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•Pheromone treated EPNs exhibited enhanced dispersal in soil columns.•Pecan weevils, and black soldier flies had lowest survival with pheromone treated EPNs.•Pheromones increase EPN ...dispersal and host mortality.
Inconsistency in entomopathogenic nematode (EPN) efficacy is still one of the biggest challenges for the wider adoption of EPNs as biocontrol agents. Previous studies demonstrated that extracts from EPN-infected hosts enhance dispersal and efficacy, two key factors in success of EPNs. Some active components in the insect host cadavers responsible for dispersal, ascarosides, have been identified as nematode pheromones. We hypothesized that pheromone extracts increase dispersal of EPN infective juveniles (IJs) leading to increased efficacy. First, we determined whether pheromone extracts improved IJ movement/dispersal in soil columns baited with Tenebrio molitor larvae. We found that pheromone extracts induced higher numbers of Steinernema carpocapsae and Steinernema feltiae IJs to move towards T. molitor larvae in the bottom of the column compared to IJs treated with infected cadaver macerate and water, positive and negative controls, respectively. Furthermore, the number of S. carpocapsae IJs that invaded T. molitor larvae was higher for the pheromone extract treatment than the controls. S. feltiae IJs that were pretreated with pheromone extracts and macerate (positive control) infected T. molitor at the same rate but invasion was superior to IJs that were treated with water. Consistent with the soil column tests, both S. carpocapsae and S. feltiae IJs treated with pheromone extracts performed better in killing larvae of two economically important insect larvae, pecan weevil, Curculio caryae, and black soldier fly, Hermetia illucens, in greenhouse tests compared to IJs treated with water. We demonstrated pheromone-mediated behavioral manipulation of a biological control agent to enhance pest control potential. Conceivably, nematodes can be exposed to efficacy-enhancing pheromones prior to field application.
Commercial-scale field studies were conducted in citrus orchards to test the efficacy of entomopathogenic nematodes (EPNs) in controlling the soil-dwelling life stages of the key pest, Thaumatotibia ...leucotreta. Trials were conducted in three provinces of South Africa from 2011 to 2013. Two EPN species were tested: Heterorhabditis bacteriophora and Steinernema feltiae. Both EPN species were applied underneath citrus tree canopies, either with a spray machine or through the microsprinkler irrigation system. The concentration of nematodes and frequency of application varied. Efficacy of these treatments was measured by evaluation of EPN infection of sentinel T. leucotreta larvae in the soil at various intervals after application and by T. leucotreta infestation of fruit. Successful control was recorded in several trials, with EPN infection of larvae frequently reaching 80 %. However, in a few trials, this level of infection was assisted by naturally occurring EPNs. Fruit infestation by T. leucotreta larvae was reduced by up to 88 %. Efficacy appeared to be limited by suboptimal soil moisture and temperature. The former was influenced mainly by mode and relative thoroughness of irrigation before and after EPN application. This was best obtained through microsprinkler application. Nematode species and concentration also influenced efficacy. Both EPN species survived and persisted in the soil of the treated orchards for up to 4 months. Promising results support their potential for use in an integrated pest management programme in citrus in South Africa.
•Thaumatotibia leucotreta is an important pest of citrus in sub-Saharan Africa.•Heterorhabditis bacteriophora and Steinernema feltiae are virulent to T. leucotreta.•In field trials, more than 80 % of T. leucotreta larvae were infected with nematodes.•Fruit infestation with T. leucotreta larvae was reduced by up to 88 %.•Best results were achieved with monthly applications of EPNs for four months.
Entomopathogenic nematodes (EPNs) are widely used as a biological control agent in pest management. The purpose of this study was to determine the effectiveness and penetration rates of certain EPNs. ...Three different EPN species were utilized in the study: Heterorhabditis bacteriophora HBH hybrid strain, Steinernema carpocapsae TUR-S4 isolate, Steinernema feltiae TUR-S3 and S-Bilecik isolates. These isolates were applied at different doses (50, 100, 150, 200, 250, 300, 350, and 400 Infective Juveniles (IJs)/Petri) on larvae of Tenebrio molitor and adults of Rhyzopertha dominica. Additionally, the penetration rates of the mentioned EPN species on T. molitor larvae and R. dominica adults were determined. As a result, the highest mortality rate observed in R. dominica adults was 93.33% when treated with the HBH isolate at the dose of 400 IJs/Petri dishes. For T. molitor larvae, the highest mortality rate was 100% at doses of 8.85 IJs/cm2, 10.60 IJs/cm2, 12.40 IJs/cm2, 14.15 IJs/cm2 for HBH and TUR-S3, 10.60 IJs/cm2, 12.40 IJs/cm2, 14.15 IJs/cm2 for TUR-S4, and 7.10 IJs/cm2, 8.85 IJs/cm2, 10.60 IJs/cm2, 12.40 IJs/cm2, 14.15 IJs/cm2 for S-Bilecik. When examining the penetration rates, the highest rate of 23.33% was observed in R. dominica adults treated with HBH, while for T. molitor, this rate was 22.67% in individuals treated with HBH. These findings underscore the importance of continued investigation into the potential of these EPNs for sustainable pest management strategies.
•Entomopathogenic nematodes (EPNs) play a crucial role as biological control agents in controlling agricultural pests.•The HBH isolate of Heterorhabditis bacteriophora showed high mortality rates of 93.33% in Rhyzopertha dominica adults.•Specific doses for each EPN species resulted in a 100% mortality rate for Tenebrio molitor larvae.•The HBH isolate demonstrated the highest penetration rates, with 23.33% observed in R. dominica and 22.67% in T. molitor.
The fall webworm (FWW), Hyphantria cunea Drury (Lepidoptera: Erebidae), is an invasive and polyphagous insect pest of many economically important crops such as hazelnuts, apple, and mulberry. ...Recently, there have been an increasing number of reports about the damaging activities of FWW from hazelnut growing areas of Turkey indicating that currently existing control methods fail to satisfy the expectations of growers. Entomopathogenic nematodes (EPNs) in the Steinernematidae and Heterorhabditidae (Nematoda: Rhabditida) families and the symbiotic bacteria they carry in their intestine have a great potential for the management of many agriculturally important pests. In this study, the symbiotic bacteria of local EPN species (Heterorhabditis bacteriophora AVB-15, Steinernema feltiae KCS-4S, and Steinernema bicornotum MGZ-4S) recovered from the central Anatolia region was characterized using recA gene region as Photorhabdus luminescens, Xenorhabdus bovienii and Xenorhabdus budapestensis. The contact (25, 50, 100, 200 IJs/Petri) and oral efficacies of the infective juveniles (IJs) (25, 50, 100, 200 IJs/leaf) of these EPN isolates determined on 3rd/4th instar larvae, and cell-free supernatants from the identified symbiotic bacteria were evaluated separately on the 3rd and 4th larval instars of FWW in Petri dish environment under laboratory conditions (25 ± 1 °C, 60% of RH). In the Petri dish bioassays of EPN species, the most pathogenic isolate at the 1st DAT and 4th DAT was S. feltiae which caused 50% mortality at the highest concentration (200 IJs/Petri) and the highest mortality rate (97.5%) were achieved at 4th DAT by H. bacteriophora AVB-15 isolate. Surprisingly, the mortality rates were generally higher at the lowest concentrations and 82.5% mortality were reached 4th DAT by S. bicornotum at the lowest concentration (25 IJs/leaf) in the leaf bioassays. Mortality rates were higher in both Petri dish and filter paper efficacies of cell-free supernatants at the 2nd DAT and the highest mortality (87.5%) was reached in the contact efficacy studies when applied X. bovienii KCS-4S strain. The results suggest that the tested EPN species and CFSs have good potential for biological control of the larvae of FWW and can contribute to the IPM programs of FWW. However, the efficacy of both IJs of EPNs and CFSs of their symbiotic bacteria on larvae of FWW requires further studies to verify their efficiency in the field.
•The fall webworm (FWW) is considered one of the invasive pests of many plants.•The chemical control is the most preferred method by farmers in severe infestations of FWW.•We tested the efficacy of entomopathogenic nematodes (EPNs) and their bacterial cell-free superatants (CFSs) against the larvae of FWW.•Foliar applications of EPNs and their CFSs could play an important role in the management of larvae of Hyphantria cunea.
•Two novel behaviorally active compounds for EPN IJs were revealed.•The two species tested (Steinernema feltiae and S. carpocapsae) responded differently to the behaviorally active compounds.•Within ...the blend of volatiles emitted by EPN-infected insect cadavers, 1-nonene plays a behavior-active role.•Ethanol is a novel attractant for S. feltiae IJs.•The differences in the responses to the compounds support known data on scavenging trends of the EPNs tested.
Entomopathogenic nematodes (EPNs) parasitize insects in the soil and are applied as environmentally friendly means for pest control in agriculture. Knowledge of how EPN infective juveniles (IJs) find their prey can be used to increase their effectiveness. Chemical signals in the soil are undoubtedly important but exactly which ones is little known. We hypothesized that volatile compounds emitted by EPN-infected larval cadavers could act as such signals. The objective of the study was to test the behavioral effects of 1-nonene which is known as a volatile compound emitted by several EPN-infected insect cadavers. Behavioral tests revealed that 1-nonene was attractive to IJs of both Steinernema feltiae and S. carpocapsae. High concentrations of the compound were repellent to S. feltiae and attractive to S. carpocapsae IJs. Low concentrations were attractive to S. feltiae (those from 104 to 106 times lower than the repellent concentrations) but did not affect the behavior of S. carpocapsae. Ethanol (solvent used for control tests) was attractive to S. feltiae IJs and not to those of S. carpocapsae. Both compounds are new agents involved in the behavior control of these EPN species. Different responses of IJs of two taxonomically closely related EPN species to chemical compounds could indicate interspecific difference in foraging. Behavioral reactions of S. carpocapsae IJs are more in line with the strategy of the scavenger.
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•Steinernema feltiae but not Heterorhabditis bacteriophora reproduced in insect cadavers.•Progeny rates and F1 pathogenicity were lower in scavenging S. feltiae.•High scavenging ...pressure by Oscheius onirici reduced F1 S. feltiae fitness.•Entomopathogenic nematodes (EPNs) compromised fitness of saprophytic organisms.•EPNs as scavengers were not compromised by the presence of saprophytic organisms.
Entomopathogenic nematodes (EPNs) are well-studied biocontrol agents of soil-dwelling arthropod pests. The insecticidal efficiency of EPNs is modulated by food web dynamics. EPNs can reproduce in freeze-killed insect larvae, even in competition with free-living bacterivorous nematodes (FLBNs) in the genus Oscheius. The objective of this study was to assess the efficiency of EPNs as scavengers when competing with free-living saprophagous nematodes and fungi, and to determine the possible impact on subsequent EPN offspring fitness. Live and freeze-killed larvae of Galleria mellonella were used to evaluate the reproduction rate and progeny fitness of two EPN species, Heterorhabditis bacteriophora and Steinernema feltiae, applied individually or combined with the FLBN species Oscheius onirici or Pristionchus maupasi, or Aspergillus flavus, an opportunistic saprophytic fungus. We hypothesized that (1) EPN scavenging behaviors previously observed (for H. megidis and S. kraussei) apply to other EPN species, (2) infective juveniles (IJs) emerging from freeze-killed larvae will display reduced pathogenicity and reproduction, and (3) fitness reduction will be amplified by exposure to other organisms competing for the resources. The reproduction rate of S. feltiae was lower in freeze-killed larvae than in larvae infected and killed by the nematode, whereas H. bacteriophora failed to reproduce as a scavenger. The S. feltiae F1 IJs that emerged from freeze-killed larvae exhibited lower pathogenicity rates than IJs resulting from entomopathogenic activity, and also lower reproductive rates if they experienced high FLBN competitive pressure during development. This study illustrates that scavenging is a suboptimal alternative pathway for EPNs, especially in the face of scavenger competition, even though it provides a means for some EPN species to complete their life-cycle.
•Allium sativum EO increased EPN mortality and reduced their infective capacity.•Satureja montana EO caused low mortality rates but exhibited repellency towards EPNs.•Mentha suaveolens EO minimally ...affected EPNs survival, infectivity and reproduction.•M. suaveolens EO is suggested as the most compatible oil for field use with EPNs.•Field validation is essential to confirm the practical applicability of these findings.
The European truffle beetle, Leiodes cinnamomeus, is the most important pest in black truffle (Tuber melanosporum) plantations. Entomopathogenic nematodes (EPNs) are promising biological control agents against L. cinnamomeus. Essential oils (EOs) are also recently being investigated for the control of the adults of this pest. Therefore, both control methods could be combined in Integrated Pest Management (IPM) programs to enhance their efficacy. However, limited information exists regarding the effects of the EOs on EPNs and so their compatibility. The aims of our work were to study the effects of three previously described insecticidal and nematicidal essential oils, Allium sativum, Mentha suaveolens, and Satureja montana, on the survival, infectivity, reproduction, and attraction behaviour of three EPN species: Steinernema feltiae, Steinernema carpocapsae and Heterorhabditis bacteriophora. Therefore, we conducted three experiments under laboratory conditions to observe the lethal and sublethal effects by direct contact, the lethal effect by fumigation, and the chemotaxis response. Allium sativum caused the highest mortality rates in all three EPN species at 24 and 72 h post application whether by direct contact (97–99%) or fumigation (40–42%), and it also reduced their infective capacity on Galleria mellonella. Satureja montana EO caused low mortality rates compared to A. sativum, but it was significantly more lethal (6–8%) than the control (0–3%) at 72 h in the direct contact assay. It also displayed repellent properties against S. feltiae and H. bacteriohora in the chemotaxis assay. In contrast, M. suaveolens EO exhibited minimal impact on the survival, infectivity and reproduction of all three EPN species. Therefore, our results suggest M. suaveolens oil may be the most compatible EO for use integrated with EPNs. Further validation under field conditions and in the presence of L. cinnamomeus is necessary to confirm the practical applicability of these findings.
The entomopathogenic nematode (EPN)
Steinernema feltiae
, which carries the symbiotic bacterium
Xenorhabdus bovienii
in its gut, is an important biocontrol agent. This EPN could produce a suite of ...complex metabolites and toxin proteins and lead to the death of host insects within 24–48 h. However, few studies have been performed on the key biomarkers released by EPNs to kill host insects. The objective of this study was to examine what substances produced by EPNs cause the death of host insects. We found that all densities of nematode suspensions exhibited insecticidal activities after hemocoelic injection into
Galleria mellonella
larvae. EPN infection 9 h later led to immunosuppression by activating insect esterase activity, but eventually, the host insect darkened and died. Before insect immunity was activated, we applied a high-resolution mass spectrometry-based metabolomics approach to determine the hemolymph of the wax moth
G. mellonella
infected by EPNs. The results indicated that the tryptophan (Trp) pathway of
G. mellonella
was significantly activated, and the contents of kynurenine (Kyn) and 3-hydroxyanthranilic acid (3-HAA) were markedly increased. Additionally, 3-HAA was highly toxic to
G. mellonella
and resulted in corrected mortalities of 62.50%. Tryptophan metabolites produced by EPNs are a potential marker to kill insects, opening up a novel line of inquiry into exploring the infestation mechanism of EPNs.
•Entompathogenic nematodes improve the transmission of Cordyceps fumosorosea spores.•Steinernema feltiae and S. carpocapsae were found to spread spores most effectively.•Nematode’s 2nd stage cuticle ...is an important factor for spore dispersal.•Adhesive medium increased spore distribution in the soil environment.
Entomopathogenic nematodes and fungi are organisms that cause epizootics in insect and are therefore important bioagents. Many studies focus on the effectiveness of either entomopathogenic nematodes or fungi for controlling pests, though it has been shown that a combination of the two entomopathogens may enhance their efficacy against host and the nematodes can disseminate fungal spores on cuticle. We focused on evaluating the effects of foraging behaviour of Steinernema feltiae, Heterorhabditis bacteriophora, and Steinernema carpocapsae on the dissemination of Cordyceps fumosorosea. Additionally, we investigated how the nematode’s 2nd stage cuticle as well as various adhesives impact spore transmission.
Fungal dispersal via nematodes was studied through two experimental designs: soil-filled glass tubes and soil columns. The latter experiment also used alginate and sunflower oil as adhesives to explore ways to enhance spore dispersal.
Results illustrated that nematodes improve the transmission of C. fumosorosea spores; particularly conidia. The nematodes S. feltiae and S. carpocapsae were found to spread spores most effectively, depending however on the experimental soil conditions. Research revealed that the nematode’s 2nd stage cuticle is an important factor for spore dispersal; without it, transmission rates drop significantly. Sunflower oil was determined to be the most successful adhesive medium and increased spore distribution for all tested nematodes.
These findings indicate the potential use of adhesives in biocontrol to enhance nematode dissemination of EPF spores. Additional research regarding adhesives, as well as the mechanisms of spore adhesion to the nematode may be of importance in the future.
Entomopathogenic nematodes (EPN) are well-established plant protection tools for the control of insect pests. The release of EPN species is often limited to species that are endemic in the country. ...Therefore, surveys to check for the presence of EPN species in the country are necessary. Here, a sampling and baiting method based on the in situ attraction of EPN to insects contained in a plastic tube is described. Heterorhabditis downesi was isolated from overgrown dunes at the Baltic coast and Steinernema feltiae from chromic luvisol further inland. This is the first report of the presence of H. downesi in Germany.
