Plant nutritional quality is dependent on soil nutrients and co-evolved soil microbial symbionts. Most plants associate with arbuscular mycorrhizal (AM) fungi, which alter their nutritional quality ...and silicon (Si) uptake from the soil. High Si concentrations reduce plant nutritional quality and can act as an effective defence both aboveground and belowground. The growth and immune function of insect herbivores is dependent on the quality of their host plants, hence the AM symbiosis and Si concentrations can impact insect growth and immunity via changes in host plant quality. The effects of AM fungi or Si on root herbivores are poorly quantified, while impacts on insect immunity are unknown. We investigated the effects of host plant colonisation by AM fungi and high root Si concentrations on plant quality alongside the growth of a root feeding insect and the immune response to entomopathogenic nematode infection.
Two sugarcane varieties (Saccharum species hybrids L.) were grown under fully factorial treatment combinations of ± Si and AM/non-AM. Root feeding insects (Dermolepida albohirtum Waterhouse) fed on the plants and their immune function was assessed in a bioassay, while insect growth and root consumption were assessed in a feeding trial. We found high Si concentrations decreased insect growth and root consumption, the latter by 71%. Insect growth was reduced on plants associated with AM fungi, which was dependent on Si treatment and plant variety. Insect immunity increased by 62% on AM colonised plants, which negatively correlated with insect growth. These results demonstrate that the impacts of the AM symbiosis on root feeding insects can depend on Si availability and plant variety. Our study suggests that AM fungi can prime insect immunity, independent of host plant quality or Si concentrations, and the negative effects of AM fungi on soil dwelling insects involves immune function stimulation which, due to a growth-immunity trade-off, results in growth reduction.
•Silicon (Si) application increased plant growth and decreased insect performance.•Arbuscular mycorrhizal (AM) fungi increase root Si which reduced insect growth.•Effects of the AM symbiosis on insect growth was dependent on plant variety.•The AM symbiosis increased insect immunity, independent of plant quality.•A growth-immunity trade off may explain insect responses to AM colonised plants.
•The cabbage stem flea beetle is an economically important pest of oilseed rape.•Control using only conventional insecticides often ineffective.•Entomopathogens and natural enemies are potentially ...effective biocontrol agents.•Additional research needed to create integrated pest management programs.•Research gaps: need to understand interactions between agents to optimize control.
The cabbage stem flea beetle (CSFB11CSFB: cabbage stem flea beetle.) Psylliodes chrysocephala Linnaeus is the most important pest of oilseed rape (Brassica napus) crops in Europe. Control has become more difficult since the European Union ban in 2013 on the use of neonicotinoid seed treatments. This situation is made more challenging by the development of resistance to pyrethroid insecticides, the only remaining conventional synthetic insecticides with which to control CSFB.
The purpose of this paper is to review the potential of biological alternatives to the use of synthetic pesticides for the control of the CSFB. Only a small number of studies have investigated biological control agents against CSFB itself. More research has, however, been published on two other, closely related chrysomelid pests of brassica crops that have similar life cycles, namely the crucifer flea beetle Phyllotreta cruciferae and the striped flea beetle Phyllotreta striolata, which enable us to extrapolate reasonably across to CSFB. The biological control agents investigated include entomopathogenic fungi (EPF22EPF: entomopathogenic fungi.) such as Metarhizium anisopliae and Beauveria bassiana, entomopathogenic nematodes (EPN33EPN: entomopathogenic nematode.) such as Steinernema feltiae and Steinernema carpocapsae, parasitoids such as Microctonus brassicae and predators such as the ground beetle Trechus quadristriatus. Results vary depending on the setting (laboratory versus field), but several biological control agents investigated resulted in CSFB mortality greater than 50% under laboratory conditions. The biological control of the CSFB shows potential as a viable alternative to the use of conventional synthetic insecticides. Nonetheless, many research gaps remain, as current research has focused largely on crucifer flea beetle and striped flea beetle, with comparatively few studies investigating the potential of biological controls against the CSFB. The research published to date on CSFB has been limited to a small number of species of EPN and EPF with little work investigating the potential of parasitoids and predators. More field studies using EPF are required, while in contrast laboratory studies are underrepresented for EPN.
Further research is required, testing existing and new strains of fungi and nematodes, exploring the potential of endophytic fungi, enhancing the formulation and application of biological control for use in inundative strategies, and investigating the potential of conservation biological control. Effective biological control agents should ultimately be combined with cultural control methods in Integrated Pest Management (IPM44IPM: Integrated Pest Management.) systems for the sustainable management of this pest.
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•O. chongmingensis (Oc) has lower virulence to waxworms than S. carpocapsae (Sc).•Oc is more attracted to infected and freeze-killed insects than uninfected hosts.•Oc grows faster ...than Sc, including on primary and secondary phase X. nematophila.•The bacterial associate of Oc is antagonistic to the growth of X. nematophila.
Entomopathogenic nematodes (EPNs) continue to be explored for their potential usefulness in biological control and pest management programs. As more insect-associated species of nematodes are discovered and described, it is possible that scavengers and kleptoparasites may be mischaracterized as EPNs. If a nematode species is truly an entomopathogen it should display similar infectivity, as well as behaviors and preferences, to those of established EPN species, such as Steinernema carpocapsae. In this study we evaluated dauers of the putative EPN species Oscheius chongmingensis. We examined virulence, odor preferences as a measure of host-seeking behavior, and features of its bacterial symbiont Serratia nematodiphila. We determined that O. chongmingensis behaves more like a scavenger than an EPN. Not only did O. chongmingensis exhibit very poor pathogenicity in Galleria mellonella (wax moth larvae), it also displayed odor (host-seeking) preferences that are contrary to the well-known EPN S. carpocapsae. We also found that the bacterial symbiont of O. chongmingensis was antagonistic to S. carpocapsae; S. carpocapsae IJs were unable to develop when S. nematodiphila was a primary food source. We conclude that there is insufficient evidence to support the characterization of O. chongmingensis as an EPN; and based on the attributes of its preferences for already-infected or deceased hosts, suggest that this nematode is a scavenger, which may be on an evolutionary trajectory leading to an entomopathogenic lifestyle.
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•Nanoparticle stabilized Pickering emulsions (TPE and SPEG) were evaluated for protection against rapid desiccation (RD) of EPN IJs.•Both formulations significantly increased the ...timeline for survival and efficacy of EPN IJ.•Higher retention of surviving IJ in SPEG was observed in comparison to TPE and water.•LT50 of S. carpocapsae were increased from 14 hr in water to > 80, > 40 h by SPEG and TPE respectively at 24 °C & 77%RH.•Increased protection to IJ were observed at elevated temperatures & ultra-low humidity (34 °C & 52%RH).
Formulation technology has been the primordial focus to improve the low viability and erratic infectivity of entomopathogenic nematodes (EPNs) for foliar application. Adaptability to the fluctuating environment is a key trait in ensuring the survival and efficacy of EPNs. Hence, tailoring formulations towards EPNs foliar applications would effectively deliver consistent and reliable results for above-ground applications. EPNs survival and activity were characterized in novel Pickering emulsion post-application in planta cotton foliage. Two different types of novel formulations, Titanium Pickering emulsion (TPE) and Silica Pickering emulsion Gel (SPEG), were tailored for EPNs foliar applications. We report an extension of survival and infectivity to 96 hrs under controlled conditions by SPEG formulations for survival of IJ's on cotton foliage. In addition, survival of IJs (LT50) was extended from 14hrs in water to > 80 hrs and > 40 hrs by SPEG and TPE respectively. SPEG accounted for the slowest decrease of live IJs per surface area in comparison to TPE and control samples over time, exhibiting a 6-fold increase at 48 hrs. Under extreme conditions, survival and efficacy were extended for 8hrs in SPEG compared to merely 2hrs in control. Potential implications and possible mechanisms of protection are discussed.
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•Entomopathogenic nematodes (EPNs) can be powerful biocontrol agents of insect pests.•Infective juveniles face internal and environmental stresses while seeking for a host.•EPN ...abilities to cope with these stresses is crucial in determining their infectivity success.•The nematode model, C. elegans, provides valuable information on stress responses.•Understanding EPN stress tolerance is a promising avenue to engineer superior EPNs.
Entomopathogenic nematodes (EPNs) are soil-dwelling parasitic roundworms commonly used as biocontrol agents of insect pests in agriculture. EPN dauer juveniles locate and infect a host in which they will grow and multiply until resource depletion. During their free-living stage, EPNs face a series of internal and environmental stresses. Their ability to overcome these challenges is crucial to determine their infection success and survival. In this review, we provide a comprehensive overview of EPN response to stresses associated with starvation, low/elevated temperatures, desiccation, osmotic stress, hypoxia, and ultra-violet light. We further report EPN defense strategies to cope with biotic stressors such as viruses, bacteria, fungi, and predatory insects. By comparing the genetic and biochemical basis of these strategies to the nematode model Caenorhabditis elegans, we provide new avenues and targets to select and engineer precision nematodes adapted to specific field conditions.
Tannourine cedars forest, dominated by cedars (Cedrus libani, Richard), suffers from native sawfly attacks, Cephalcia tannourinensis (Chevin). The current study assesses the presence of ...entomopathogenic nematodes (EPNs) endemic to the forest for their potential use as biocontrol agents in an integrated pest management to control C. tannourinensis. A survey was conducted using Galleria mellonella baits in fifteen selected sites taking into consideration the cedars' different habitats. One EPN species, Steinernema feltiae, as determined by morphometric and molecular analyses, was found in one site in the forest and was tested under laboratory conditions against C. tannourinensis prepupae, causing a mortality of 64% at 250 Infective Juveniles (IJs)/prepupa. In light of previous studies, Heterorhabditis bacteriophora (commercial strain) was accordingly considered for the controlled in situ experiments where the pathogenicity of this EPN was evaluated on C. tannourinensis. A concentration of 625,000 IJs/m2 of H. bacteriophora caused a mortality rate of 85% on C. tannourinensis following inundative treatments conducted in jars buried in the forest's soil. While EPN succeeded to emerge from G. mellonella cadavers under the same conditions, no EPN emerged out of C. tannourinensis despite the high mortality percentage; also, opportunistic nematodes emerged unexpectedly out of C. tannourinensis cadavers.
Microbiome composition is frequently studied by the amplification and high-throughput sequencing of specific molecular markers (metabarcoding). Various hypervariable regions of the 16S rRNA gene are ...classically used to estimate bacterial diversity, but other universal bacterial markers with a finer taxonomic resolution could be employed. We compared specificity and sensitivity between a portion of the rpoB gene and the V3 V4 hypervariable region of the 16S rRNA gene.
We first designed universal primers for rpoB suitable for use with Illumina sequencing-based technology and constructed a reference rpoB database of 45,000 sequences. The rpoB and V3 V4 markers were amplified and sequenced from (i) a mock community of 19 bacterial strains from both Gram-negative and Gram-positive lineages; (ii) bacterial assemblages associated with entomopathogenic nematodes. In metabarcoding analyses of mock communities with two analytical pipelines (FROGS and DADA2), the estimated diversity captured with the rpoB marker resembled the expected composition of these mock communities more closely than that captured with V3 V4. The rpoB marker had a higher level of taxonomic affiliation, a higher sensitivity (detection of all the species present in the mock communities), and a higher specificity (low rates of spurious OTU detection) than V3 V4. We compared the performance of the rpoB and V3 V4 markers in an animal ecosystem model, the infective juveniles of the entomopathogenic nematode Steinernema glaseri carrying the symbiotic bacteria Xenorhabdus poinarii. Both markers showed the bacterial community associated with this nematode to be of low diversity (< 50 OTUs), but only rpoB reliably detected the symbiotic bacterium X. poinarii.
Our results confirm that different microbiota composition data may be obtained with different markers. We found that rpoB was a highly appropriate marker for assessing the taxonomic structure of mock communities and the nematode microbiota. Further studies on other ecosystems should be considered to evaluate the universal usefulness of the rpoB marker. Our data highlight two crucial elements that should be taken into account to ensure more reliable and accurate descriptions of microbial diversity in high-throughput amplicon sequencing analyses: i) the need to include mock communities as controls; ii) the advantages of using a multigenic approach including at least one housekeeping gene (rpoB is a good candidate) and one variable region of the 16S rRNA gene. This study will be useful to the growing scientific community describing bacterial communities by metabarcoding in diverse ecosystems.
Characterizing entomopathogenic nematode (EPN) biogeography with a goal of augmentation and conservation biological control requires fine-scale taxonomic resolution, because closely related EPN ...species can exhibit divergent phenotypes for key properties such as habitat adaptation and insect host specificity. Consequently, we employed high throughput genome sequencing (HTS) to identify and compare EPNs and natural enemies of EPNs in 58 citrus orchards in 2 ecoregions in Egypt (El Beheira and Al Qalyubia governorates). We designed improved primers targeting the ITS2 rDNA to discriminate EPN species and used pre-reported primers targeting D2-D3 region for soil microarthropods. Five EPN species (
,
,
,
, and
) and one steinernematid not represented in Genbank databases were detected. This is the first report of
and possibly the unknown (perhaps undescribed) species in Egypt. Only heterorhabditid species, dominated by
, were detected in the reclaimed, sandy desert soils of El Beheira governorate. In the fine textured, ancient farming lands of the Nile delta all six species were detected, but at lower frequency and abundance. Microarthropod family richness (
= 0.01) and abundance (
= 0.001) was higher in the reclaimed lands than in the Nile Delta. Soil clay content, pH and elevation explained significant variation in the mite community structure. Population density of
, the only EPN found consistently and at high abundance in El-Beheira, was inversely related to abundance of species in the nematophagous mite family Rhodacaridae.
The efficacy of various biological control agents and their application methods was tested against the root-knot nematodes Meloidogyne javanica and Meloidogyne incognita in large, in-ground tomato ...production areas. Treatments included infective juveniles (IJs) of the entomopathogenic nematode Steinernema feltiae, nematode-infected insect cadavers and cell-free supernatant of the nematode's bacterial symbiont (Xenorhabdus bovienii) and the nematode-parasitic fungus Purpureocillium lilacinum. The treatments were tested in two 1000 m2 greenhouses, one located in Fethiye and the other in Kepez Turkey. Galling index according to the Zeck scale, total yield and cost analyses were evaluated for each application method. The Zeck scale was the lowest (mean index = 2.37) for plants treated with a commercial product based on P. lilacinum, followed by S. feltiae (125 IJs/cm2), X. bovienii (dipping + topical application) and cadaver treatments. The control group had the highest root-knot infection (mean index = 8.55). Total yield from the P. lilacinum-treated plants in the Kepez region was estimated at 18.800 kg/1000 m2, which was the highest yield among all treatments in both regions. S. feltiae and S. feltiae cadaver application treatments followed the P. lilacinum treatment with 17.216 and 16.440 kg/1000 m2 production, respectively. Total yield was 11.184 kg/1000 m2 in the control. The cost analysis of each treatment was calculated based on the total harvested amount of tomatoes per plant x 4000 (the number of tomato plants in a typical 000 m2 greenhouse). The net profit difference between P. lilacinum treated and non-treated (control) greenhouses in Fethiye and Kepez regions was US $ 3268 and 797 US $ for the tomato growers per 1000 m2, respectively.
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•Purpureocillium lilacinum reduced Root-knot nematode galls and increased yield in tomato plants.•Steinernema feltiae infective juvenile and cadaver treatment reduced RKN infection and increased yield.•Mode of application of biocontrol agents significantly affected efficacy.•Economic analysis supports using these biological controls for RKN infection.
The black cutworm (BCW), Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae), is one of the destructive cutworm species. Black cutworm is a highly polyphagous pest that feeds on more than 30 plants, ...many of which are of economic importance such as maize, sugar beet, and potato. The control of BCW larvae relies heavily on the application of synthetic insecticides which have a detrimental impact on human health and the natural environment. In addition, increasing insecticide resistance in many insect species requires a novel and sustainable approach to controlling insect pests. The endosymbionts of entomopathogenic nematodes (EPNs) (Xenorhabdus and Phorohabdus spp.) represent a newly emerging green approach to controlling a wide range of insect pests. In the current study, the oral and contact efficacy of cell suspension (4 × 107 cells ml−1) and cell-free supernatants of different symbiotic bacteria (X. nematophilai, X. bovienii, X. budapestensis, and P. luminescent subsp. kayaii) were evaluated against the mixed groups of 1st-2nd and 3rd-4th instars larvae of BCW under controlled conditions. The oral treatment of the cell suspension and cell-free supernatants resulted in higher mortality rates than contact treatments. In general, larval mortality was higher in the 1st-2nd instar larvae than in the 3rd-4th instar larvae. The highest (75%) mortality was obtained from the cell suspension of X. budapestensis. The results indicated that the oral formulations of the cell suspension and cell-free supernatants of bacterial strains may have a good control potential against the 1st-2nd larvae BCW. However, the efficacy of the cell suspension and cell-free supernatants of tested bacterial strains should be further evaluated under greenhouse and field conditions.
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•The black cutworm (BCW), Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae), considered one of the major polyphagous insect pests.•The chemical control of BCW is quite challenging due to soil-dwelling habits and nocturnal feeding behavior of the larvae.•Xenorhabdus and Photorhabdus bacteria had a great biocontrol efficacy against the 1st/2nd instar larvae larvae of BCW.•The oral formulations of the cell suspension and cell-free supernatants of bacterial strains may have a good control potential against the 1st/2nd larvae BCW.
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