Biocontrol potential of the entomopathogenic nematodes Heterorhabditis bacteriophora and Steinernema carpocapsae on cucurbit fly,Dacus ciliatus (Diptera: Tephritidae)

Entomopathogenic nematodes (EPNs) from the families Steinernematidae and Hererorhabditidae are considered excellent biological control agents against many insects that damage the roots of crops. In a regional survey, native EPNs were isolated, and laboratory and greenhouse experiments were conducted to determine the infectivity of EPNs against the cucurbit fly, Dacus ciliatus Loew (Diptera: Tephritidae). Preliminary experiments showed high virulence by a native strain of Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae) and a commercial strain of Steinernema carpocapsae Weiser (Rhabditida: Steinernematidae). These two strains were employed for further analysis while another native species, Steinernema feltiae, was excluded due to low virulence. In laboratory experiments, larvae and adult flies were susceptible to nematode infection, but both nematode species induced low mortality on pupae. S. carpocapsae had a significantly lower LC₅₀ value against larvae than H. bacteriophora in filter paper assays. Both species of EPNs were effective against adult flies but S. carpocapsae caused higher adult mortality. When EPN species were applied to naturally infested fruit (150 and 300 IJs/cm²), the mortality rates of D. ciliatus larvae were 28% for S. carpocapsae and 12% for H. bacteriophora. Both EPN strains successfully reproduced and emerged from larvae of D. ciliates. In a greenhouse experiment, H. bacteriophora and S. carpocapsae had similar effects on fly larvae. Higher rates of larval mortality were observed in sandy loam and sand soils than in clay loam. The efficacy of S. carpocapsae and H. bacteriophora was higher at 25 and 30°C than at 19°C. The results indicated that S. carpocapsae had the best potential as a biocontrol agent of D. ciliatus, based on its higher virulence and better ability to locate the fly larvae within infected fruits.     

Susceptibility of Queensland fruit fly,Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), to entomopathogenic nematodes

Queensland fruit fly, Bactrocera tryoni (Froggatt), is the economically most significant Australian tephritid pest species with a large invasion potential, yet relatively little work on its biological control has been undertaken. Entomopathogenic nematodes (EPNs) are of potential interest for control of this fruit fly species as it pupates in the soil. Specifically, the pre-pupal stage of B. tryoni may present a unique window for EPN application, as fully developed larvae drop from infested fruit to the soil for pupation. For the first time, we tested the capacity of three EPN species with different foraging strategies, Steinernema feltiae, Steinernema carpocapsae and Heterorhabditis bacteriophora, to cause larval and pupal mortality in B. tryoni across a range of EPN concentrations (50, 100, 200, 500 and 1000 infective juveniles IJs cm^-2), substrate moisture (10, 15, 20 and 25% w/v) and temperatures (15, 20, 25 and 30 °C). We found that all EPN species tested caused environment and density dependent mortality in the third larval instar while pupae were not affected. Steinernema feltiae caused high mortality across different IJ concentrations and over a wider moisture and temperature range than the other two EPN species. High mortality caused by S. carpocapsae and H. bacteriophora was more limited to high IJ concentrations and a narrower moisture and temperature range. Our findings highlight the potential of EPNs for the control of B. tryoni and warrant further laboratory and field experiments to evaluate their efficacy under the wide environmental conditions that B. tryoni can occur in.     

Laboratory and semi-field evaluation of three entomopathogenic nematode species on two non-target insect predators,Coccinella septumpunctata (Coleoptera: Coccinellidae) and Chrysoperla carnea (Neuroptera: Chrysopidae)

Abstract

Biocontrol potential of the entomopathogenic nematodes (EPNs) on the second-instar larvae of the non-target insect predators, Coccinella septumpunctata and Chrysoperla carnea as compared to Spodoptera littoralis (Boisd.) was evaluated. The pathogenicity of EPNs, namely, Heterorhabditis bacteriophora, Steinernema feltiae and Steinernema carpocapsae at concentrations 100, 200, 400, 800 and 1600 IJs/cup) were tested at 2, 4 and 6 days’ post-inoculation. Laboratory results showed significant differences among the mortality rates of different tested larvae, for each concentration at different time intervals. H. bacteriophora induced the highest mortality followed by S. carpocapsae treatment. However, S. feltiae was found to be more safety on predators as it causes less mortality at 6 days of treatment. The values of half lethal concentrations (LC₅₀) were 614.06, 3797.43 and 676.47 IJs/cup for C. Carnea and 390.60, 1209.88 and 503.65 IJs/cup for C. septumpunctata treated by H. bacteriophora, S. feltiae and S. carpocapsae, respectively. In semi-field experiments, there were non-significant differences among mortality of each predator indicated at concentrations of the different EPNs after 2 days or 6 days’ post-inoculation. The study revealed a lethal pathogenic effect of EPNs against insect pests but caused low mortality on the non-target ones.     

Efficacy of entomopathogenic nematodes against potato tuber moth,Phthorimaea operculella (Lepidoptera: Gelechiidae) under laboratory conditions

The susceptibility of potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) to native and commercial strains of entomopathogenic nematodes (EPNs) was studied under laboratory conditions. Native strains of EPNs were collected from northeastern Iran and characterised as Steinernema feltiae and Heterorhabditis bacteriophora (FUM 7) using classic methods as well as analysis of internal transcribed spacer (ITS) and D2/D3 sequences of 28S genes. Plate assays were performed to evaluate the efficiency of five EPN strains belonging to four species including Steinernema carpocapsae (commercial strain), S. feltiae, Steinernem glaseri and H. bacteriophora (FUM 7 and commercial strains). This initial assessment with 0, 75, 150, 250, 375 and 500 IJs/ml concentrations showed that S. carpocapsae and H. bacteriophora caused the highest mortality in both larval and prepupal stages of P. operculella, PTM. Thereafter, these three strains (i.e. S. carpocapsae, H. bacteriophora FUM 7 and the commercial strains) were selected for complementary assays to determine the effects of soil type (loamy, loamy–sandy and sandy) on the virulence of EPNs against the second (L2) and fourth instar (L4) larvae as well as prepupa. A soil column assay was conducted using 500 and 2000 IJs in 2-ml distilled water. Mortality in the L2 larvae was not affected by the EPN strain or soil type, while there was a significant interactive effect of nematode strains and soil type on larval mortality. The results also showed that EPN strains have higher efficiency in lighter soils and caused higher mortality on early larvae than that in loamy soil. In L4 larvae, mortality of PTM was significantly influenced by nematode strain and applied concentrations of infective juveniles. The larval mortality induced by S. carpocapsae was higher than those caused either by a commercial or the FUM 7 strain of H. bacteriophora. Prepupa were the most susceptible stage.     

Virulence of entomopathogenic nematodes to larvae of the guava weevil, Conotrachelus psidii (Coleoptera: Curculionidae), in laboratory and greenhouse experiments

The guava weevil, Conotrachelus psidii, is a major pest of guava in Brazil and causes severe reduction in fruit quality. This weevil is difficult to control with insecticides because adults emerge over a long period, and larvae develop to the fourth-instar inside the fruit and move to the soil for pupation. We assessed the virulence of entomopathogenic nematodes to fourth-instar larvae in soil by comparing their susceptibility to nine species or strains: Heterorhabditis bacteriophora HP88, H. baujardi LPP7, and LPP1, H. indica Hom1, Steinernema carpocapsae All and Mexican, S. feltiae SN, S. glaseri NC, and S. riobrave 355. In petri dish assays with sterile sand at a concentration of 100 infective juveniles (IJs) of a given nematode species/strain, larval mortality ranged from 33.5 to 84.5%, with the heterorhabditids being the most virulent. In sand column assays with H. baujardi LPP7, H. indica Hom1, or S. riobrave 355 at concentrations of 100, 200, and 500 IJs, mortality was greater than the control only for H. baujardi (62.7%) and H. indica (68.3%) at the highest concentration. For H. baujardi LPP7 in a petri dish assay, the time required to kill 50 and 90% of the larvae (LT₅₀ and LT₉₀) for 100 IJs was 6.3 and 9.9 days, whereas the lethal concentration required to kill 50 and 90% of the larvae (LC₅₀ and LC₉₀) over 7 days was 52 and 122.2 IJs. In a greenhouse study with guava trees in 20-L pots, 10 weevil larvae per pot, and concentrations of 500, 1000 or 2000 IJs, H. baujardi LPP7 caused 30 and 58% mortality at the two highest concentrations. These results show that H. baujardi is virulent to fourth-instar larvae and has potential as a biological control agent in IPM programs.     

Efficacy of commercial formulations of entomopathogenic nematodes against tropical sod webworm,Herpetogramma phaeopteralis (Lepidoptera: Crambidae)

Large quantities of insecticides are used on warm season turfgrasses to combat pest infestations. To investigate the potential for microbial control, we screened commercially available entomopathogenic nematode products against Herpetogramma phaeopteralis Guenée, an economically injurious pest in the south‐eastern United States and Caribbean islands. All tested products, based on Steinernema carpocapsae, S. feltiae, Heterorhabditis bacteriophora, H. megidis and H. indica, were pathogenic to H. phaeopteralis larvae in the laboratory, but S. carpocapsae caused the highest mortality. Amongst nematode species, median lethal concentration (LC₅₀) was not different for three different larval sizes (based on 95% CL) with the exception of H. indica, which had higher LC₅₀ for small larvae. The number of infective juvenile stages (IJs) produced per White trap was significantly greater from larvae infected by H. bacteriophora and least for those infected by H. indica. A proprietary formulation of S. carpocapsae ‘Millenium^®’ was chosen for further greenhouse experiments. Overall, the neonicotinoid insecticide clothianidin provided the best control, but greenhouse experiments also revealed that the label rate of Millenium (10⁶ IJ/l at 2500 l/ha) reduced webworm populations by 83–93% and was as effective as clothianidin against larger‐size larvae. Our data suggest that commercial formulations of S. carpocapsae can be a good option for H. phaeopteralis biocontrol, but further field studies are warranted to confirm effectiveness under different environmental scenarios.     

Efficacy of two entomopathogenic nematodes Heterorhabditis bacteriophora and Steinernema carpocapsae for control of the leopard moth borer Zeuzera pyrina (Lepidoptera: Cossidae) larvae under laboratory conditions

The biological traits of the entomopathogenic nematodes (EPNs), Steinernema carpocapsae and Heterorhabditis bacteriophora, against the larvae of the leopard moth, Zeuzera pyrina were evaluated in the laboratory. The traits included pathogenicity, penetration potential as well as foraging behaviour. Plate assays were performed using a range of EPN concentrations (5, 10, 20, 50 and 100 infective juveniles (IJs) per larva). The LC₅₀ values for S. carpocapsae and H. bacteriophora were 6.4 and 8.4 IJs larva^?1 after 72 h. Both EPN species caused high mortality in branch experiments. Significantly higher mortality rates occurred in the larger larvae after exposure to S. carpocapsae. Both EPN species successfully penetrated the Z. pyrina larvae as well as larvae of Galleria mellonella L. (Lepidoptera: Galleridae).The proportional response of H. bacteriophora to host-associated cues was strongly higher than S. carpocapsae in Petri dishes containing agar 1, 12 and 24 h after EPN application. These results highlight the efficiency of EPNs for the control of Z. pyrina larvae. However, due to the cryptic habitat of Z. pyrina larvae in their galleries in the trees, field trails need to be conducted to further evaluate this potential.     

Compatibility between Forficula auricularia and entomopathogenic nematodes to be used in pome fruit pest management

Use of predators, parasitoids and entomopathogens as biocontrol agents in pome fruit production can lead to more efficient and sustainable pest management programmes. The European earwig (Forficula auricularia Linnaeus [Dermaptera: Forficulidae]) is a major predator of key pests in pome fruit orchards, and entomopathogenic nematodes (EPNs) of the families Steinernematidae and Heterorhabditidae are obligate parasites of a large number of insect species. Therefore, the interaction between earwigs and EPNs can play an important role in pest management programmes. Susceptibility of the European earwig to Steinernema carpocapsae, Steinernema feltiae (Steinernematidae) and Heterorhabditis bacteriophora (Heterorhabditidae) was evaluated. S. carpocapsae was the only tested EPN capable of killing the European earwig. However, the European earwig can detect the presence of S. carpocapsae and therefore avoid nematode‐treated shelters. An earwig deterrent activity in EPN‐killed codling moth larvae that reduces the foraging of European earwig on insect cadavers containing nematodes and allows nematodes to complete their life cycle was also assessed with the three species of nematodes. These findings suggest a positive compatibility between the European earwig and EPNs.     

Interactions between entomopathogenic nematodes and imidacloprid for rose sawfly control

Rose sawfly, Arge ochropus (Gmelin), is one of the most important pests of ornamental plants such as roses and wild rose bushes in Northern Iran. We investigated the interactions between the insecticides imidacloprid and the entomopathogenic nematodes Heterorhabditis bacteriophora and Steinernema carpocapsae as control agents of fifth-instar larvae in the laboratory. The larvae were very susceptible to S. carpocapsae (LC₅₀: 21 infective juvenile per larva) and H. bacteriophora (LC₅₀: 32). Combinations of two imidacloprid rates (LC₃₀ and LC₅₀) and four rates of each nematode species (LC₂₅–LC₇₅) were tested. Combinations with the lower imidacloprid rate except for that with the highest H. bacteriophora rate caused higher mortality than both respective single-agent treatments. In combination with the higher imidacloprid rate, only one combination with H. bacteriophora and two combinations with S. carpocapsae caused higher mortality than both respective single-agent treatments. Interactions were generally stronger at the lower imidacloprid rate and were stronger for S. carpocapsae (synergistic in seven combinations, additive in one) than for H. bacteriophora (synergistic in two, additive in six). Synergistic imidacloprid-S. carpocapsae combinations could be a useful tool for the control of A. ochropus larvae that would simultaneously control other common pests susceptible to imidacloprid.     

Improving foliar applications of entomopathogenic nematodes by selecting adjuvants and spray nozzles

This study explores the influence of a selection of adjuvants and of three different nozzle sizes on the foliar application of entomopathogenic nematodes (EPNs). Two EPN species were studied: Steinernema feltiae and Steinernema carpocapsae. A viability test of EPNs suspended in different solutions of adjuvants showed that all selected alcohol ethoxylates and an alkyl polysaccharide have an immobilising effect on the selected nematode species. In a sedimentation test, xanthan gum proved to be the only adjuvant in a broad selection, capable of delaying sedimentation of EPNs in suspension. Without xanthan gum, sedimentation of S. carpocapsae and S. feltiae was noticeable after 20 and 10 minutes, respectively. When xanthan gum (0.3 g/L) was added to the suspension, no signs of sedimentation were noticed after 20 minutes with both EPN species. An ISO 02 flat fan nozzle can clog when spraying S. carpocapsae. A deposition test determined that an ISO 04 standard flat fan nozzle provides a higher relative deposition on cauliflower leaves and is therefore a better nozzle choice than the bigger ISO 08 standard flat fan nozzle for spraying S. carpocapsae. The addition of a spreading agent improved the deposition of S. carpocapsae. Adding xanthan gum to the EPN-spreading agent mixtures did not further improve deposition.     

The potential use of entomopathogenic nematodesagainst Typhaea stercorea

Four entomopathogenic nematode species, Steinernema carpocapsae, S. feltiae, Heterorhabditis bacteriophoraand H. megidis, were tested in a petri dish assay against larvae and adults of the hairy fungus beetle Typhaea stercorea. In general, adults were less susceptible than larvae and the LC₅₀ decreased with the duration of the exposure to nematodes. S. carpocapsae was the most effective species against adult beetles (LC₅₀ after 96 hours exposure =67 nematodes/adult). Against larvae S.carpocapsae and H. megidis were comparablyeffective with an LC₅₀ of 30 and 55nematodes/larvae, respectively. S. carpocapsaewas tested at 70 and 100% RH against adults in baits of either chicken feed or crushed wheat, both supplemented with horticultural capillary matting pieces in order to obtain a wet weight of 50–60%. At70% RH no significant effect of the nematodes was obtained due to desiccation of the bait. In chickenfeed at 100% RH the mortality reached 80% with 500nematodes/adult. In wheat significant mortality was obtained only at 5000 nematodes/adult. Heavy growth of mould probably limited the nematode infection. When the bait was used in tube traps, desiccation and growth of mould was prevented, but nematode efficacy dropped to 4.4% in the traps and 12% in the surrounding litter. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evaluation of the virulence of entomopathogenic nematodes as a biological control agents against Gryllotalpa gryllotalpa (Gryllotalpidae)

The European mole cricket Gryllotalpa gryllotalpa Linnaeus (Orthoptera: Gryllotalpidae) is a key pest of several crops in different regions of the world. The mole crickets usually damage seedlings, feeding aboveground on foliage or stem tissue and belowground on roots and tubers. In biological control, entomopathogenic nematodes (EPNs) are used against many insect pests inhabiting the soil as safe alternatives to chemical pesticides. The present study aimed to evaluate the virulence of the EPNs Heterorhabditis bacteriophora strain (HP88) and Steinernema carpocapsae strain (All) against the adults of European mole cricket G. gryllotalpa under laboratory and field conditions. Three concentrations of each of the EPNs H. bacteriophora and S. carpocapsae were tested against G. gryllotalpa. Infected adults of the pest with nematodes, at the concentration of 2000/cup, attained a mortality rate of (96%), when treated with S. carpocapsae and (72%) when treated with H. bacteriophora 8 days post-treatments. Mortality percentage of G. gryllotalpa adults increased as the concentration of the nematodes increased. Adults' mortality of G. gryllotalpa reached 100% when treated with the combination of the 2 nematode's strains at all concentrations 4 days post-treatments. At the 3 tested concentrations, 500, 1,000 and 2,000 IJs/adults, H. bacteriophora showed a higher reproductive rate in vivo than S. carpocapsae. A single adult of G. gryllotalpa treated with H. bacteriophora produced the average of 29,972, 74,768 and 140,474 IJs/adult, at the 3 concentrations, respectively. Under field application, a combination of EPNs successfully reduced the loss of the cabbage seedlings and the population's number of the mole crickets after 3 applications in the 2 seasons of (2019 and 2020). Therefore, EPNs as biological control agents can be recommended against the mole cricket G. gryllotalpa in vegetable crops as s pest management practice in an integrated pest management programme.     

Infectivity of entomopathogenic nematode Steinernema carpocapsae Pocheon strain (Nematoda: Steinernematidae) on the green peach aphid Myzus persicae (Hemiptera: Aphididae) and its parasitoids

Infectivity of entomopathogenic nematode (EPN) Steinernema carpocapsae Pocheon strain on the green peach aphid Myzus persicae and its parasitic wasps (e.g., Aphidius colemani, Aphidius gifuensis and Diaeretiella rapae) was evaluated under laboratory conditions. Infective juveniles (IJs) of S. carpocapsae Pocheon strain had low infectivity against nymph and adult stages of M. persicae, showing 2% and 6.7% of mortality, respectively. Application of the EPNs had little effect on mummies caused by the three parasitoid species, allowing them to remain intact. No IJ invaded the host, regardless of EPN application rate. The parasitoid emergence from mummies ranged from 80% to 85% in the presence of EPN while 79–86% was recorded in the absence of EPN. However, the presence of the IJs reduced oviposition by the three parasitoid species, decreasing the rate up to 59% when the nematodes were applied before parasitoid release, while little difference in oviposition was observed when nematodes were applied after parasitoid release.     

Efficacy and persistence of entomopathogenic nematodes for black cutworm control in turfgrass

Field experiments were conducted in turf maintained under golf course fairway conditions in May, June, and August 2009 and in August and September 2010 to evaluate the ability of entomopathogenic nematodes to control larval populations of the black cutworm, Agrotis ipsilon, on golf courses. Commercial products containing the entomopathogenic nematodes Heterorhabditis bacteriophora, Steinernema carpocapsae, S. feltiae, and S. riobrave were applied at 1.0 or 2.5×10⁹ infective juveniles per ha against fourth-instar black cutworms. Larval mortality and turf damage were evaluated at 4 and/or 7 days after treatment (DAT). Steinernema carpocapsae was the best performing species due to a combination of high control rates (average 83%), most consistent results (70–90% range), high speed of kill (average 68% at 4 DAT), and prevention of significant turf damage despite very high larval densities at 0 DAT. Efficacy of S. feltiae and H. bacteriophora was often similar to that of S. carpocapsae but overall less consistent. Short-term persistence of the nematodes was evaluated in four turfgrass sites maintained under golf course putting green, fairway, or rough conditions in June and August 2009 by baiting soil samples at 0, 4, 7, and 14 DAT. Relative to recovery immediately after application, at least 50% of S. feltiae and 25% of S. carpocapsae consistently persisted up to 4 days in one of the greens and up to 7 days in some trials. Our finding suggests that S. carpocapsae and S. feltiae may provide adequate black cutworm control in golf course turf under moderate summer temperatures.     

Virulence of entomopathogenic nematodes and their symbiotic bacteria against the hazelnut weevil Curculio nucum

The virulence of different entomopathogenic nematode strains of the families Steinernematidae and Heterorhabditidae, isolates from Catalonia (NE Iberian Peninsula), and their symbiotic bacteria was assessed with regard to the larvae and adults of the hazelnut weevil, Curculio nucum L. (Coleoptera: Curculionidae). The nematode strains screened included one Steinernema affine, five Steinernema feltiae, one Steinernema carpocapsae, one Steinernema sp. (a new species not yet described) and one Heterorhabditis bacteriophora. The pathogenicity of all the strains of nematodes was tested on larvae and only four of them on adults of the hazelnut weevil. Larval mortality ranged from 10% with S. affine to 79% with Steinernema sp. Adult mortality was higher in S. carpocapsae, achieving 100% adult weevil mortality. The pathogenicity of the symbiotic bacteria Xenorhabdus bovienii, X. kozodoii, X. nematophila and Photorhabdus luminescens was studied in larvae and adults of C. nucum. In the larvae, X. kozodoii showed a LT50 of 22.7 h, and in the adults, it was 20.5 h. All nematodes species except S. affine tested against larvae showed great potential to control the insect, whereas S. carpocapsae was the most effective for controlling adults.     

Stage-specific mortality of Rhagoletis indifferens (Diptera: Tephritidae) exposed to three species of Steinernema nematodes

Mortality of larval, pupal, and adult western cherry fruit fly, Rhagoletis indifferens (Tephritidae) exposed to the steinernematid nematodes Steinernema carpocapsae, Steinernema feltiae, and Steinernema intermedium, was determined in the laboratory and field. Larvae were the most susceptible stage, with mortality in the three nematode treatments ranging from 62 to 100%. S. carpocapsae and S. feltiae were equally effective against larvae at both 50 and 100 infective juveniles (IJs)/cm². S. intermedium was slightly less effective against larvae than the other two species. Mortalities of R. indifferens larvae at 0, 2, 4, and 6 days following their introduction into soil previously treated with S. carpocapsae and S. feltiae at 50 IJs/cm² were 78.6, 92.5, 95.0, and 77.5% and 87.5, 52.5, 92.5, and 70.0%, respectively, and at 100 IJs/cm² were 90.0, 92.0, 100.0, and 84.0% and 90.0, 50.0, 42.0, and 40.0%, respectively. There was no decline in mortality caused by S. carpocapsae as time progressed, whereas there was in one test with S. feltiae. Larval mortalities caused by the two species were the same in a 1:1:1 vermiculite:peat moss:sand soil mix and a more compact silt loam soil. In the field, S. carpocapsae and S. feltiae were equally effective against larvae. Pupae were not infected, but adult flies were infected by all three nematode species in the laboratory. S. carpocapsae was the most effective species at a concentration of 100 IJs/cm² and infected 11–53% of adults that emerged. The high pathogenicity of S. carpocapsae and S. feltiae against R. indifferens larvae and their persistence in soil as well as efficacy in different soil types indicate both nematodes hold promise as effective biological control agents of flies in isolated and abandoned lots or in yards of homeowners.     

Pathogenic effect of entomopathogenic nematode-bacterium complexes on terrestrial isopods

In this study, we evaluated the effect of entomopathogenic nematodes (EPNs) Steinernema carpocapsae, Steinernema feltiae and Heterorhabditis bacteriophora, symbiotically associated with bacteria of the genera Xenorhabdus or Photorhabdus, on the survival of eight terrestrial isopod species. The EPN species S. carpocapsae and H. bacteriophora reduced the survival of six isopod species while S. feltiae reduced survival for two species. Two terrestrial isopod species tested (Armadillidium vulgare and Armadillo officinalis) were found not to be affected by treatment with EPNs while the six other isopod species showed survival reduction with at least one EPN species. By using aposymbiotic S. carpocapsae (i.e. without Xenorhabdus symbionts), we showed that nematodes can be isopod pathogens on their own. Nevertheless, symbiotic nematodes were more pathogenic for isopods than aposymbiotic ones showing that bacteria acted synergistically with their nematodes to kill isopods. By direct injection of entomopathogenic bacteria into isopod hemolymph, we showed that bacteria had a pathogenic effect on terrestrial isopods even if they appeared unable to multiply within isopod hemolymphs. A developmental study of EPNs in isopods showed that two of them (S. carpocapsae and H. bacteriophora) were able to develop while S. feltiae could not. No EPN species were able to produce offspring emerging from isopods. We conclude that EPN and their bacteria can be pathogens for terrestrial isopods but that such hosts represent a reproductive dead-end for them. Thus, terrestrial isopods appear not to be alternative hosts for EPN populations maintained in the absence of insects.     

Combined use of entomopathogenic nematodes and Metarhizium anisopliae as a new approach for black vine weevil,Otiorhynchus sulcatus,control

Combined use of the entomopathogenic nematodes (EPNs), Heterorhabditis bacteriophora Poinar (Heterorhabditidae), Steinernema feltiae Bovien, and Steinernema kraussei Steiner (Steinernematidae) and the insect‐pathogenic fungus, Metarhizium anisopliae (Metsch.) Sorokin (Clavicipitaceae) was evaluated for control of third‐instar black vine weevil, Otiorhynchus sulcatus Fabricius (Coleoptera: Curculionidae). Black vine weevil larvae were exposed to various concentrations of M. anisopliae and EPNs and mortality was assessed weekly or at 3‐day intervals under laboratory and greenhouse conditions. The EPNs were added simultaneously, or 1 or 2 weeks after application of M. anisopliae. Throughout the experiments, the combined application of EPNs with M. anisopliae resulted in increased efficacy against black vine weevil. When the EPNs were applied 1 or 2 weeks after application of the fungus, 100% larval mortality was obtained, even when the biocontrol agents were used at reduced rates. The interactions observed suggest that EPN and M. anisopliae work together synergistically in potted Euonymus fortunei Blondy (Celastraceae) under greenhouse conditions and may provide a powerful and economically feasible approach for black vine weevil larval control.     

Entomopathogenic nematodes control Plum Sawflies (Hoplocampa minuta and H. flava)

Plum sawflies are among the most damaging pests of European plum. Current control strategy implies insecticide application. Three species of entomopathogenic nematodes (EPN), Steinernema feltiae Filipjev, S. carpocapsae Weiser and Heterorhabditis bacteriophora Poinar were tested under laboratory and field conditions to assess effectiveness against larval and adult stages. Laboratory tests resulted in up to 100% mortality of last instar larvae before construction of a cocoon. However, the nematodes were not able to penetrate the cocoon. Foliar application did not result in plum sawflies larvae infestation by EPNs. Under field conditions, the nematodes reduced the number of emerging adults by application against sawfly larvae in the previous year before migration into the soil for overwintering by 62%–92%. Application of the nematodes against adults just before their anticipated emergence resulted in reduction of fruit infestation up to 100%. Mean results of 5 trials using caged trees were 47.8% with S. feltiae, 56.3% with S. carpocapsae and 62.9% with H. bacteriophora. In open field trails, control of adults obtained with S. feltiae at 0.5 million nematodes/m² was 98.2 and 67.8% and at 0.25 million m⁻² 41.7 and 41.2%. Forecasting adult emergence and optimal soil moisture conditions are essential for success of the nematode application.     

Biocontrol of the apple sawfly,Hoplocampa testudinea,with entomogenous nematodes

Four types of experiments were conducted to assess the pathogenicity of entomogenous nematodes against the apple sawfly,Hoplocampa testudinea Klug (Hymenoptera: Tenthredinidae). In Petri dish,Steinernema carpocapsae (Weiser) DD 136 strain,S. carpocapsae All strain,S. feltiae (Filipjev) andHeterorhabditis bacteriophora Poinar caused 100% larval mortality 72 h after the treatments. In semi-field conditions under dwarf apple trees, a single treatment with either 40 or 80S. carpocapsae All strain/cm² caused significant (>80%) larval mortality. No significant increase in mortality was obtained with a second application. In 1990, late treatment with 80S. carpocapsae All strain/cm² caused significant (39.1%) pupal mortality. In 50×50 cm quadrats under dwarf apple trees, treatment with 40 and 80S. carpocapsae All strain/cm² were done in spring 1989. In spring 1990, respectively 22 and 25 apple sawfly adults emerged from quadrats treated with 40 and 80S. carpocapsae All strain/cm², whereas 78 adults emerged from untreated quadrats. In a foliar application experiment, a single treatment withS. carpocapsae All strain significantly reduced the percent of fruit showing secondary damage. The possibility of using entomogenous nematodes as part of an integrated pest management in apple orchards is discussed, with particular reference to the integration of programs aimed at managing plum curculio,Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae) populations.