The EasyPACId method. Among the three tested bacterial species, X. cabanillasii exhibited the highest (96%) egg hatching inhibition and larvicidal activity (100% mortality), whereas P. kayaii was the least effective species in our study. EasyPACId method revealed that bioactive larvicidal compound in the bacterial supernatant was fabclavine. Fabclavines obtained from promoter exchange mutants of different bacterial species such as X. cabanillasii, X. budapestensis, X. indica , X. szentirmaii, X. hominckii and X. stockiae were effective against mosquito larvae. Results show that these bacterial metabolites have potential to be used in integrated pest management (IPM) programmes of mosquitoes. [ABSTRACT FROM AUTHOR]

[Display omitted] • -Selenium nanoparticles (XC-SeNPs) were fabricated using cell free extract of Xenorhabdus cabanillasii. • Mosquito larvicidal activity of the XC-SeNPs were assessed against the 4th-instar Ae. aegypti. • XC-SeNPs displayed a dose-dependent larvicidal effect. • -The larval mortality was ranged between 13 and 72% depending XC-SeNPs concentration. • -The LC 50 and LC 90 concentration of XC-SeNPs were 79.49 and 722.45 ppm, respectively. Nanomaterials are successful due to their numerous applications in various domains such as cancer treatment, environmental applications, drug and gene delivery. Selenium is a metalloid element with broad biological activities and low toxicity especially at the nanoscale. Several studies have shown that nanoparticles synthesized from microbial and plant extracts are effective against important pests and pathogens. This study describes the bio fabrication of selenium nanoparticles using cell free extract of Xenorhabdus cabanillasii (XC-SeNPs) and assessed their mosquito larvicidal properties. Crystallographic structure and size of XC-SeNPs were determined with UV-a spectrophotometer, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), Energy-dispersive X-ray spectroscopy (EDAX), Zeta potential and Transmission electron microscopy (TEM). The significant surface plasmon resonance at 275 nm indicated the synthesis of XC-SeNPs from the pure cell-free extract of X. cabanillasii. The XRD result exhibits the crystalline nature of XC-SeNPs. The Zeta potential analysis confirmed that the surface charge of XC-SeNPs was −24.17 mV. TEM analysis revealed that synthesized XC-SeNPs were monodispersed, spherically shaped, and sized about 80–200 nm range. In addition, the larvicidal potentials of the bio-fabricated XC-SeNPs were assessed against the 4th-instar Ae. aegypti. XC-SeNPs displayed a dose-dependent larvicidal effect; the larval mortality was 13.3 % at the minimum evaluated concentration and increased to 72 % at higher dose treatments. The LC 50 and LC 90 concentration of XC-SeNPs against mosquito larvae were 79.4 and 722.4 ppm, respectively. [ABSTRACT FROM AUTHOR]

• Bacterial metabolites of Xenorhabdus enter Tetranychus urticae adults through cuticle. • Predatory mites were less affected by the bacterial metabolites than T. urticae. • Eggs of predatory mites were resistant to X. szentirmaii or X. nematophila supernatant. • Bacterial supernatants killed 18.5%-39.2% of mobile stages of predatory mites. • Long legs and thick cuticle of predatory mites reduce their contact with metabolites. The bacterial metabolites in supernatants of Xenorhabdus species have acaricidal activity, but this mode of entry into mites has not yet been elucidated. Herein, we report on the possible mode of entry of Xenorhabdus szentirmaii and Xenorhabdus nematophila supernatants into Tetranychus urticae (Acari: Tetranychidae) adult females. We also assessed the toxicity of the supernatants against the developmental stages of the predatory mites, Phytoseiulus persimilis and Neoseiulus californicus (Acari: Phytoseiidae). Experiments were conducted at 25 ± 1 °C, 70 ± 5% relative humidity, and 16:8h light:dark conditions. Our data showed that the bioactive acaricidal compound is most effective (86.5 to 89% mortality) when the entire integument of T. urticae comes in contact with it compared to contact of the ventral side only (26.5–34%). Against P. persimilis and N. californicus at 6 days post-application (dpa), the eggs were not affected by the X. szentirmaii or X. nematophila supernatant, whereas mortality of the mobile stages (larva, protonymph, deutonymph, adult) was 18.5% to 39.2%. Overall, the predatory mites were less affected by the bacterial metabolites than T. urticae. We hypothesize that the differences in morphology such as longer legs and thicker cuticle, as well as the diet of the predatory mites, reduce the contact of the body parts to the supernatant-treated surfaces. We need to isolate, identify, and characterize the X. szentirmaii and X. nematophila metabolite(s) and demonstrate efficacy to pestiferous mites and safety to plants, non-target organisms and the environment before it can be used as an acaricide. [ABSTRACT FROM AUTHOR]

[Display omitted] • Insecticides have no significant effect on the survival and virulence of the infective juveniles. • Steinernema carpocapsae IJs were not repulsed by pesticides in insect cadavers when scavenging. • More IJs invaded cypermethrin and Spinosad-killed host than diflubenzuron-killed and freeze-killed control. • The fitness of scavenging IJs is not diminished by insecticides in insect cadavers. • In some cases, the exposure to chemical insecticides may enhance virulence of scavenging nematodes. Entomopathogenic nematodes are used widely in biological insect control. Entomopathogenic nematodes can infect live insects as well as dead insects (i.e., they can act as scavengers). It is important to determine compatibility of entomopathogenic nematodes with other pest management tactics such as chemical insecticides. We hypothesized that chemical insecticides have negative impact on scavenging nematodes. According to our hypothesis, we first investigated the effects of direct exposure of Steinernema carpocapsae infectivity juveniles (IJs) to three chemical insecticides, cypermethrin, spinosad or diflubenzuron in terms of nematode survival and virulence. Subsequently, using the same chemicals, we tested the effects of insecticide-killed insects on scavenger nematode penetration efficiency, time of emergence and the number of nematode progeny. Prior to our study, the impact of pesticides on scavenger nematode fitness had not been studied. Fall webworm, Hyphantria cunea, and greater wax moth, Galleria mellonella, larvae were used as host insects. The survival rate of IJs after direct exposure was 83% for cypermethrin and 93–97% for the other insecticides and control. There were no significant differences in the survival and virulence of the nematodes after 24 h exposure to insecticides. The number of nematodes that invaded the insecticide-killed host was significantly higher in cypermethrin and spinosad treated groups and live H. cunea than in the diflubenzoron treated group and freeze-killed control. However, no significant differences were observed in time of emergence. Significantly more progeny IJs emerged from Spinosad-killed insects than the freeze-killed control. In conclusion, we discovered that the fitness of scavenging IJs is not diminished by insecticides in insect cadavers. In fact, in some cases the exposure to chemical insecticides may enhance virulence. [ABSTRACT FROM AUTHOR]

• Metarhizium VOCs, 1-octen-3-ol and 3 octanone, influence behaviour of EPN. • High doses of 1-octen-3-ol and 3 octanone repel or kill EPN infective juveniles. • Metarhizium volatiles reduce EPN infectivity of insect hosts. • Metarhizium VOCs immobilise or kill insects. • Volatiles affect reproduction of EPN inside host. The entomopathogenic fungus (EPF) Metarhizium brunneum occupies the same ecological niche as entomopathogenic nematodes (EPN), with both competing for insects as a food source in the rhizosphere. Interactions between these biocontrol agents can be antagonistic or synergistic. To better understand these interactions, this study focussed on investigating the effect of M. brunneum volatile organic compounds (VOCs), 1-octen-3-ol and 3-octanone, on EPN survival and behaviour. These VOCs proved to be highly toxic to the infective juveniles (IJs) of the EPN Steinernema carpocapsae , Steinernema feltiae and Heterorhabditis bacteriophora with mortality being dose dependent. Chemotaxis studies of H. bacteriophora IJs in Pluronic F127 gel revealed significant preference for the VOCs compared with controls for all tested concentrations. The VOCs also impacted on the test insects in a dose-dependent manner with 3-octanone being more toxic to Galleria mellonella , Cydia splendana and Curculio elephas larvae than 1-octen-3-ol. Mortality of C. splendana and G. mellonella larvae was significantly higher when exposed to relatively high doses (>25%) of 3-octanone. Lower doses of 3-octanone and 1-octen-3-ol immobilised test insects, which recovered after exposure to fresh air for 2 hrs. In depth studies on H. bacteriophora showed that exposure of IJs to > 10% concentration of 3-octanone or 1-octen-3-ol negatively affected infectivity whereas exposure to lower doses (0.1%, 0.01%) had no effect. The VOCs affected IJs, reducing penetration efficacy and the number of generations inside G. mellonella but they failed to inhibit the bacterial symbiont, Photorhabdus kayaii. The ecological significance of VOCs and how they could influence EPF-EPN insect interactions is discussed. [ABSTRACT FROM AUTHOR]

• Entomopathogenic nematodes (EPNs) in soil are attacked by natural enemies. • Bacteria, fungi, mites and collembolans are major mortality factors of EPNs in soil. • Deterrent compounds are produced by symbiotic bacteria of EPNs. • The compounds protect the nematode-killed insects from microbial invasion. • The compounds also protects nematode-killed insects from omnivores and scavengers. Entomopathogenic nematodes (EPNs) in the families Steinernematidae and Heterorhabditidae are effective biocontrol agents against a number of important soil insect pests and are safe to vertebrates, plants and other non-target organisms with no negative effects on the environment. They are associated with mutualistic bacteria in the genus Xenorhabdus for Steinernematidae and Photorhabdus for Heterorhabditidae and are often referred to as the nematode/bacterium complex. The natural habitat of EPNs is the soil where the third-stage infective juveniles (IJs), the only free-living stage, can infect an array of insect hosts. However, the survival of the IJs is affected by various abiotic (i.e., temperature, moisture, soil texture, soil salinity, UV light, oxygen, and pH) and biotic (i.e., natural enemies, omnivores, scavengers, competitors, and plants) factors in the soil. In this review, we summarize the impact of the biotic factors, especially natural enemies, omnivores, scavengers, and competitors against EPNs and conclude that the major predators of the IJs appear to be nematophagous fungi, mites, and collembolans. Omnivores and scavengers, particularly, mites, collembolans, ants and birds, feeding on EPN-killed insects appear to be the major mortality factors on the developing nematodes especially of insects that are 2 days or less post infection. In addition, we discuss the defense mechanisms of EPN IJs against nematophagous fungi, and the protection of the nematode-killed insects by production of the scavenger deterrent factor produced by the mutualistic bacteria against omnivores and scavengers. By understanding the interactions between EPNs and their antagonists we can improve and increase the successful use of EPNs in biological control programs. [ABSTRACT FROM AUTHOR]

• Sponges are used in the formulation of mass-produced nematodes. • Sponges are employed in laboratories to store nematodes or to transport them from one laboratory to another. • Different sponge types have different effects on the survival and infectivity of stored nematodes. • Polyurethane, melamine, and cellulose sponges were the best for nematode storage. • Oasis floral sponge can be preferred for short-term IJ formulation and storage for field applications. Sponges are one of the cheapest and most suitable substrates used to formulate and/or store the infective juveniles (IJs) of entomopathogenic nematodes (EPNs). Our study investigated the survival and infectivity of the IJs on five different sponges compared to that in an aqueous suspension (control). The sponges were Oasis® floral, Nanosponge, ScotchbriteTM, or Lysol® and natural sea sponge. EPN species tested were Heterorhabditis bacteriophora, Steinernema carpocapsae and S. feltiae. The recovery efficiency of the IJs from sponges was initially assessed. Subsequently, IJs were stored in the sponges and placed in plastic bags or Falcon tubes and incubated at 10° or 27 °C for 8 months or 11 weeks, respectively. IJ survival and infectivity were monitored monthly for the 10 °C and weekly for 27 °C in these sponge types. The IJs were recovered from the sponges, and their survival was based on observing their movement under a dissecting microscope, and infectivity was based on larval mortality in Galleria mellonella. Recovery efficiency of IJs was best for the Oasis floral sponge for all nematode species ranging between 83 and 91%. The survival and infectivity of stored IJs in all sponge types and control for both 10° and 27 °C gradually decreased over time. IJs stored in Scotchbrite, Lysol, and Nanosponge had the best survival and infectivity, whereas Oasis floral and natural sea sponges showed the poorest results. After 8 months at 10 °C in plastic bags, the survival ratio of all IJs in these three sponges (Scotchbrite, Lysol, and Nanosponge) was approximately 55%. IJs in Scotchbrite and Nanosponge were also able to survive and retain their infectivity at 27 °C for 3 months. IJs stored in Falcon tubes had survival that ranged from 26 to 53% at 27 °C and 55 to 77% at 10 °C. H. bacteriophora IJs lost their infectivity when stored at 27 °C after 10 weeks. However, S. carpocapsae and S. feltiae exhibited 85% infectivity when stored in Scotchbrite and 50% in Nanosponge, respectively. Overall, sponges made from polyurethane (Scotchbrite) followed by melamine (Nanosponge) and cellulose (Lysol) are recommended for long-term nematode storage and transportation of nematode samples. However, Oasis floral sponge may be preferred for short-term IJ formulation for field applications because of easier recovery of IJs. [ABSTRACT FROM AUTHOR]