Entomopathogenic nematodes (EPNs) are widely distributed in soils across all continents except Antarctica. Assessing the EPN community structure in an ecoregion can help reveal their biological ...control potential against important crop pests. Common methods for detecting EPNs in soil samples include baiting with sentinel insects, direct observation of extracted nematodes, or use of species-specific primer-probe combinations using qPCR. Less well studied is the use of high throughput sequencing (HTS), which has tremendous potential to characterize soil communities of EPNs and natural enemies of EPNs. Here, for the first time, we compared qPCR and HTS to characterize EPN food webs. The frequency and abundance of 10 EPN species and 13 organisms associated with EPNs from 50 orchard and natural area sites in two ecoregions of Portugal were evaluated using qPCR tools, and results were published in 2019. We applied an HTS approach to analyze frozen DNA samples from 36 sites in that study. Universal primers targeting ITS1 were used for nematode detection. All EPN species detected by qPCR were also detected by HTS. The EPN species and nearly all free-living nematodes detected by both processes were highly correlated (P < 0.01). Steinernema feltiae, the dominant EPN species, was detected by HTS in 55% more sites than by qPCR. HTS also detected more EPN species than did qPCR. Sample accuracy, measured by the fit of Taylor's Power Law to data from each method, was significantly better using HTS (r2 = 0.95, P < 0.01) than qPCR (r2 = 0.76, P < 0.01). The effect of biotic and abiotic variables on individual EPN species did not differ according to ANOVA and multiple regression analyses of both data sets while the drivers of EPN community structure did not differ when analyzing either data set with CCA. Our results combined with decreasing costs of metabarcoding, suggest that HTS may provide the most cost-effective and accurate means of assessing soil food webs of methods currently available.
•First time high-throughput sequencing is used as a detection method for EPN species.•All EPN species detected by qPCR were also detected by HTS approach.•High degree of correlation between HTS and qPCR species relative abundances.•HTS has potential for use in studies of EPN population ecology.•HTS suggests a cost-effective and accurate method assessing soil food webs.
Phlyctinus callosus (Schönherr) (Coleoptera: Curculionidae), or the banded fruit weevil (BFW), causes damage to the fruits, leaves and roots of deciduous fruits and grapevines in the Western Cape ...province. The control of the BFW can be improved by means of combining entomopathogenic fungi (EPF) and entomopathogenic nematodes (EPNs). The combination of commercial isolates of Beauveria bassiana (Bb1), B. bassiana (Bb2), Metarhizium anisopliae (Ma1) and a South African isolate M. anisopliae (MaEA2), with Steinernema yirgalemense against BFW adults and larvae were evaluated in laboratory trials. Four treatment regimens were used where BFW were exposed to the EPF and the EPN separately, and to a combination of EPF and S. yirgalemense either immediately, 1 week or 2 weeks apart. The combined application of the different EPF isolates with S. yirgalemense resulted in higher mortality of BFW in the laboratory. With the application of S. yirgalemense 7 or 14 days after application of Bb2 and Bb1, 100% mortality for both larvae and adults, was obtained. Synergy was noted with Bb1, Bb2, Ma1 and MaEA2 when each was combined with S. yirgalemense, when applied 7 or 14 days after application of the EPF. Interactions showed that the EPF and S. yirgalemense have an additive effect when applied simultaneously, and a synergistic effect was obtained when applied 7 or 14 days after the application of the different EPF. The results indicate that the combination of EPF and an EPN show potential as an economically viable control strategy.
Abstract
Background
Fall armyworm (FAW),
Spodoptera
frugiperda
(J. E. Smith) (Lepidoptera: Noctuidae) is the new invasive pest of different economic crops, threatening the agricultural economy ...worldwide. Chemical insecticides are the main control management strategy applied by almost farmers. As the adverse effect of these chemicals on the environment and human health, improving alternative environmentally friendly control against this pest is urgently needed. In this response, the pathogenicity bioassays of 2 entomopathogenic nematode species (EPNs),
Steinernema
carpocapsae
(All) and
Heterorhabditis
indica
(EGAZ2), on different FAW larval instars (2nd to 6th instars) were assessed under laboratory conditions.
Results
The results cleared that FAW larval mortality rate was varied significantly related to nematode species, post-exposure times and developmental instar stages.
S.
carpocapsae
application was more virulent and effective against all tested instars larvae, registering 100% mortality after 48–72 h post-exposure at different nematode concentrations (150–2400 IJs). However,
H.
indica
caused 100% mortality in early instars only after 96 h, but late instars required a longer time extending to 120–188 h at tested concentrations. In this context, 2nd and 3rd instars were highly susceptible to
Heterorhabditis
species infection. Lower nematode concentrations (150–300 IJs) caused moderate mortality 33.33–50%, respectively, in 5th and 6th full-developed larvae only. All recovery larvae post-infection died in the pupal stage or adult emerged with wing malformation.
Conclusion
The 2 EPN species were virulent against different FAW larval instars at different concentrations and exposure times. Thereby, they are recommended as biocontrol agents against this invasive pest, particularly
S.
carpocapsae
after low-exposure time. This study provides essential information on EPNs, which will further help in the practical application of biological control against fall armyworm.
The emphasis of this review is on the use and potential of entomopathogenic nematodes (EPNs) as biological control agents in sustainable food production across a wide range of agricultural and other ...commodities. To aid with the understanding of the potential of EPNs in sustainable food production, this review also provides overviews on EPN biology and ecology, mass production and application technology, and interactions with other management tools. First discovered in the 1920s, their commercialization as biopesticides in the 1980s was accompanied and followed by an exponential growth in research on their application, biology, and ecology, followed by a further expansion in more basic research areas since the mid-2000s. This review summarizes significant progress made in the research and application of EPN in insect pest management in important food crops including orchards, small fruit, maize, vegetables, tuber crops, greenhouses, and mushrooms. Significant factors affecting the success of EPN commercialization are also discussed. A growing interest in alternatives to synthetic insecticides and in organic agriculture opens opportunities for EPNs, but EPNs will need to be further improved with respect to efficacy, reduced costs, and ease of use. Moreover, their potential to recycle in host populations beckons to be further exploited for long term pest suppression.
Entomopathogenic nematodes (EPNs) from the genera Steinernema and Heterorhabditis are soil-dwelling parasites that feed on insect larvae. They are valuable auxiliaries in the fight against insect ...pests of crops used in market gardening and through the addition of non-native EPNs. However, a better description of the natural distribution of EPNs in agricultural soils will be required to foster their use in crop management programs. The objective of this study was to developan optimal methodology for obtaining an accurate picture of the presence and diversity of EPNs in the maize fields around Pau in South-West France. We combined different approaches for the detection of EPNs in 43 maize plots. We optimized a method for isolating EPNs directly from soil samples based on multiple baiting cycles with Galleria mellonella. With this approach, Steinernema and Heterorhabditis were isolated from 25.5% to 2.5% of the plots, respectively. We also extracted the soil nematofauna. An initial morphological identification of the EPNs present in these samples led to the detection of Steinernema and Heterorhabditis in 2.5 % and 7% of the plots, respectively. We then applied molecular detection techniques to the nematofauna samples, focusing on Steinernema. We detected Steinernema in 16.5% of plots by quantitative realtime PCR (qPCR) and in 35% of plots by digital droplet PCR (ddPCR). We propose a combination of multiple baiting cycles on soil samples with soil nematofauna extraction followed by ddPCR to optimize the detection of EPNs for the analysis of their distribution in agricultural soils.
Entomopathogenic nematodes (EPNs) are widely distributed in soils throughout the world. Their activity as biological control agents is modulated by abiotic and biotic factors (e.g. soil type, ...climatic fluctuation and natural enemies). We sought to identify soil properties in a Mediterranean region, which might be managed to enhance biological control agents’ services provided by EPNs. We hypothesized that responses of EPN soil food web assemblages to abiotic factors in such a Mediterranean region would be consistent with previous observations in other biomes in subtropical and temperate regions, in which pH and variables related to water content were main drivers of such association. We also expected that EPN abundance and species composition would differ between stable botanical habitats (citrus groves, palmetto areas, oaks and pines), with EPNs and associated organisms favoured in cultivated sites (citrus). In spring 2016, 50 georeferenced localities, representing four botanical habitats and two soil-ecoregions (calcareous versus non-calcareous), were surveyed. Using published and de novo real time qPCR tools, we evaluated the frequency and abundance of 10 EPN species and 13 organisms associated with EPNs: 6 nematophagous fungi (NF), 5 free-living nematodes (FLN), and 2 ectoparasitic bacteria. EPN activity was also assessed by traditional insect-baiting, allowing the evaluation of FLN-EPN mixed progeny. EPNs were detected by qPCR in 50% of localities, and strongly correlated with EPN activity. Steinernema feltiae was the dominant EPN species measured by both techniques (qPCR and insect-bait), being widespread in all Algarve, while Heterorhabditis bacteriophora was detected mainly in citrus groves. The species S. arenarium and H. indica were detected by qPCR for the first time in continental Portugal. The molecular analysis of insect cadaver progeny revealed novel FLN-EPN associations with Pristionchus maupasi and P. pacificus. EPN, FLN and NF abundance differed among botanical groups, with citrus groves supporting high numbers of all trophic guilds. Oaks also favoured EPNs. Similarly, calcareous soil-ecoregion supported higher NF, FLN and EPN abundance. Two abiotic variables (pH, and clay content) explained the community variation in multivariate analysis, consistent with key abiotic variables described for other subtropical and temperate regions. The results supported the hypothesis that cultivated perennial habitats favour EPNs and soil organisms that can limit EPN activity as biological control agents.
•Entomopathogenic nematode (EPN) food webs evaluated in Mediterranean Algarve region.•Molecular tools added 2 new EPN species in Portugal to those shown as dominant.•New molecular tools revealed first mixed progeny of Pristionchus-EPN in cadavers.•EPN and associated soil organisms assemblage are driven by vegetation.•Soil pH and clay explained EPN assemblage, as in subtropical and temperate areas.
Display omitted
•EPNs can be applied in infected host cadavers as an alternative to aqueous suspension.•Environmental tolerance of cadaver-produced EPNs was superior to that of aqueous EPNs.•Findings ...have important implications for ecology of EPNs and improved biocontrol.
Environmental factors such as temperature and desiccation impact the survival and efficacy of entomopathogenic nematodes (EPNs). Most studies on environmental tolerance have focused on EPNs applied in aqueous suspension. Another approach for EPN application is via infected host cadavers. Emergence in host cadavers is also more representative of nematodes in natural populations. In prior studies, certain advantages in fitness have been observed with the cadaver application approach relative to aqueous application, yet the impact of environmental stress on these approaches requires investigation. In this study, we compared the effects of various temperatures (heat and cold) and desiccation intervals (48 and 72 hr) on the survival, virulence and reproductive capacity of Heterorhabditis bacteriophora and Steinernema glaseri when applied via cadaver versus aqueous suspension. In the heat tolerance bioassays, following exposure to 30 °C, 35 °C and 37. 5 °C, nematodes (from both species) in the cadaver treatments exhibited higher survival, and reproductive capacity compared with aqueous application. No survival was observed above 37.5 °C regardless of species or application approach. In cold tolerance, no differences were observed between the cadaver and aqueous treatments after a sequence of exposures from 10 °C to −2 °C. In desiccation assays, following exposure to 85% relative humidity for 2 or 3 days, nematodes (from both species) exhibited higher survival and reproduction in the cadaver treatment than in the aqueous treatment, whereas no differences were observed in virulence. This is the first study to find differential stress tolerance among nematodes emerged from infected host cadavers versus those applied in aqueous suspension. Our findings indicate additional advantages when using the cadaver approach for biocontrol applications, and suggest EPNs existing in natural populations may have broader environmental tolerance than those applied via aqueous suspension.
Abstract Background Isolation of novel species of entomopathogenic nematodes (EPNs) with biocontrol potential against important insect pests is very important for the sustainable management of ...economic pests damaging food crops and providing protection to the agricultural environment. This study was aimed to new indigenous EPN isolates from Egyptian agricultural soils and studies its biocontrol potential for further use in the biological control programs. Five out of 15 soil samples obtained from a farm located at the Cairo–Alexandria desert highway was positive for the presence of EPN, using the greater wax moth baiting method. Results Sequencing of the internal transcribed spacer (ITS) region of 4 of the nematode isolates suggested that they belong to the species Heterorhabditis indica. However, one isolate does not show a high similarity to any of the H. indica previously recorded in the database of the Gen Bank and hence was identified as a new Heterorhabditis species and was deposited at the National Center for Biotechnology Information (NCBI) and registered under accession no. (OP555450) under the name of Heterorhabditis alii. This new species was also registered in the ZooBank under the registration link of: LSID urn: lsid: zoobank.org: act: 306F9D57-CC30-4B8E-8B19-4F0E42B08F34. No males were found in this species. Morphological characterization using the light microscope (LM) and scanning electron microscope (SEM) confirmed the identification of this nematode as a new species of the genus Heterorhabditis. Moreover, virulence of this new species against the fall armyworm (FAW), Spodoptera frugiperda (Smith 1797) (Lepidoptera: Noctuidae) was tested in comparison with the foreign EPN species, Heterorhabditis bacteriophora (HP88) and the local Heterorhabditis indica (Mango 2 isolate) and proved to be more effective against this devastative insect pest than the two compared species. Conclusions The present study found out a new species of the EPN genus, Heterorhabditis in Egypt. Our results were confirmed by both morphological and molecular analyses. The efficacy of this new species against the FAW proved to be a potent and safe biocontrol agent that can be used in biological control programs against this invasive insect pest of corn in Egypt and other global countries.
PDF
