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On the basis of biological activities of the ethyl acetate extracts of four Xenorhabdus sp., including Xenorhabdus nematophila FUM 220, Xenorhabdus nematophila FUM 221, Xenorhabdus bovienii FUM 222, and Xenorhabdus bovienii FUM 223, X. nematophila FUM 220 was preferentially selected to track the isolation of responsible compounds. Chemical study on the ethyl acetate extract of X. nematophila isolate FUM220 which is derived from the native nematode Steinernema carpocapsae (Rhabditida: Steinernematidae), was evaluated, and eleven compounds, including xenocoumacin II (1), xenortide-396 (2), xenortide A (3), xenortide-410 (4), xenortide-449 (5), xenematide A 663 (6), rhabdopeptide-574 (7), rhabdopeptide-588 (8), rhabdopeptide-687 (9), rhabdopeptide-701 (10), and nematophin-273 (11) were characterized. In this experimental study, we surveyed the antitumoral potential of bacterial extract and bacterial metabolites to treat human breast cancer (MCF-7), human lung cancer (A549), and murine Tumor (B16) cell lines. We observed that all samples were cytotoxic, but bacterial extracts of X. nematophila FUM 220 and X. bovienii FUM 223 showed higher toxicity on mentioned cell lines. Potent cytotoxic activity was found for compounds 6 and 11 with IC50 of 6.2 μg/ml against human lung cancer A549 cell lines, too. These compounds showed moderated antibacterial activity against Xanthomonas oryzae pv. oryzae strain Xoo-IR42 (Xanthomonadales: Xanthomonadaceae) (MIC of 62.5 μg/ml) and Staphylococcus aureus strain 1112 (Bacillales: Staphylococcaceae) (MIC of 100 μg/ml). The bacterial extracts from X. bovienii FUM 222 showed strong inhibition of the growth of S. aureus strain 1112, by a minimal inhibitory concentration assay (MIC of 53.5 μg/ml). Xenorhabdus genera produce metabolites with potent cytotoxic and antibacterial activity. Single compounds can be isolated, identified, and commercialized, but various species or strains may change their anticancer or antimicrobial potential. The present study brings new clues regarding the qualified of Xenorhabdus as future peptide sources for supplying natural bioactive compounds and challenge multidrug-resistant bacteria, treat cancer, and plant diseases.

Soil as a shared habitat of white grubs and entomopathogenic nematodes (EPNs) is a double-edged sword from the biological control point of view. Soil encompasses a diverse array of EPNs that could be exploited in grub microbial control; on the other hand, soil promotes the natural resistance of grubs to EPNs via the battle between both sides within the soil matrix. White grubs and EPNs have been armed in this battle by a multifaceted range of mechanisms, namely grub structural and physiological barriers, antagonism of grub gut microbiota toward the nematode bacterial symbionts, EPN excreted/secreted proteins, surface coat proteins, ascaroside pheromones produced by EPNs, and evolution of EPN resistance to herbivore self-defense. From the evolutionary point of view, EPN–grub interactions, the most advanced (sophisticated) association among others, could have evolved from other types of associations. Entomophilic nematode (e.g., Pristionchus spp.), the cognate bacterium and scarab associations along with the formation of dauer juveniles, are proof of preadaptation to entomopathogeny in a continual evolution. Here, we delve into the salient features of each component of EPN-white grub–host plant tripartite interactions as well as hints to improved exploitation of EPNs for grub management. Also, evolutionary associations between nematodes and scarabs will be reviewed, in short.

The infectivity of three species of entomopathogenic nematodes (EPNs) such as Steinernema carpocapsae Weiser (Rhabditida: Steinernematidae), Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae), and H. bacteriophora Poinar (IRQ.1 strain) were examined against subterranean termite Microcerotermes diversus (Silvestri) (Blattodea: Termitidae) that is the most economically destructive termite in Iraq. Laboratory and field efficacy of these strains were evaluated to test the feasibility of indigenous EPNs to be used in a biological control program. The biological traits examined included pathogenicity, penetration, and reproduction of EPN species. Filter paper and wood bioassays were conducted using six concentrations: 25, 50, 100, 200, 400, and 600 IJs/termite. In both tests, all strains were virulent against M. diversus workers. The LC50 of S. carpocapsae in both petri dishes and in containers with sawdust was (57.9 and 15.7 IJs/termite) less than both indigenous (274.2 and 60.8 IJs/termite) and commercial (139.6 and 52.6 IJs/termite) Heterorhabditis bacteriophora, respectively. In the field, the percent mortality of the tested workers ranged from 22.5–80 ± 8.3%, 37.5–96.2 ± 8.9%, and 28.7–67.5 ± 6.8% for commercial H. bacteriophora and S. carpocapsae and native H. bacteriophora, respectively. All EPN strains successfully penetrated the M. diversus workers under field conditions, while the results showed that there was a significant difference between the three EPN strains. The percent mortality caused by native H. bacteriophora against termites was higher (43.6 ± 2.7%) than both commercial strains of S. carpocapsae (36.9 ± 1.6%) and H. bacteriophora (29.9 ± 1.4 %). These results highlight the efficiency of EPNs for the control of M. diversus workers.

The attraction of entomopathogenic nematodes (EPNs) to herbivore-injured plant roots has been documented recently to be a common tritrophic interaction. Belowground tritrophic interactions are especially subject to modulation by many abiotic factors including drought. In this study, complementary greenhouse experiments were conducted to understand how drought stress might affect a potato plant’s impact on EPN behavior. In separate trials, the responses of the EPN Steinernema diaprepesi (Nguyen and Duncan) (Rhabditida: Steinernematidae) to root herbivory by larvae of the weevil Diaprepes abbreviatus (Linnaeus) (Coleoptera: Curculionidae), in well-watered and drought stressed potato plants, were measured using soil-matrix olfactometers with two arms. The drought treatments were initiated in 30-d old plants. Drought-stressed potato plants received water when potentiometers read approximately 20 kPa, while for well-watered plants, the number was 8 kPa. Four weeks after initiating the treatments, 400 ml water was added to all pots, immediately before starting the experiments. The experiments revealed that S. diaprepesi infective juveniles (IJs) did not migrate preferentially toward drought-stressed or well-watered plants when neither were subjected to herbivory [t(21) = 1.13, P = 0.269]. However, plants with roots damaged by herbivory attracted more S. diaprepesi IJs if they were well watered than if they were drought stressed [t(24) = 3.19, P = 0.004]. If both plants in the olfactometers were drought stressed, EPNs moved preferentially toward those with root herbivory than those with undamaged roots [t(23) = 3.19, P = 0.004]. No difference was detected in gas chromatography profiles between droughted and well-watered plant roots subjected to herbivory [F(24, 336) = 0.68, P = 0.87]. GC analysis showed that three compounds, including 3-nonanone [t(6) = 4.83, P = 0.003], artemisyl ketone [t(7) = 6.21, P = 0.000], and benzoic acid, 4-ethoxy-, ethyl ester [t(7) = −4.22, P = 0.004] were significantly higher in drought stressed than control plant roots. These results indicate that potatoes, like other plants, can recruit EPNs in response to root herbivory, and that drought stress dampens this tritrophic interaction where choice is involved. Additional research that resolves the mechanisms of these interactions may provide insights to exploit EPNs for crop protection.

Molecular genetics and symbiont diagnostics have revolutionized our understanding of insect species diversity, and the transformative effects of bacterial symbionts on host life history. Encarsia inaron is a parasitoid wasp that has been shown to harbour two bacterial endosymbionts, Wolbachia and Cardinium. Known then as E. partenopea, it was introduced to the USA in the late 1980s from populations collected in Italy and Israel for the biological control of an ornamental tree pest, the ash whitefly, Siphoninus phillyreae. We studied natural populations from sites in the USA, the Mediterranean and the Middle East as well as from a Cardinium-infected laboratory culture established from Italy, with the aims of characterizing these populations genetically, testing reproductive isolation, determining symbiont infection status in their native and introduced range, and determining symbiont role. The results showed that the two Encarsia populations introduced to the USA are genetically distinct, reproductively isolated, have different symbionts and different host-symbiont interactions, and can be considered different biological species. One ('E. inaron') is doubly infected by Wolbachia and Cardinium, while only Cardinium is present in the other ('E. partenopea'). The Cardinium strains in the two species are distinct, although closely related, and crossing tests indicate that the Cardinium infecting 'E. partenopea' induces cytoplasmic incompatibility. The frequency of symbiont infection found in the native and introduced range of these wasps was similar, unlike the pattern seen in some other systems. These results also lead to a retelling of a successful biological control story, with several more characters than had been initially described.

Aphidiinae (Braconidae: Aphidiinae) is a subfamily of endoparasitic wasps specialized in parasitizing aphids. Although, to date, different methods have been used to measure parasitism level, obtaining an accurate estimate remains challenging due to several limiting factors. This study was set to: 1) Compare efficiency of conventional and molecular-based methods in estimating parasitism level of the pomegranate aphid Aphis punicae (Passerini; Hemiptera: Aphididae), and 2) Estimate seasonal activity of the Aphidiinae parasitoids of the pomegranate aphid. The molecular approach (polymerase chain reaction [PCR]) detected the presence of three main parasitoids Lysiphlebus fabarum (Marshal; Hymenoptra: Braconidae), Binodoxys angelicae (Haliday; Hymenoptra: Braconidae), and Ephedrus persicae (Frogatt; Hymenoptra: Braconidae). The presence of hyperparasitoid and aphid DNAs did not interfere with the outcome, indicating specificity of the selected primers. Minimum concentrations of DNA needed for successful amplifications were 16.33, 28.65, and 22.65 ng µl−1, for L. fabarum, B. angelicae, and E. persicae, respectively. The level of parasitism was significantly higher in spring (28.42%) than both summer and fall; parasitism level during summer (11.89%) and fall (5.86%) formed a homogeneous statistical subset. Although the overall level of parasitism estimated by PCR (22.7%) was more than twofold higher than those estimated by a conventional counting method (10.5%), there was a strong positive correlation between the two approaches. Provided the potential limitations of either method, simultaneous use of both methods was recommended for an objective estimate of the effectiveness of the Aphidiinae parasitoids as biological control agents of A. punicae.