Steinernema Feltiae Research Articles

Evaluation of Entomopathogenic Nematodes against Red Palm Weevil, Rhynchophorus ferrugineus (Olivier) (Coleoptera: Curculionidae).

Simple SummaryThe red palm weevil is considered the most notorious pest for different species of palms around the globe. Due to the concealed nature of the red palm weevil, the use of biocontrol agents, especially EPNs, is considered most effective. Among biocontrol agents, entomopathogenic nematodes provide effective control of the different developmental stages of the red palm weevil. In the current investigation, the infective capabilities of four different species of entomopathogenic nematodes were investigated against larvae (5th and 6th instars), pupae enclosed in their cocoons, and adult red palm weevil (newly formed), under laboratory and field conditions. Our results indicated that the S. carpocapsae and H. bacteriophora were the most effective EPN species against different developmental stages of the red palm weevil under laboratory as well as field conditions. The larval stage of the red palm weevil was found to be the most susceptible to infection by EPNs compared with pupal and adult stages. From the present findings, we can infer that S. carpocapsae and H. bacteriophora are the most effective EPN strains and recommend their use in the sustainable management of the red palm weevil.Entomopathogenic nematodes play a pivotal role as biocontrol agents for different species of insect pests, including the red palm weevil. In the current investigation, the infective capabilities of four species of entomopathogenic nematodes, including Hetrerorhabditis bacteriophora, Steinernema feltiae, Steinernema glaseri, and Steinernema carpocapsae, were evaluated against larvae, pupae, and adult red palm weevil under laboratory and field conditions. The pathogenic potential of selected nematode species was assessed based on dissection and adult emergence of weevils. Our results indicated that S. carpocapsae and H. bacteriophora, with a respective 94.68 and 92.68% infection rate, were the most effective EPN species against red palm weevil larvae. Focusing on adult emergence, the aforementioned EPNs were comparatively less pathogenic and resulted in 63.60 and 60.20% infested pupae, respectively. It is noted that adult emergence is the better option to evaluate the pathogenic potential of EPNs, compared with the dissection of insects. The S. carpocapsae was found to be most effective against the 6th instar larvae of the red palm weevil and caused 100% mortality at 240 h after treatment. On the other hand, S. glaseri and S. feltiae were found to be the least pathogenic and caused 70 and 76% mortality, respectively. All of the evaluated nematode species were found to be highly infective under field conditions. The S. carpocapsae was found to be the most pathogenic, causing 83.60% mortality of the red palm weevil. However, the tested nematodes were found most effective against larvae, followed by adult weevils, but their effect was minimal against the pupae of red palm weevils. Based on these findings, we conclude that the S. carpocapsae and H. bacteriophora could be used as a sustainable option for the efficient management of the red palm weevil.

Şeftali bahçesinde damla sulama yöntemi ile toprağa uygulanan yerel entomopatojen nematodların kalıcılığının belirlenmesi

The period of persistence of entomopathogenic nematodes (EPNs) in soil is an important factor in the success of biological control efforts. In this study, the persistency of four native Turkish entomopathogenic nematode species, Steinernema feltiae (Filipjev), S. carpocapsae (Weiser), S. affine (Bovien) and Heterorhabditis bacteriophora (Poinar), was investigated in a peach orchard after their application with a drip irrigation system in Çanakkale Province, Turkiye, in 2018 and 2019. The EPNs were applied at the rate of 50 IJs/cm2. After application, the persistency of the EPNs was determined with soil sampling on a monthly basis. EPN persistence in the soil was 90 days and 150 days in 2018 and 2019, respectively. Additionally, the persistency of the EPNs in soil after their application varied, depending on environmental factors. The longer survival of EPNs in soil after application is important for the increase of the efficiency of EPNs against pests. It was concluded that the local EPN species have potential for use in the biological control of agricultural pests.

Efficacy of single and combined applications of entomopathogenic fungi and nematodes against the pupae of colorado potato beetle (Leptinotarsa decemlineata [Say]), (Coleoptera: Chrysomelidae)

BackgroundThe lethal effects of different entomopathogenic fungi (EPF) and nematodes (EPN) on the pupae of the Colorado Potato Beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae) were investigated in a two-step study when used separately or together. In the first step, Nostalgist (Beauveria bassiana strain Bb-1, Agrobest Co.), Steinernema feltiae (Filipjev) (Rhabditida: Steinernematidae), Heterorhabditis bacteriophora Poinar, 1976 (Rhabditida: Heterorhabditidae) (Bioglobal Co.), 2 Turkish isolates of Beauveria bassiana BIM-001 and BY2 were applied separately to the pupal stage of pest in the soil. In the experiments, 3 different concentrations (150, 200, and 250 million infective juveniles (IJs)/100 l water) of EPN and a single concentration (1x108 spores/ml for and maximum recommended field dose 1 × 108 CFU/ml) of EPF were used. In the second step, BIM-001 and BY2 isolates of B. bassiana were combined with both EPN species; S. feltiae + B. bassiana BIM-001, S. feltiae + B. bassiana BY2, H. bacteriophora + B. bassiana BIM-001, H. bacteriophora +B. bassiana BY2 were applied to pupae. At this stage, 150 million IJs/100 l water which was the maximum recommended field concentration for EPN and 1 × 108 spores/ml for local EPF isolates were used.ResultsAccording to the study results, pupae deaths were significantly higher in Nostalgist (74%) than those of B. bassiana BIM-001, B. bassiana BY2, S. feltiae, and H. bacteriophora (P<0.05). While both EPN caused higher mortality than B. bassiana BY2, B. bassiana BIM-001 had the highest mortality rates. The combination of S. feltiae + B. bassiana BIM-001 at the highest mortality rate (80%) was found statistically different and significant from other EPF + EPN treatments on pupae. Moreover, there were non-statistical differences between the other EPF and EPN combinations.ConclusionIt was found that the combined use of EPF and EPN was more effective on the pupae of L. decemlineata than a single application. According to the results of the study, it may be promising to use EPN and EPF together for the control of the Colorado Potato Beetle pupae.

Potential biological control agents of Zeugodacus cucurbitae (Coquillett): A review

AbstractZeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae) is a serious agro‐economic pest of cucurbits around the world. Management of tephritid fruit flies is till date mainly dependent on the use of chemical pesticides. In a rising concern about environment quality and rapid development of resistance in insect pests, biological control of insect pests is being contemplated, and in response, research approaches are constantly evolving. Various naturally occurring control agents of melon fruit fly such as parasitoids, bacteria, fungi and nematodes have potential in the management of Z. cucurbitae. Many parasitoids including Psyttalia fletcheri, Fopius arisanus, Dirhinus giffardii and Spalangia endius are known to attack various life stages of Z. cucurbitae. Although parasitoids are being principally exploited for control of Z. cucurbitae, various other entomopathogens such as fungi (Beauveria bassiana, Paecilomyces fumosoroseus, Metarhizium anisopliae), bacteria (Bacillus thuringiensis), nematodes (Heterorhabditis indica, Steinernema feltiae) and microbial toxins/products (spinosad, avermectin) are being investigated or used for biological control. The development of farming methodologies with greater credence on ecosystem services such as biological control of Z. cucurbitae will increase sustainability of agroecosystems. This review provides a concise compilation of these biological control agents along with their effectiveness and will help researchers in designing various integrated pest management strategies against Z. cucurbitae that involve biological control agents.

Mortality of the oriental fruit fly, Bactrocera dorsalis, during pupation in insect pest suppressive soils

The oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), is an important pest of various crops. Little is known about the role naturally present soil‐entomopathogens play in its mortality. Preimaginal mortality of B. dorsalis during pupation in soil was determined in 3‐dl plastic pots in the laboratory, simulating natural conditions. Eleven treatments included standard potting soil, sterilized sand, no pupation medium, standard soil amended one‐by‐one with beneficial soil organisms [the fungi Beauveria bassiana (Bals.‐Criv.) Vuill., Metarhizium robertsii JF Bisch, SA Rehner &amp; Humber, Isaria fumosorosea Wize, and Glomus spp. (each one dose), and the nematode Steinernema feltiae (Filipjev) (three doses)], and standard soil amended with a consortium of beneficals. Preimaginal mortality varied widely from 32–36% (Glomus spp., untreated soil, and S. feltiae low dose) to 85% (no pupation medium). From all treatments with beneficials, amending standard potting soil with a high dose of S. feltiae caused the highest mortality (80%). A microbial consortium led to much higher mortality (77.5%) than any of its single components alone: S. feltiae medium dose (58%), B. bassiana (56%), and M. robertsii (50%). The two other microbial treatments (I. fumosorosea and Glomus spp.) did not significantly increase mortality compared to untreated soil during pupation. We conclude that mortality during pupation of B. dorsalis under field conditions is likely to be highly important to the population dynamics of the pest. Therefore, management of the soil in agricultural fields, including orchards, to favour microbial antagonists of insects can be a powerful tool in the management of this important pest.

Efficacy of authentic bio-nematicides against the root-knot nematode, Meloidogyne javanica infecting tomato under greenhouse conditions

The root-knot nematode (RKN), Meloidogyne javanica is considered one of the most widely distributed and economically damaging plant-parasitic nematodes worldwide. Given the exacerbation of the environmental pollution problem with chemical nematicides, the use of biological nematicides is one of the most acceptable alternative methods in nematode management by the farming community. Four bio-nematicides namely: NT (Steinernema feltiae), MM (Ascophyllum nodosum and Bacillus amyloliquefaciens), GA sol+ (A. nodosum, B. amyloliquefaciens, and Trichoderma harzianum), and Ortie-Prele (aqueous extract of nettle and horsetail (Equisetum arvense)) were evaluated for their efficacy against M. javanica infecting tomato plants under greenhouse conditions. Their efficiencies were compared to a positive control and NemGuard Granules (garlic granule extract) as a standard nematicide. Treatment effects on the growth parameters were also examined. All tested treatments gave high nematicidal effect, except for the Ortie-Prele. The highest reductions in root galling (63%), as well as the number of egg masses (98%), eggs (96%), second-stage juveniles (J2s) (93%), and the reproduction factor (RF = 2.36) were obtained by the NT treatment, which was superior to the efficacy of the standard nematicide 52.63%, 91.58%, 88.30%, and 92.07%, respectively. The Ortie-Prele treatment gave the lowest reduction for the previous nematode criteria 0%, 53.96%, 12.39%, and 11.84%, respectively. On the other hand, all treatments, significantly improved tomato growth parameters; plant length, shoot fresh weight and, root systems when compared to the standard nematicide (Nemguard Granules), and the positive control. The highest increase in shoot length (30.90%), root length (58.13%) and shoot weight (30.98%) were obtained by GA sol+, while Ortie-Prele recorded the highest increase in root weight systems (91.89%). Therefore, our results indicated that NT, MM, and GA sol + proved to be crucial components for an integrated management of M. javanica in tomato crops.

VIRULENCE OF ENTOMOPATHOGENIC NEMATODES TO THREE SOFT SCALE INSECT SPECIES

Virulence of commercial strains of entomopathogenic nematode (EPN) Steinernema carpocapsae (Weiser), Steinernema feltiae Filipjev and Heterorhabditis bacteriophora Poinar (Rhabditida: Steinernematidae, Heterorhabditidae), were tested on young females of Pulvinaria hydrangeae Steinweden, Partenolecanium corni (Bouché) and Coccus pseudomagnoliarum (Kuwana) (Hemiptera, Coccidae) and a native strain of H. bacteriophora was tested on citricola scale, C. pseudomagnoliarum. The laboratory tests were carried out in small plastic Petri dishes with infective juveniles (IJ) applied on filter paper covering the bottom. Results showed that all EPN tested were virulent to all three soft scale insect species. Recorded mortality of insects at the highest concentration of approximately 50 IJ per cm2 exceeded 64% in all combinations of nematode and scale species tested. Within the same nematode concentration, scales’ mortality of 90% and above was recorded for P. corni with all nematode species, P. hydrangeae with S. carpocapsae (Nemastar) and C. pseudomagnoliarum with native H. bacteriophora strain. All scale species were good hosts for all nematode species. This is the first report of EPNs to parasitize soft scale insects and one of the few among Coccoidea. The level of parasitism recorded is promising for potential use in management of scale insects.

Exploring the Use of Entomopathogenic Nematodes and the Natural Products Derived from Their Symbiotic Bacteria to Control the Grapevine Moth, Lobesia botrana (Lepidoptera: Tortricidae).

Simple SummaryThe European grapevine moth (EGVM) Lobesia botrana (Lepidoptera: Tortricidae) attacks vineyards in Europe, the Middle East, and North and South America. Global movement toward sustainable agriculture urges the development of environmentally friendly tools that can replace traditional pesticides. Entomopathogenic nematodes (EPNs) are well-known biological control agents against various arthropod pests. The EPNs act together with symbiotic bacteria that produce natural products with insecticidal potential. Novel formulations and application technology allow their application against aerial pests, including those associated with vineyards. This study investigated the viability of four EPN species and their corresponding bacteria derivates (unfiltered ferment, UF, or cell-free supernatant, CFS) against EGVM (larval and pupa instars). The results revealed that all EPN species killed various EGVM larval stages. Killing pupae required a higher number of IJs than controlling larvae. Steinernema carpocapsae registered the most promising results, killing ~50% L1 and >75% L3/L5 in 2 days. The use of the bacterial bioactive compounds achieved similar results, with UF registering higher activity than CFS. Overall, we demonstrated that both EPN and bacterial bioproducts have a great potential to control EGVM in sustainable viticulture. Further research in co-formulation with adjuvants is required to ensure their survival in the aboveground grapevine areas. The European grapevine moth (EGVM) Lobesia botrana (Lepidoptera: Tortricidae) is a relevant pest in the Palearctic region vineyards and is present in the Americas. Their management using biological control agents and environmentally friendly biotechnical tools would reduce intensive pesticide use. The entomopathogenic nematodes (EPNs) in the families Steinernematidae and Heterorhabditidae are well-known virulent agents against arthropod pests thanks to symbiotic bacteria in the genera Xenorhabdus and Photorhabdus (respectively) that produce natural products with insecticidal potential. Novel technological advances allow field applications of EPNs and those bioactive compounds as powerful bio-tools against aerial insect pests. This study aimed to determine the viability of four EPN species (Steinernema feltiae, S. carpocapsae, S. riojaense, and Heterorhabditis bacteriophora) as biological control agents against EGVM larval instars (L1, L3, and L5) and pupae. Additionally, the bioactive compounds from their four symbiotic bacteria (Xenorhabdus bovienii, X. nematophila, X. kozodoii, and Photorhabdus laumondii subsp. laumondii, respectively) were tested as unfiltered ferment (UF) and cell-free supernatant (CFS) against the EGVM larval instars L1 and L3. All of the EPN species showed the capability of killing EGVM during the larval and pupal stages, particularly S. carpocapsae (mortalities of ~50% for L1 and >75% for L3 and L5 in only two days), followed by efficacy by S. feltiae. Similarly, the bacterial bioactive compounds produced higher larval mortality at three days against L1 (>90%) than L3 (~50%), making the application of UF more virulent than the application of CFS. Our findings indicate that both steinernematid species and their symbiotic bacterial bioactive compounds could be considered for a novel agro-technological approach to control L. botrana in vineyards. Further research into co-formulation with adjuvants is required to expand their viability when implemented for aboveground grapevine application.

Potent Ant Deterrents Emitted from Nematode-Infected Insect Cadavers

Most known species of entomopathogenic nematodes (EPNs) are generalist obligate parasites of insects. They kill their hosts within days after infection and mortality is mainly caused by toxins produced by bacteria that co-infect the hosts and serve as food for the nematodes. EPNs can infect a very broad spectrum of insects and these insects can therefore be expected to have evolved strategies to avoid infection. Indeed, ants are known to avoid feeding on EPN-infected insect cadavers, most likely because they are repelled by semiochemicals that emanate from the cadavers. The source and nature of these repellents are so far unknown. In a series of behavioral and chemical analytical experiments we identified hexadecanal and 2-heptadecanone as two compounds that are emitted by insect larva that are infected by the EPN Steinernema feltiae, but not by uninfected larvae. When spiking honey water with the two semiochemicals, they were confirmed to be highly deterrent to the ant Lasius niger. The environmentally benign hexadecanal and 2-heptadecanone could be employed to ward off ants and possibly other pests. Additional experiments are needed to fully determine their application potential.

Population Dynamics and Control Potential of the Soil-Dwelling Stages of the South African Citrus Thrips, Scirtothrips aurantii (Thysanoptera: Thripidae), on Avocado

Scirtothrips aurantii (Thysanoptera: Thripidae) is a recently confirmed economic pest of avocado (Persea americana). Damage by S. aurantii, through their feeding on avocado fruit results in corky tissue development (scarring), making the fruit unsuitable for export. The study aimed to monitor S. aurantii population dynamics during the critical early fruiting period by means of dispersal/emergence (D/E) traps and fruit infestation indices. The field efficacy of biologicals (Beauveria bassiana, Steinernema feltiae), the pyrethroid beta-cyfluthrin, and the semi-synthetic spinosyn, spinetoram, against soil-dwelling stages of S. aurantii during early fruit development were determined. Finally, the study aimed to establish the pupation sites of S. aurantii in avocado. Above ground, population dynamics fluctuated directly in response to the host plant's phenological changes and were modified by rainfall. Control of soil-dwelling stages by the insecticides and the effectiveness of D/E traps in monitoring S. aurantii populations were not demonstrated, probably because the populations trapped using the D/E traps were not representative of the above-ground populations, as evidenced by fruit infestation indices. Under laboratory conditions, 81.60 % of mature larvae pupated away from the soil, demonstrating that S. aurantii does not passively drop to the ground in an avocado orchard, but actively seeks out dark, sheltered areas to pupate.

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.

Entomopathogenic nematodes for control of carrot weevil: efficacy and longevity in muck and mineral soils.

Carrot weevil is an important pest throughout carrot-producing regions in Canada. Pesticides to control carrot weevil adults require application when the majority of adults have emerged and often this occurs after oviposition has already commenced and damage will be realized. One alternative to conventional pesticides are entomopathogenic nematodes. We studied four commercially available entomopathogenic nematode products (Steinernema feltiae, S. carpocapsae, S. kraussei and Heterorhabditis bacteriophora) for efficacy against carrot weevil in Nova Scotia and Ontario carrot fields in 2017 and 2018. The longevity and infectivity of the products in fine sandy loam soil (Ontario) and sandy loam soil (Nova Scotia) were evaluated using Galleria mellonella larvae. In Nova Scotia soils, only S. kraussei when applied twice, showed some efficacy to reduce damage from carrot weevil in 2017. In Ontario, an early application of H. bacteriophora and S. feltiae significantly reduced the percentage of carrots with weevil damage in 2018. Longevity and infectivity of S. carpocapsae and S. feltiae (against G. mellonella) was obtained up to 6 weeks post application in Nova Scotia in 2017. Similarly, S. feltiae showed infectivity up to 9 weeks post application in Ontario and Nova Scotia in 2018. Entomopathogenic products showed an ability to survive and remain infective for up to 9 weeks in soils without irrigation. Timing of application to effect control of carrot weevil requires further study. The influence of soil moisture on the longevity and infectivity of these products is discussed. © 2021 Her Majesty the Queen in Right of Canada International Pest Management Science © 2021 Society of Chemical Industry. Reproduced with the permission of the Minister of Agriculture and Agri-Food Canada.

Laboratory virulence of entomopathogenic nematodes to the sweetpotato whitefly, Bemisia tabaci.

The sweetpotato whitefly, Bemisia tabaci Middle East-Asia Minor 1 (MEAM1), is a major insect pest on vegetable crops worldwide. Enormous economic losses result from direct and indirect plant damage caused by MEAM1. Biological control using entomopathogenic nematodes (EPN) may be an effective alternative strategy against MEAM1 because this pest has developed resistance to most insecticides. First, nine EPN species (Heterorhabditis bacteriophora, H. indica, H. georgiana, H. floridensis, Steinernema feltiae, S. carpocapsae, S. riobrave, S. glaseri, and S. rarum) were investigated for virulence to MEAM1 third instar nymphs on snap bean leaves under laboratory conditions. The mortality of MEAM1 nymphs was evaluated at 3 days post-inoculation (dpi). Compared to the water control, the application of the nine EPN species except S. glaseri resulted in significantly higher mortality of MEAM1 nymphs, such as H. bacteriophora (66.31%), H. floridensis (56.38%), S. carpocapsae (54.54%), and S. rarum (57.80%). Subsequently, the four virulent EPN species, H. bacteriophora, H. floridensis, S. carpocapsae, and S. rarum were evaluated further for virulence to MEAM1 nymphs on snap bean and tomato leaves. The mortality of MEAM1 nymphs was assessed at 3 dpi and 7 dpi. There were no significant differences in MEAM1 nymphal mortality between tomato and snap bean at either 3 dpi or 7 dpi. The mortality of MEAM1 nymphs caused by the application of H. floridensis (99.25%) was significantly higher than the other three EPN species and the water control at 7dpi. The results indicate that H. floridensis is a very promising biocontrol agent for B. tabaci management.

Infected host responses across entomopathogenic nematode phylogeny.

We used a phylogenetic framework to examine the relationship between entomopathogenic nematode (EPN) vertical dispersal and infectivity when EPNs are exposed to a mixture of compounds found in late-stage EPN-infected insect cadavers. EPNs from five phylogenetically close and distant species (Heterorhabditis bacteriophora, H. georgiana, H. megidis, H. indica and Steinernema feltiae) were exposed to cadaver macerate produced by their own species’ infection and by H. bacteriophora infected hosts. We found that only three of the five species (H. bacteriophora, H. indica and S. feltiae) responded to exposure to their own macerate by increasing rates of dispersal. When we exposed all five species to a H. bacteriophora infected host macerate, we found that only H. bacteriophora responded by increasing dispersal, and that the most distantly related species (S. feltiae) essentially halted dispersal. These findings suggest that (1) responses to cadaver macerate vary, and (2) there may be a relationship between inherent dispersal rates and sensitivity to macerate exposure, as the most rapidly dispersing species (H. megidis) showed no response to macerate exposure.

Intraspecific virulence of entomopathogenic nematodes against the pests Frankliniella occidentalis (Thysanoptera: Thripidae) and Tuta absoluta (Lepidoptera: Gelechiidae).

Entomopathogenic nematodes (EPN) are excellent biocontrol agents against various insect pests. Novel biotechnological approaches can enhance their utility against insects above-ground, opening a new venue for selecting superior EPN against certain insects. We hypothesize that different populations of the same species but from different origins (habitat, ecoregion) will differ in their virulence. This study aimed to evaluate the virulence of various EPN populations against two pests of worldwide incidence and damage to high value crops: Frankliniella occidentalis (Thysanoptera: Thripidae) and Tuta absoluta (Lepidoptera: Gelechiidae). We tested 10 EPN populations belonging to three EPN species: Heterorhabditis bacteriophora (Koppert, MG-618b, AM-203, RM-102), Steinernema feltiae (Koppert, RS-5, AM-25, RM-107), and Steinernema carpocapsae (Koppert, MG-596a). Each EPN population was tested at two concentrations. Frankliniella occidentalis was tested at 160 and 80 IJs/cm2 and T. absoluta at 21 and 4 IJs/cm2. Control treatments followed the same experimental procedure but only adding distilled water. Overall, whenever different, higher IJs concentration resulted in lower adult emergence, higher larval mortality, and shorter time to kill the insects. Considering the low concentration, S. feltiae provided the best results for both insects and instars investigated, while H. bacteriophora and S. carpocapsae required a high concentration to reach similar or slightly better results. Differences among populations of each of the species were detected, but only the native populations of H. bacteriophora populations showed consistently higher control values against both insects/instar compared with the commercial one. Differences among S. feltiae and S. carpocapsae populations depended on the IJs concentration, insect, and instar. We consider S. feltiae a very promising species for their application against F. occidentalis and T. absoluta, with the Koppert population as the most consistent among the populations tested. Specific EPN-populations of S. carpocapsae and H. bacteriophora were good candidates against certain instar/insects at high concentrations. This study emphasized the importance of intraspecific variability for EPN virulence.

Volatile organic compounds of Metarhizium brunneum influence the efficacy of entomopathogenic nematodes in insect control

The entomopathogenic fungus (EPF) Metarhizium brunneum occupies the same ecological niche as entomopathogenic nematodes (EPN), with both competing for insects as a food source in the rhizosphere. Interactions between these biocontrol agents can be antagonistic or synergistic. To better understand these interactions, this study focussed on investigating the effect of M. brunneum volatile organic compounds (VOCs), 1-octen-3-ol and 3-octanone, on EPN survival and behaviour. These VOCs proved to be highly toxic to the infective juveniles (IJs) of the EPN Steinernema carpocapsae, Steinernema feltiae and Heterorhabditis bacteriophora with mortality being dose dependent. Chemotaxis studies of H. bacteriophora IJs in Pluronic F127 gel revealed significant preference for the VOCs compared with controls for all tested concentrations. The VOCs also impacted on the test insects in a dose-dependent manner with 3-octanone being more toxic to Galleria mellonella, Cydia splendana and Curculio elephas larvae than 1-octen-3-ol. Mortality of C. splendana and G. mellonella larvae was significantly higher when exposed to relatively high doses (>25%) of 3-octanone. Lower doses of 3-octanone and 1-octen-3-ol immobilised test insects, which recovered after exposure to fresh air for 2 hrs. In depth studies on H. bacteriophora showed that exposure of IJs to > 10% concentration of 3-octanone or 1-octen-3-ol negatively affected infectivity whereas exposure to lower doses (0.1%, 0.01%) had no effect. The VOCs affected IJs, reducing penetration efficacy and the number of generations inside G. mellonella but they failed to inhibit the bacterial symbiont, Photorhabdus kayaii. The ecological significance of VOCs and how they could influence EPF-EPN insect interactions is discussed.

Dissemination of Isaria fumosorosea Spores by Steinernema feltiae and Heterorhabditis bacteriophora.

Entomopathogenic nematodes and fungi are globally distributed soil organisms that are frequently used as bioagents in biological control and integrated pest management. Many studies have demonstrated that the combination of biocontrol agents can increase their efficacy against target hosts. In our study, we focused on another potential benefit of the synergy of two species of nematodes, Steinernema feltiae and Heterorhabditis bacteriophora, and the fungus Isaria fumosorosea. According to our hypothesis, these nematodes may be able to disseminate this fungus into the environment. To test this hypothesis, we studied fungal dispersal by the nematodes in different arenas, including potato dextrose agar (PDA) plates, sand heaps, sand barriers, and glass tubes filled with soil. The results of our study showed, for the first time, that the spreading of both conidia and blastospores of I. fumosorosea is significantly enhanced by the presence of entomopathogenic nematodes, but the efficacy of dissemination is negatively influenced by the heterogeneity of the testing arena. We also found that H. bacteriophora spread fungi more effectively than S. feltiae. This phenomenon could be explained by the differences in the presence and persistence of second-stage cuticles or by different foraging behavior. Finally, we observed that blastospores are disseminated more effectively than conidia, which might be due to the different adherence of these spores (conidia are hydrophobic, while blastospores are hydrophilic). The obtained results showed that entomopathogenic nematodes (EPNs) can enhance the efficiency of fungal dispersal.

Response of grey slug to entomopathogenic nematodes

ABSTRACT Biological control using entomopathogenic nematodes (EPNs) is known as an ecofriendly strategy in integrated pest management. The terrestrial slug Parmacella ibera is a major pest of vegetables and citrus trees in north of Iran. The heavy costs and environmental concerns of synthetic molluscicides led the study to use EPNs, against the slug P. ibera. The present study was arranged to evaluate and compare the performance of EPNs, Steinernema feltiae, S. carpocapsae and Heterorhabditis bacteriophora on P. ibera population (mortality rate) and the feeding rate in vitro, and also its damage (seedlings establishment rate) in vitro. Phasmarhabditis hermaphrodita, as a slug parasite nematode, and also the metaldehyde, as a molluscicide, were used as positive controls. The results of the study showed that the highest mortality rate (%) and the seedlings establishment rate (%) of the slug population were observed in S. carpocapsae, S. feltiae and H. bacteriophora treatments, respectively. The feeding rate (%) of the slug declined in the treatments with H. bacteriophora, S. feltiae and S. carpocapsae, respectively. The mortality rate of the pest was enhanced by extending the exposure time and increasing levels of the nematodes. Therefore, it can be concluded that the EPNs S. carpocapsae, S. feltiae and H. bacteriophora are able to control the slug P. ibera population.

Impact of entomopathogenic nematodes on Africanized honey bees Apis mellifera L. (Hymenoptera: Apidae) workers

Africanized honey bee populations (Apis mellifera L.) have been decreasing mainly due to the intense use of synthetic insecticides associated with pollution and climate change. To minimize these impacts on the environment and bee populations, the use of biological control agents has been intensified. These products are generally safer for non-target insects, such as bees, which are important pollinating insects. Thus, the objective of this study was to evaluate the impact of entomopathogenic nematodes on the longevity of the Africanized honey bee A. mellifera workers. Seven treatments were used: Heterorhabditis amazonensis, Heterorhabditis bacteriophora, Heterorhabditis indica, Steinernema carpocapsae, Steinernema feltiae, and Steinernema rarum, at a concentration of 40 infective juveniles per cm2 (IJs/cm²), and a control in which autoclaved distilled water was used. Two bioassays were performed: 1) spraying nematodes on the workers and 2) spraying nematodes on glass plates, in which the bees remained for two hours. Each treatment consisted of five replicates with 20 bees each. Bees were kept in cages of PVC (20 × 10 cm) covered with a voile fabric and provided pieces of cotton soaked in water and Candy paste. The cages were kept in a climatized room (27 ± 2 °C temperature, 60 ± 10% relative humidity, and 12 h photophase) and the mortality was evaluated from 12 to 240 hours. In bioassay 1, the three treatments with nematodes of the genus Steinernema reduced the longevity of the workers (103.9, 96.3, and 99.6 h) when compared to treatments with Heterorhabditis (149.7, 126.8, and 134.7 h), of which, only H. amazonensis (149.7 h) did not differ from the control (166.0 h). In bioassay 2, all treatments reduced the longevity of honey bees (155.4 to 93.9 h) in relation to the control (176.1 h). Entomopathogenic nematodes, especially Heterorhabditis, need to be tested using other methodologies and for different durations of exposure and application because in the laboratory, they were less selective to A. mellifera.

Tolerance of the mealworm beetle, Tenebrio molitor, to an entomopathogenic nematode, Steinernema feltiae, at two infection foci, the intestine and the hemocoel

An entomopathogenic nematode, Steinernema feltiae K1, exhibits pathogenicity in various insect hosts, however, its virulence among the target insect species varies. Specifically, a coleopteran insect, Tenebrio molitor, is less susceptible to S. feltiae than are lepidopteran insects. We analyzed the low virulence of S. feltiae against T. molitor sequentially, in entering the gut lumen and penetrating the hemocoel, and in hemocoelic immune defenses by comparing the responses to those of a lepidopteran insect, Spodoptera exigua. Infective juveniles (IJs) of S. feltiae exhibited higher virulence and produced more progeny IJs in S. exigua than in T. molitor. The difference in IJ behavior was observed in the IJ invasion rate (IJs in gut lumen/IJs treated) after treatment, in which a lower rate was observed in T. molitor (20.4%) than in S. exigua (55.5%). Also, a lower hemocoelic penetration rate of IJs (IJs in hemocoel/IJs in gut) was observed in T. molitor (54%) than in S. exigua (74%) 24 h after feeding treatment. To investigate the immune defense in the hemocoel, insect hemolymph samples were incubated with IJs. The encapsulation behavior and phenoloxidase activity was higher in T. molitor hemolymph than in S. exigua hemolymph, which resulted in a significantly higher nematicidal activity in S. exigua. The humoral immune responses against S. feltiae were also different between the two species. The expression of two antimicrobial peptides, cecropin and attacin 1, was much higher in T. molitor. Furthermore, eicosanoid biosynthetic activity against S. feltiae was different in the two host species; sPLA2 activity was highly inducible in T. molitor but not in S. exigua. These results suggest that variability of the immune defense in the target insects, as well as in the invasion and penetration rates of IJs to the hemocoel, plays a crucial role in determining the insecticidal virulence of S. feltiae.