Simultaneous exposure of nematophagous fungi, entomopathogenic nematodes and entomopathogenic fungi can modulate belowground insect pest control

Opportunities for optimizing fungal biological control agents for long-term and effective management of insect pests of orchards and vineyards: a review

Novel tactics for controlling insect pests in perennial fruit and nut crops are needed because target pests often display decreased susceptibility to chemical controls due to overreliance on a handful of active ingredients and regulatory issues. As an alternative to chemical controls, entomopathogenic fungi could be utilized as biological control agents to manage insect pest populations. However, development of field ready products is hampered by a lack of basic knowledge. Development of field ready products requires collecting, screening, and characterizing a greater variety of potential entomopathogenic fungal species and strains. Creation of a standardized research framework to study entomopathogenic fungi will aid in identifying the potential mechanisms of biological control activity that fungi could possess, including antibiotic metabolite production; strains and species best suited to survive in different climates and agroecosystems; and optimized combinations of entomopathogenic fungi and novel formulations. This mini review therefore discusses strategies to collect and characterize new entomopathogenic strains, test different potential mechanisms of biocontrol activity, examine ability of different species and strains to tolerate different climates, and lastly how to utilize this information to develop strains into products for growers.

Entomopathogenic pseudomonads can share an insect host with entomopathogenic nematodes and their mutualistic bacteria

A promising strategy to overcome limitations in biological control of insect pests is the combined application of entomopathogenic pseudomonads (EPPs) and nematodes (EPNs) associated with mutualistic bacteria (NABs). Yet, little is known about interspecies interactions such as competition, coexistence, or even cooperation between these entomopathogens when they infect the same insect host. We investigated the dynamics of bacteria-bacteria interactions between the EPP Pseudomonas protegens CHA0 and the NAB Xenorhabdus bovienii SM5 isolated from the EPN Steinernema feltiae RS5. Bacterial populations were assessed over time in experimental systems of increasing complexity. In vitro, SM5 was outcompeted when CHA0 reached a certain cell density, resulting in the collapse of the SM5 population. In contrast, both bacteria were able to coexist upon haemolymph-injection into Galleria mellonella larvae, as found for three further EPP-NAB combinations. Finally, both bacteria were administered by natural infection routes i.e. orally for CHA0 and nematode-vectored for SM5 resulting in the addition of RS5 to the system. This did not alter bacterial coexistence nor did the presence of the EPP affect nematode reproductive success or progeny virulence. CHA0 benefited from RS5, probably by exploiting access routes formed by the nematodes penetrating the larval gut epithelium. Our results indicate that EPPs are able to share an insect host with EPNs and their mutualistic bacteria without major negative effects on the reproduction of any of the three entomopathogens or the fitness of the nematodes. This suggests that their combination is a promising strategy for biological insect pest control.

When Competitors Join Forces: Consortia of Entomopathogenic Microorganisms Increase Killing Speed and Mortality in Leaf- and Root-Feeding Insect Hosts

Combining different biocontrol agents (BCA) is an approach to increase efficacy and reliability of biological control. If several BCA are applied together, they have to be compatible and ideally work together. We studied the interaction of a previously selected BCA consortium of entomopathogenic pseudomonads (Pseudomonas chlororaphis), nematodes (Steinernema feltiae associated with Xenorhabdus bovienii), and fungi (Metarhizium brunneum). We monitored the infection course in a leaf- (Pieris brassicae) and a root-feeding (Diabrotica balteata) pest insect after simultaneous application of the three BCA as well as their interactions inside the larvae in a laboratory setting. The triple combination caused the highest mortality and increased killing speed compared to single applications against both pests. Improved efficacy against P. brassicae was mainly caused by the pseudomonad-nematode combination, whereas the nematode-fungus combination accelerated killing of D. balteata. Co-monitoring of the three BCA and the nematode-associated Xenorhabdus symbionts revealed that the four organisms are able to co-infect the same larva. However, with advancing decay of the cadaver there is increasing competition and cadaver colonization is clearly dominated by the pseudomonads, which are known for their high competitivity in the plant rhizosphere. Altogether, the combination of the three BCA increased killing efficacy against a Coleopteran and a Lepidopteran pest which indicates that this consortium could be applied successfully against a variety of insect pests.

Virulence of the Bio-Control Fungus Purpureocillium lilacinum Against Myzus persicae (Hemiptera: Aphididae) and Spodoptera frugiperda (Lepidoptera: Noctuidae)

Eco-friendly entomopathogenic fungi are widely used to control agricultural insect pests. Purpureocillium lilacinum (Thom.) Luangsa-ard et al. (Hypocreales: Ophiocordycipitaceae) is a nematophagous fungus used for the bio-control of destructive root-knot nematodes. However, its insecticidal activities against agricultural insect pests haven't been widely studied. In this study, P. lilacinum PL-1 was isolated from soil (Hefei, China) and identified by molecular and morphological analyses. The growth rate, spore production, proteinase, and chitinase activities of the isolate were analyzed. Virulence tests against green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae) and fall armyworm (FAW), Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) were performed. The median lethal concentration (LC50) and median lethal time (LT50) against aphids (via immersion) and LT50 against FAW (via injection) were determined. FAW eggs immersed in aqueous conidia suspension were infected after 60 h. Differentially expressed genes (DEGs) in the infection of FAW larvae by P. lilacinum were analyzed by quantitative reverse transcription PCR. The significantly upregulated DEGs include FAW immune genes (antimicrobial peptides, C-type lectins, lysozymes, prophenoloxidase, and peptidoglycan recognition proteins) and fungal pathogenic genes (ligase, chitinase, and hydrophobin). Our data demonstrate that P. lilacinum can be used as an entomopathogenic fungus against agricultural insect pests.

Earthworms and their cutaneous excreta can modify the virulence and reproductive capability of entomopathogenic nematodes and fungi

Earthworms are ecological engineers that can contribute to the displacement of biological control agents such as the entomopathogenic nematodes (EPNs) and fungi (EPF). However, a previous study showed that the presence of cutaneous excreta (CEx) and feeding behavior of the earthworm species Eisenia fetida (Haplotaxida: Lumbricidae) compromise the biocontrol efficacy of certain EPN species by reducing, for example, their reproductive capability. Whether this phenomenon is a general pattern for the interaction of earthworms-entomopathogens is still unknown. We hypothesized that diverse earthworm species might differentially affect EPN and EPF infectivity and reproductive capability. Here we investigated the interaction of different earthworm species (Eisenia fetida, Lumbricus terrestris, and Perionyx excavatus) (Haplotaxida) and EPN species (Steinernema feltiae, S. riojaense, and Heterorhabditis bacteriophora) (Rhabditida) or EPF species (Beauveria bassiana and Metarhizium anisopliae) (Hypocreales), in two independent experiments. First, we evaluated the application of each entomopathogen combined with earthworms or their CEx in autoclaved soil. Hereafter, we studied the impact of the earthworms' CEx on entomopathogens applied at two different concentrations in autoclaved sand. Overall, we found that the effect of earthworms on entomopathogens was species-specific. For example, E. fetida reduced the virulence of S. feltiae, resulted in neutral effects for S. riojaense, and increased H. bacteriophora virulence. However, the earthworm P. excavates increased the virulence of S. feltiae, reduced the activity of H. bacteriophora, at least at specific timings, while S. riojaense remained unaffected. Finally, none of the EPN species were affected by the presence of L. terrestris. Also, the exposure to earthworm CEx resulted in a positive, negative or neutral effect on the virulence and reproduction capability depending on the earthworm-EPN species interaction. Concerning EPF, the impact of earthworms was also differential among species. Thus, E. fetida was detrimental to M. anisopliae and B. bassiana after eight days post-exposure, whereas Lumbricus terrestris resulted only detrimental to B. bassiana. In addition, most of the CEx treatments of both earthworm species decreased B. bassiana virulence and growth. However, the EPF M. anisopliae was unaffected when exposed to L. terrestris CEx, while the exposure to E. fetida CEx produced contrasting results. We conclude that earthworms and their CEx can have positive, deleterious, or neutral impacts on entomopathogens that often coinhabit soils, and that we must consider the species specificity of these interactions for mutual uses in biological control programs. Additional studies are needed to verify these interactions under natural conditions.

Activity of Steinernema colombiense in plant-based oils

Entomopathogenic nematodes (EPNs) are excellent biological control agents. Although traditionally EPN application targeted belowground insects, their aboveground use can be supported if combined with adjuvants. We hypothesized that EPN infective juveniles (IJs) could be combined with plant-based oils as adjuvants, without decreasing their efficacy against insect larvae under various scenarios. Specifically, our objectives were to evaluate the activity of Steinernema colombiense (Nematoda: Steinernematidae) when mixed with two plant-based oils (coconut and olive oils) and maintained at different temperatures and times, or combined with entomopathogenic fungi. First, we evaluated how these oils affected IJ survival and virulence against last instar Galleria mellonella (Lepidoptera: Pyralidae) larvae when maintained at five different temperatures (4, 8, 14, 20, and 24°C) and five incubation times (1, 3, 7, 14, and 21 days), using water as control treatment. Second, we evaluated virulence when combined with these two oils as well as with water (control) and combined with the entomopathogenic fungi (EPF), Beauveria bassiana (Hypocreales: Clavicipitaceae). Infective juvenile survival was higher in coconut than olive oil and water mixtures up to 7 days at 4°C. Conversely, olive oil supported higher larval mortality than coconut oil at 4 to 20°C and 14 days. Similarly, the number of days needed to kill insect larvae increased at extreme temperatures (4 and 24°C) after 14 days. Finally, the EPN + EPF combination showed an additive effect compared to EPN and EPF single treatments. Our findings indicate that our plant-based oil mixtures maintain viable IJs at moderate temperatures and up to 7 to 14 days, and can be used in single EPN mixtures or combined with EPF.

Patterns of Occurrence and Activity of Entomopathogenic Fungi in the Algarve (Portugal) Using Different Isolation Methods

Entomopathogenic fungi (EPF) are distributed in natural and agricultural soils worldwide. To investigate EPF occurrence in different botanical habitats and soil-ecoregions, we surveyed 50 georeferenced localities in the spring of 2016 across the Algarve region (South Portugal). Additionally, we compared three EPF isolation methods: insect baiting in untreated or pre-dried-soil and soil dilution plating on a selective medium. We hypothesized that forest habitats (oak and pine semi-natural areas) and the acidic soil ecoregion may favor EPF occurrence. Overall, EPF species were present in 68% of sites, widely distributed throughout the Algarve. The use of selective media resulted in higher recovery of EPF than did either soil-baiting method. Contrary to our hypothesis, neither vegetation type nor ecoregion appeared to influence EPF occurrence. Traditional and molecular methods confirmed the presence of five EPF species. Beauveria bassiana (34% of sites), was the most frequently detected EPF, using pre-dried soil baiting and soil dilution methods. However, baiting untreated soil recovered Fusarium solani more frequently (26% of sites), demonstrating the utility of using multiple isolation methods. We also found Fusarium oxysporum, Purpureocillium lilacinum and Metarhizium anisopliae in 14%, 8% and 2% of the sites, respectively. Three abiotic variables (pH, soil organic matter and Mg) explained 96% of the variability of the entomopathogen community (EPF and entomopathogenic nematodes) in a canonical correspondence analysis, confirming the congruence of the soil properties that drive the assemblage of both entomopathogens. This study expands the knowledge of EPF distribution in natural and cultivated Mediterranean habitats.

Mortality of Phyllophaga vetula larvae by the separate and combined application of Metarhizium anisopliae, Steinernema carpocapsae and Steinernema glaseri

Phyllophaga spp. are a complex of edaphic insect pests that are present in the corn crops (Zea mays) in México, which are usually controlled with increasing dosages of broad-spectrum chemical insecticides. Several entomopathogenic nematode species can produce acceptable control levels of these larvae. However, the synergistic interaction between fungi and entomopathogenic nematodes (EPN) could improve the control of this insect. This study investigates the mortality of larvae of Phyllophaga vetula by the effect of the separate or combined application of the fungus Metarhizium anisopliae M1cog strain (Ma) and the nematodes Steinernema carpocapsae All strain (Sc) or Steinernema glaseri NJ-43 strain (Sg). In laboratory, dosages of 1 × 106 or 1 × 108 spores/larva and 250 infective juveniles were applied on medium or large size P. vetula larvae contained in vials with sterilized agricultural soil as the assay arena. The separate application of Ma did not kill any larvae, but Sg and Sc killed 40 and 80% of the larvae, respectively. However, the Ma and Sc combination had an important antagonistic interaction that decreased the mortality to 40%, but the combination Ma and Sg had a slight additive interaction that increased the mortality to 47%. The most determining factor in larvae mortality was the nematode used, with Sg as the species with best performance in 6 of the 12 treatments evaluated and with a maximum effectivity of 80% on medium-size larvae if combined with a low dosage of Ma. The combined application of an entomopathogenic fungus and EPN showed no consistent effects on the mortality percentage of P. vetula, mostly because the fungus was not isolated from Phyllophaga larvae.

Scavenging behavior and interspecific competition decrease offspring fitness of the entomopathogenic nematode Steinernema feltiae

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.

Pigment epithelium-derived factor inhibits lung cancer migration and invasion by upregulating exosomal thrombospondin 1

Exosomes are implicated in cancer cell development, migration and invasion. Pigment epithelium-derived factor (PEDF) is a secreted anticancer protein that can regulate lung cancer progression; however, the role of PEDF in non-small cell lung cancer (NSCLC), including metastasis and cancer cell-derived exosome secretion, is unclear. In this study, we analyzed the effects of PEDF on exosome-mediated migration, invasion, and tumorigenicity of cultured NSCLC cells. The results showed that PEDF overexpression significantly reduced NSCLC invasion and migration, while inducing cell aggregation, whereas PEDF knockdown had the opposite effects. Exosomes from NSCLC cells treated with recombinant PEDF had a significantly reduced ability to promote cancer cell motility, migration, and invasion compared to exosomes from untreated cells. Exosomes from PEDF-treated cells contained thrombospondin 1 (THBS1), which inhibited cytoskeletal remodeling and exosome-induced lung cancer cell motility, migration, and invasion. Furthermore, PEDF-overexpressing NSCLC cells formed smaller xenograft tumors with higher THBS1 expression compared to control tumors. Our findings indicate that PEDF decreases the metastatic potential of NSCLC cells through regulation of THBS1 release in cancer cell-derived exosomes, thus uncovering a new mechanism of lung cancer progression.

Enhanced entomopathogenic nematode yield and fitness via addition of pulverized insect powder to solid media

Beneficial nematodes are used as biological control agents. Low-cost mass production of entomopathogenic nematodes (EPNs) is an important prerequisite toward their successful commercialization. EPNs can be grown via in vivo methods or in sold or liquid fermentation. For solid and liquid approaches, media optimization is paramount to maximizing EPN yield and quality. In solid media, the authors investigated the effects of incorporating pulverized insect powder from larvae of three insects (Galleria mellonella, Tenebrio molitor, and Lucillia sericata) at three dose levels (1, 3, and 5%). The impact of insect powder was assessed on infective juvenile (IJ) yield in solid media. Additionally, IJs produced in solid culture were subsequently assessed for virulence, and progeny production in a target insect, Spodoptera litura. The dose level of larval powder had a significant effect on IJ yield in both trials, whereas insect type had significant effect on IJ yield in trial 1 but not in trial 2. The maximum solid culture yield was observed in T. molitor powder at the highest dose in both trials. Moreover, the time-to-death in S. litura was substantially shortened in trial 1 and in trial 2 when IJs from the T. molitor powder treatment were applied. There was no significant effect of combining two insect powders relative to addition of powder from a single insect species. These findings indicate that addition of insect powder to solid media leads to high mass production yields, and the fitness of the IJs produced (e.g., in virulence and reproductive capacity) can be enhanced as well.

Beneficial nematodes are used as biological control agents. Low-cost mass production of entomopathogenic nematodes (EPNs) is an important prerequisite toward their successful commercialization. EPNs can be grown via in vivo methods or in sold or liquid fermentation. For solid and liquid approaches, media optimization is paramount to maximizing EPN yield and quality. In solid media, the authors investigated the effects of incorporating pulverized insect powder from larvae of three insects (Galleria mellonella, Tenebrio molitor, and Lucillia sericata) at three dose levels (1, 3, and 5%). The impact of insect powder was assessed on infective juvenile (IJ) yield in solid media. Additionally, IJs produced in solid culture were subsequently assessed for virulence, and progeny production in a target insect, Spodoptera litura. The dose level of larval powder had a significant effect on IJ yield in both trials, whereas insect type had significant effect on IJ yield in trial 1 but not in trial 2. The maximum solid culture yield was observed in T. molitor powder at the highest dose in both trials. Moreover, the time-to-death in S. litura was substantially shortened in trial 1 and in trial 2 when IJs from the T. molitor powder treatment were applied. There was no significant effect of combining two insect powders relative to addition of powder from a single insect species. These findings indicate that addition of insect powder to solid media leads to high mass production yields, and the fitness of the IJs produced (e.g., in virulence and reproductive capacity) can be enhanced as well.