Beneficial worm allies warn plants of parasite attack below-ground and reduce above-ground herbivore preference and performance.

Antagonistic interactions among different functional guilds of nematodes have been recognized for quite some time, but the underlying explanatory mechanisms are unclear. We investigated responses of tomato (Solanum lycopersicum) to two functional guilds of nematodes-plant parasite (Meloidogyne javanica) and entomopathogens (Heterorhabditis bacteriophora, Steinernema feltiae below-ground, and S. carpocapsae)-as well as a leaf mining insect (Tuta absoluta) above-ground. Our results indicate that entomopathogenic nematodes (EPNs): (1) reduced root knot nematode (RKN) infestation below-ground, (2) reduced herbivore (T. absoluta) host preference and performance above-ground, and (3) induced overlapping plant defence responses by rapidly activating polyphenol oxidase and guaiacol peroxidase activity in roots, but simultaneously suppressing this activity in above-ground tissues. Concurrently, we investigated potential plant signalling mechanisms underlying these interactions using transcriptome analyses. We found that both entomopathogens and plant parasites triggered immune responses in plant roots with shared gene expression. Secondary metabolite transcripts induced in response to the two nematode functional guilds were generally overlapping and showed an analogous profile of regulation. Likewise, we show that EPNs modulate plant defence against RKN invasion, in part, by suppressing active expression of antioxidant enzymes. Inoculations of roots with EPN triggered an immune response in tomato via upregulated phenylpropanoid metabolism and synthesis of protease inhibitors in plant tissues, which may explain decreased egg laying and developmental performance exhibited by herbivores on EPN-inoculated plants. Furthermore, changes induced in the volatile organic compound-related transcriptome indicated that M. javanica and/or S. carpocapsae inoculation of plants triggered both direct and indirect defences. Our results support the hypothesis that plants "mistake" subterranean EPNs for parasites, and these otherwise beneficial worms activate a battery of plant defences associated with systemic acquired resistance and/or induced systemic resistance with concomitant antagonistic effects on temporally co-occurring subterranean plant pathogenic nematodes and terrestrial herbivores.

Whole-genome-based revisit of Photorhabdus phylogeny: proposal for the elevation of most Photorhabdus subspecies to the species level and description of one novel species Photorhabdus bodei sp. nov., and one novel subspecies Photorhabdus laumondii subsp. clarkei subsp. nov.

Bacterial symbionts are crucial for the infectivity and success of entomopathogenic nematodes as biological control agents. The current understanding of the symbiotic relationships is limited by taxonomic uncertainties. Here, we used whole-genome sequencing and traditional techniques to reconstruct the phylogenetic relationships between all described Photorhabdus species and subspecies as well as 11 newly isolated symbiotic bacteria of Heterorhabditis nematodes, including the unreported bacterial partner of H. beicherriana. In silico DNA-DNA hybridization, orthologous average nucleotide identity and nucleotide sequence identity of concatenated housekeeping genes scores were calculated and set into relation with current cut-off values for species delimitation in bacteria. Sequence data were complemented with biochemical and chemotaxonomic markers, and ribosomal protein fingerprinting profiles. This polyphasic approach resolves the ambiguous taxonomy of Photorhabdusand lead to the proposal for the elevation of most of them into a higher taxon and the creation of several new taxa: 15 new species, one of which is newly described: Photorhabdus bodei sp. nov. (type strain LJ24-63T=DSM 105690T=CCOS 1159T) and the other 14 arise through the proposal of elevating already described subspecies to species, and are proposed to be renamed as follows: Photorhabdus asymbioticasubsp. australis as Photorhabdus australis sp. nov., Photorhabdus luminescenssubsp. akhurstii as Photorhabdus akhurstii sp. nov., Photorhabdus luminescenssubsp. caribbeanensis as Photorhabdus caribbeanensis sp. nov., Photorhabdus luminescenssubsp. hainanensis as Photorhabdus hainanensis sp. nov., Photorhabdus luminescenssubsp. kayaii as Photorhabdus kayaii sp. nov., Photorhabdus luminescenssubsp. kleinii as Photorhabdus kleinii sp. nov., Photorhabdus luminescenssubsp. namnaonensis as Photorhabdus namnaonensis sp. nov., Photorhabdus luminescenssubsp. noenieputensis as Photorhabdus noenieputensis sp. nov., Photorhabdus luminescenssubsp.laumondii as Photorhabdus laumondii sp. nov., Photorhabdus temperatasubsp. cinerea as Photorhabdus cinerea sp. nov., Photorhabdus temperatasubsp. khanii as Photorhabdus khanii sp. nov., Photorhabdus temperatasubsp. stackebrandtii as Photorhabdus stackebrandtii sp. nov., Photorhabdus temperatasubsp. tasmaniensis as Photorhabdus tasmaniensis sp. nov., and Photorhabdus temperatasubsp. thracensis as Photorhabdus thracensis sp. nov. In addition, we propose the creation of two new subspecies, one of which arises through the reduction of rank: Photorhabdus laumondii subsp. laumondii comb. nov. (basonym: P. luminescenssubsp. laumondii) and the second one is newly described: Photorhabdus laumondii subsp. clarkei subsp. nov. (type strain BOJ-47T=DSM 105531T=CCOS 1160T). Finally, we propose to emend the description of three species, which results from the proposal of elevating three subspecies to the species status: Photorhabdus asymbiotica, Photorhabdus temperata and Photorhabdus luminescens, formerly classified as Photorhabdus asymbioticasubsp. asymbiotica, Photorhabdus temperatasubsp.temperata and Photorhabdus luminescenssubsp. luminescens, respectively.

New Insight into the Management of the Tomato Leaf Miner, Tuta absoluta (Lepidoptera: Gelechiidae) with Entomopathogenic Nematodes.

The tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is a serious threat to tomato production in the world. Due to serious issues with insecticide resistance, there is a dire need for alternative control methods. Entomopathogenic nematodes (EPN) have potential for the biological control of T. absoluta. In the laboratory, we examined the effect of temperature, soil type, and exposure time on the efficacy of the EPN species Steinernema carpocapsae (Nematoda: Steinernematidae) and Heterorhabditis bacteriophora (Nematoda: Heterorhabditidae) against last-instar T. absoluta larvae. Both species caused high mortality in loamy sand (89%) and coco peat (93%) but not in sandy loam (17%). H. bacteriophora caused 92-96% mortality at 19, 25, and 31°C; S. carpocapsae caused 89-91% mortality at 25 and 31°C but only 76% at 19°C. Both species caused similar mortality levels after 65-min exposure; thereafter, mortality increased only with S. carpocapsae reaching high levels even at a low concentration. Both species infected larvae within leaf galleries. When applied to whole large tomato plants in the greenhouse, both species provided similar control levels (48-51%) at high pest densities. Both species could be incorporated as an effective alternative to synthetic insecticides into T. absoluta management programs in greenhouse tomato production.

Are Entomopathogenic Nematodes Effective Biological Control Agents Against the Carob Moth, Ectomyelois ceratoniae?

The carob moth (Ectomyelois ceratoniae) is the key pest of pomegranate, which causes a significant percentage of losses in pomegranate orchards and warehouses of Iran annually. The pest larvae are characterized by displaying a cryptic behavior within the fruit, which avoids most routine control techniques, especially chemical method. The low efficiency of traditional measurements and also the rich species diversity of natural enemies within the infested fruits highlight the necessity of exploring effective control methods, especially environmental friendly approaches. Entomopathogenic nematodes (EPNs) are a group of biological control agents that actively search for the host, including those in a cryptic habitat like the carob moth larvae within infested fruits. Here, we assumed that treatment of the infested and dropped fruits with EPNs may provide new insight into the management of the carob moth. Three species of EPNs, Steinernema feltiae, S. carpocapsae, and Heterorhabditis bacteriophora were selected and used in a series of in vitro and in vivo experiments. In preliminary assays, the EPNs species were used with different concentrations of infective juveniles (IJs) (0, 1, 5, 10, 25, and 50 IJ/larvae) in 2-cm diam. plates. The mortality rates of the laboratory tests were 79.75% and 76.5% for S. feltiae and S. carpocapsae, corresponded to LC50 value of 2.02 IJ/larva for S. feltiae and 2.05 IJ/larva for S. carpocapsae. On the contrary, H. bacteriophora demonstrated low virulence on the pest larvae in petri tests with a LC50 = 426.92 IJ/larva. Hence, both Steinernema species were selected for subsequent experiments. The penetration rate for S. feltiae and S. carpocapsae into the hemocoel of the pest was 43% and 31%, respectively, and the corresponding reproduction rate was 15,452 IJ/larva for S. feltiae and 18,456 IJ/larva for S. carpocapsae. The gathered data from those in vitro tests were used for a field assay. Different concentrations (5, 10, 50, 100, and 160 IJ/cm2 of the arena) of S. feltiae and S. carpocapsae were applied in the field test. The mean mortality results from the last test were 10.89% and 26.65% for S. feltiae and S. carpocapsae, respectively. Finally, we found that these low virulence rates of the nematodes were attributed to inhibitory/repellency effects of saprophytic fungi within the infested pomegranates, a usual status of the infested fruits in autumn or winter seasons. Future work on additional EPN populations more adapted to the extreme conditions of the pomegranate production area in Iran may provide sufficient evidence to continue the further investigation on the best EPN species populations and advanced formulations with high durability.