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.     

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.     

Laboratory and field evaluation of entomopathogenic nematodes for control of Agriotes obscurus (L.) (Coleoptera: Elateridae)

The susceptibility of the dusky wireworm, Agriotes obscurus (L.) (Coleoptera: Elateridae), to different species and strains of entomopathogenic nematodes was tested in a virulence assay in the laboratory. Larvae were exposed to different nematode doses of 50 and 100 IJs/cm². At a dose of 50 IJs/cm², only a commercial strain Heterorhabditis bacteriophora Poinar and the native strain Steinernema carpocapsae (Weiser) B14 caused increased mortality compared with the control (11.1% and 13.3% mortality, respectively). At the higher dose tested, all strains (except Steinernema sp. D122) were virulent to A. obscurus larvae. Steinernema carpocapsae B14 caused higher mortality of wireworm (75.6%) and was used for the assay conducted in cages, with a dose of 100 IJs/cm², in field conditions. The results showed that S. carpocapsae B14 controlled 48.3% of A. obscurus larvae, demonstrating that some entomopathogenic nematodes have the potential to control larvae of A. obscurus. However, further work is needed to improve their efficacy.     

A chromosome‐level genome assembly of the woolly apple aphid,Eriosoma lanigerum Hausmann (Hemiptera: Aphididae)

Woolly apple aphid (WAA, Eriosoma lanigerum Hausmann) (Hemiptera: Aphididae) is a major pest of apple trees (Malus domestica, order Rosales) and is critical to the economics of the apple industry in most parts of the world. Here, we generated a chromosome‐level genome assembly of WAA—representing the first genome sequence from the aphid subfamily Eriosomatinae—using a combination of 10X Genomics linked‐reads and in vivo Hi‐C data. The final genome assembly is 327 Mb, with 91% of the assembled sequences anchored into six chromosomes. The contig and scaffold N50 values are 158 kb and 71 Mb, respectively, and we predicted a total of 28,186 protein‐coding genes. The assembly is highly complete, including 97% of conserved arthropod single‐copy orthologues based on Benchmarking Universal Single‐Copy Orthologs (busco ) analysis. Phylogenomic analysis of WAA and nine previously published aphid genomes, spanning four aphid tribes and three subfamilies, reveals that the tribe Eriosomatini (represented by WAA) is recovered as a sister group to Aphidini + Macrosiphini (subfamily Aphidinae). We identified syntenic blocks of genes between our WAA assembly and the genomes of other aphid species and find that two WAA chromosomes (El5 and El6) map to the conserved Macrosiphini and Aphidini X chromosome. Our high‐quality WAA genome assembly and annotation provides a valuable resource for research in a broad range of areas such as comparative and population genomics, insect–plant interactions and pest resistance management.     

Susceptibility of Oriental armyworm,Mythimna separata (Lepidoptera: Noctuidae) larvae and pupae to native entomopathogenic nematodes

The Oriental armyworm, Mythimna separata Walker (Lepidoptera: Noctuidae) is a major pest of cereal crops, and its outbreaks result in complete crop loss. In this study, we tested the pathogenicity and reproductive potential of indigenous entomopathogenic nematodes (EPNs), Heterorhabditis indica Poinar, Karunakar, & David NBAIIH38, Steinernema abbasi Elawad NBAIISa01, S. carpocapsae Weiser NBAIISc05 and S. siamkayai Stock, Somsook and Reid NBAIRS92 against larval and pupal stages of M. separata under laboratory conditions. Steinernema carpocapsae caused significantly greater mortality in second- and fourth-instar larval stages than other EPNs species. Steinernema carpocapsae caused greatest mortality 100% in larval stages and 75% in pupal stages. Significant differences were observed in the lethal concentration values (LC₅₀ and LC₉₀) of EPNs species against different stages of M. separata. Differences in penetration and multiplication in the fourth-instar larval stages of M. separata were observed amongst the EPNs species. However, further studies are needed to reveal the field performance of EPN isolates tested to be included in the IPM programme of M. separata.     

The combined effect of soil‐applied azadirachtin with entomopathogens for integrated management of western flower thrips

Performance of soil application of azadirachtin products with entomopathogens was evaluated as single treatments, in multiple combinations and in different concentrations against the soil stages of western flower thrips, Frankliniella occidentalis (Pergande), in French beans Phaseolus vulgaris L. Treatments consisted of NeemAzal‐T solution, neem pellets, Steinernema carpocapsae (Weiser) Nemastar^®, isolates of Metarhizium anisopliae (Metschnikoff) Sorokin (IPP 2539 and ICIPE‐69) and Beauveria bassiana (Balsamo) – Naturalis^®. All treatments were analysed for the number of emerging adults, while emerged adults in fungi‐based treatments were analysed additionally for the retarded development of mycosis as a possible cause of secondary mortality. Possible interactive effects in combined treatments were analysed using a generalized linear model (GLM) approach, and three levels of dose–response combinations of the selected treatments were further tested. Bioassay results of the single treatments indicated between 43% and 60% reduction in adult emergence with NeemAzal‐T solution thus proving to be the most efficient. However, most cadavers with entomopathogenic fungi (EPF) treatments showed the development of mycosis. Therefore, the reduction in adult emergence attributed to the EPF was altogether >87%. Combined treatments with Steinernema, Metarhizium (ICIPE‐69), NeemAzal‐T and neem pellets resulted in total reduction in adult emergence of 95–97% when late mortality by mycosis was considered. Of the treatment combinations, two showed synergistic, four additive and one an antagonistic response. Combining low concentration of entomopathogenic nematode (EPN) (100 IJ/cm²) with NeemAzal‐T resulted in satisfactory control compared to the operational dose of EPN, while the highest concentration of M. anisopliae (10⁸ conidia) combined with Steinernema showed the best performance with 74% reduction in adult emergence.     

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.     

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.     

Entomopathogenic nematodes as potential biological control agents of Popillia japonica (Coleoptera,Scarabaeidae) in Piedmont Region (Italy)

In 2014, the Japanese beetle Popillia japonica (Coleoptera: Scarabaeidae) was first spotted in northern Italy in the Nature Park of the Ticino Valley, its first detection in continental Europe. This polyphagous invasive species has the potential to cause serious losses to horticulture and agriculture. Particularly for its management in a Nature Park, environmentally friendly strategies are necessary. To develop baseline data for a biological control approach to the Italian outbreak of P. japonica, we conducted laboratory and field experiments testing several indigenous and commercial strains of the entomopathogenic nematode (EPN) species Heterorhabditis bacteriophora and Steinernema carpocapsae against P. japonica larvae. In the laboratory, strains of H. bacteriophora caused greater mortality (ranging from 57% to 100%) than those of S. carpocapsae (3% to 77%). In micro‐plot field tests carried out at three different times, the most virulent indigenous EPN strain, H. bacteriophora ItH‐LU1, showed again the best results ranging from 44% to 93% against young larvae. Finally, in a large‐plot field trial, the commercial H. bacteriophora product provided 46% larval mortality. This study shows that H. bacteriophora strains have good potential as biological control agents of larvae of the invasive P. japonica in northern Italy.     

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.     

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.     

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.     

Effect of potting media on the efficacy and dispersal of entomopathogenic nematodes for the control of black vine weevil, Otiorhynchus sulcatus (Coleoptera: Curculionidae)

The effect of five commercial potting media, peat, bark, coir, and peat blended with 10% and 20% compost green waste (CGW) on the virulence of six commercially available entomopathogenic nematodes (EPN), Heterorhabditis bacteriophora UWS1, Heterorhabditis megidis, Heterorhabditis downesi, Steinernema feltiae, Steinernema carpocapsae, and Steinernema kraussei was tested against third-instar black vine weevil (BVW), Otiorhynchus sulcatus. Media type was shown to significantly affect EPN virulence. Heterorhabditis species caused 100% larval mortality in all media whereas Steinernema species caused 100% larval mortality only in the peat blended with 20% CGW. A later experiment investigated the effect of potting media on the virulence of EPN species against BVW by comparing the vertical dispersal of EPN in the presence and absence of BVW larva. Media type significantly influenced EPN dispersal. Dispersal of H. bacteriophora was higher than H. megidis, H. downesi, or S. kraussei in all media, whereas, S. feltiae and S. carpocapsae dispersal was much reduced and restricted to peat blended with 20% CGW and coir, respectively. In the absence of larvae, most of the EPN species remained in the same segment they were applied in, suggesting that the larvae responded to host volatile cues. Greenhouse trials were conducted to evaluate the efficacy of most virulent strain, H. bacteriophora in conditions more representative of those in the field, using 2.5 × 10⁹ infective juveniles/ha. The efficacy of H. bacteriophora UWS1 against third-instar BVW was 100% in peat, and peat blended with 10% and 20% CGW but only 70% in bark and coir, 2 weeks after application. These studies suggest that potting media significantly affects the efficacy and dispersal of EPN for BVW control.     

Modulation of immune responses of Rhynchophorus ferrugineus (Insecta: Coleoptera) induced by the entomopathogenic nematode Steinernema carpocapsae (Nematoda: Rhabditida)

Aim of this study was to investigate relationships between the red palm weevil (RPW) Rhynchophorus ferrugineus (Olivier) and the entomopathogenic nematode Steinernema carpocapsae (EPN); particularly, the work was focused on the immune response of the insect host in naive larvae and after infection with the EPN. Two main immunological processes have been addressed: the activity and modulation of host prophenoloxidase‐phenoloxidase (proPO) system, involved in melanization of not‐self and hemocytes recognition processes responsible for not‐self encapsulation. Moreover, immune depressive and immune evasive strategies of the parasite have been investigated. Our results suggest that RPW possess an efficient immune system, however in the early phase of infection, S. carpocapsae induces a strong inhibition of the host proPO system. In addition, host cell‐mediated mechanisms of encapsulation, are completely avoided by the parasite, the elusive strategies of S. carpocapsae seem to be related to the structure of its body‐surface, since induced alterations of the parasite cuticle resulted in the loss of its mimetic properties. S. carpocapsae before the release of its symbiotic bacteria, depress and elude RPW immune defenses, with the aim to arrange a favorable environment for its bacteria responsible of the septicemic death of the insect target.     

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.     

Comparative study of entomopathogenic nematode isolation using Galleria mellonella (Pyralidae) and Spodoptera littoralis (Noctuidae) as baits

Entomopathogenic nematode (EPN) occurrence in soil from natural areas and crop field edges from La Rioja (northern Spain) was compared using two insects as baits: Galleria mellonella (Lepidoptera: Pyralidae) and Spodoptera littoralis (Lepidoptera: Noctuidae). Both insects trapped Steinernema feltiae, S. kraussei and S. carpocapsae, with G. mellonella being more efficient than S. littoralis recording 5.4 and 2.6% of positive soil samples, respectively. EPN recovery frequency and abundance obtained with G. mellonella were not statistically different between natural and crop field edges values; however, S. littoralis was more successful trapping EPNs from crop field edges. Statistical differences were observed for recovery frequency recorded by both hosts in natural areas. Significant differences in larval mortality between both insects were not observed. The use of S. littoralis in entomopathogenic nematode surveys is discussed.     

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.     

Characterization of biocontrol traits in the entomopathogenic nematode Heterorhabditis georgiana (Kesha strain), and phylogenetic analysis of the nematode’s symbiotic bacteria

Our objective was to estimate the biocontrol potential of the recently discovered entomopathogenic nematode species Heterorhabditis georgiana (Kesha strain). Additionally, we conducted a phylogenetic characterization of the nematode’s symbiotic bacterium. In laboratory experiments, we compared H. georgiana to other entomopathogenic nematodes for virulence, environmental tolerance (to heat, desiccation, and cold), and host seeking ability. Virulence assays targeted Acheta domesticus, Agrotis ipsilon, Diaprepes abbreviatus, Musca domestica, Plodia interpunctella, Solenopsis invicta, and Tenebrio molitor. Each assay included H. georgiana and five or six of the following species: Heterorhabditis floridensis, Heterorhabditis indica, Heterorhabditis mexicana, Steinernema carpocapsae, Steinernema feltiae, Steinernema rarum, and Steinernema riobrave. Environmental tolerance assays included Heterorhabditis bacteriophora, H. georgiana, H. indica, S. carpocapsae, S. feltiae, and S. riobrave (except cold tolerance did not include S. carpocapsae or S. riobrave). Host seeking ability was assessed in H. bacteriophora, H. georgiana, S. carpocapsae, and Steinernema glaseri, all of which showed positive orientation to the host with S. glaseri having greater movement toward the host than S. carpocapsae (and the heterorhabditids being intermediate). Temperature range data (tested at 10, 13, 17, 25, 30 and 35 °C) indicated that H. georgiana can infect Galleria mellonella between 13 and 35 °C (with higher infection at 17–30 °C), and could reproduce between 17 and 30 °C (with higher nematode yields at 25 °C). Compared with other nematode species, H. georgiana expressed low or intermediate capabilities in all virulence and environmental tolerance assays indicating a relatively low biocontrol potential. Some novel observations resulted from comparisons among other species tested. In virulence assays, H. indica caused the highest mortality in P. interpunctella followed by S. riobrave; S. carpocapsae caused the highest mortality in A. domesticus followed by H. indica; and S. riobrave was the most virulent nematode to S. invicta. In cold tolerance, S. feltiae exhibited superior ability to cause mortality in G. mellonella (100%) at 10 °C, yet H. bacteriophora and H. georgiana exhibited the ability to produce attenuated infections at 10 °C, i.e., the infections resumed and produced mortality at 25 °C. In contrast, H. indica did not show an ability to cause attenuated infections. Based on the phylogenetic analysis, the bacterium associated with H. georgiana was identified as Photorhabdus luminescens akhurstii.     

Control of the Oriental Fruit Moth, Grapholita molesta, Using Entomopathogenic Nematodes in Laboratory and Fruit Bin Assays

The oriental fruit moth (OFM), Grapholita molesta (Busck), which is among the most important insect pests of peaches and nectarines, has developed resistance to a wide range of insecticides. We investigated the ability of the entomopathogenic nematodes (EPN) Steinernema carpocapsae (Weiser), S. feltiae (Filipjev), S. riobrave (Cabanillas et al.), and Heterorhabditis marelatus (Liu and Berry) to control OFM under laboratory and fruit bin conditions. At a dosage of 10 infective juveniles (IJ)/cm² in the laboratory, S. carpocapsae caused 63%, S. feltiae 87.8%, S. riobrave 75.6%, and H. marelatus 67.1% OFM mortality. All four nematode species caused significant OFM larval mortality in comparison to the nontreated controls. Steinernema feltiae was used for the bin assays due to the higher OFM mortality it caused than the other tested EPN species and to its ability to find OFM under cryptic environments. Diapausing cocooned OFM larvae in miniature fruit bins were susceptible to IJ of S. feltiae in infested corner supports and cardboard strips. Treatment of bins with suspensions of 10 or 25 S. feltiae IJ/ml water with wetting agent (Silwet L77) resulted in 33.3 to 59% and 77.7 to 81.6% OFM mortality in corner supports and cardboard strips, respectively. This paper presents new information on the use of EPN, specifically S. feltiae, as nonchemical means of OFM control.     

Entomopathogenic Nematodes for Control of Codling Moth,Cydia pomonella(Lepidoptera: Tortricidae): Effect of Nematode Species, Concentration, Temperature, and Humidity

The susceptibility of codling moth diapausing larvae to three entomopathogenic nematode species was assessed in the laboratory using a bioassay system that employed cocooned larvae within cardboard strips. The LC₅₀values forSteinernema carpocapsae, S. riobrave,andHeterorhabditis bacteriophorawere 4.7, 4.8, and 6.0 infective juveniles/cm², respectively. When a discriminating concentration of 10 infective juveniles/cm²of each of the three nematode species was evaluated at 15, 20, 25, and 30°C,S. carpocapsaewas the most effective nematode with mortalities ranging from 66 to 90%. Mortalities produced byS. riobraveandH. bacteriophoraat the four temperatures were 2–94 and 25–69%, respectively. Studies were also conducted to test infectivity at 10, 35, and 40°C. No mortality was produced by any of the nematode species at 10°C.S. riobravewas the most infective nematode at 35°C producing 68% mortality which was more than twice that observed forS. carpocapsaeorH. bacteriophora.Codling moth larvae treated with 10 infective juveniles/cm²ofS. carpocapsaeand kept in 95+% RH at 25°C for 0–24 h followed by incubation at 25–35% RH indicated that more than 3 h in high humidity was needed to attain 50% mortality. Trials ofS. carpocapsae, S. riobrave,andH. bacteriophoraat 50 infective juveniles/cm²against cocooned larvae on pear and apple logs resulted in reductions of codling moth adult emergence of 83, 31, and 43%, respectively, relative to control emergence. Trials of the three entomopathogenic nematodes at 50 infective juveniles/cm²against cocooned larvae in leaf litter resulted in 99 (S. carpocapsae), 80 (S. riobrave), and 83% (H. bacteriophora) mortality, respectively. Our results indicate good potential of entomopathogenic nematodes, especiallyS. carpocapsae,for codling moth control under a variety of environmental conditions.