Pathogenicity,reproduction and foraging behaviours of some entomopathogenic nematodes on a new turf pest,Dorcadion pseudopreissi (Coleoptera: Cerambycidae)

Entomopathogenic nematodes (EPNs) in the families Heterorhabditidae and Steinernematidae have considerable potential as biological control agents of soil-inhabiting insect pests. In the present study, the control potential of the EPNs Steinernema carpocapsae (TUR-S4), S. feltiae (Nemaplus), S. carpocapsae (Nemastar), S. feltiae (TUR-S3) and Heterorhabditis bacteriophora (Nematop) against a new longicorn pest, Dorcadion pseudopreissi Breuning, 1962 (Coleoptera: Cerambycidae), on turf was examined in laboratory studies. Pathogenicity tests were performed at the following doses: 50, 100 and 150 Dauer Juveniles (DJs)/larva at 25°C. Highest mortalities (75–92%) of the larvae were detected at the dose of 150 DJs/larva for all nematodes used. Reproduction capabilities of the used EPNs were examined at doses of 50, 75, 100 and 150 DJs/larva at 25°C. S. carpocapsae (TUR-S4) had the most invasions (32 DJs/larva) and reproduction (28042 DJs/larva) at the dose of 100 DJs, and the highest reproduction (per invaded DJ into a larva) was observed in H. bacteriophora (Nematop) (2402.85 DJs) at a dose of 50 DJs. The foraging behaviour of the nematodes in the presence of D. pseudopreissi and Galleria mellonella L. (Lepidoptera: Galleriidae) larvae was studied using a Petri dish filled with sand at 20°C. All of the used nematodes accumulated near the larvae section of both insect species (32–53% of recovered DJs) with a higher percentage of S. carpocapsae (TUR-S4) (53%) and H. bacteriophora (48%) (Nematop) moving towards larvae of D. pseudopreissi, than the S. feltiae strains.     

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.     

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.     

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.     

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.     

Efficacy of entomopathogenic nematodes against neonate larvae of <Emphasis Type="Italic">Capnodis tenebrionis</Emphasis> (L.) (Coleoptera: Buprestidae) in laboratory trials

The efficacy of five entomopathogenic nematode strains of the families Steinernematidae and Heterorhabditidae was tested against the neonate larvae of Capnodis tenebrionis. The nematode strains screened included two of Steinernema carpocapsae (Exhibit and M137), and one each of S. feltiae (S6), S. arenarium (S2), and Heterorhanditis bacteriophora (P4). Exposure of neonate larvae of Capnodis to 10 and 150 infective juveniles (IJs) per larva (equivalent to 3 and 48 IJs/cm² respectively) in test tubes with sterile sand, resulted in mortality between 60–91% and 96–100%, respectively. At a concentration of 150 IJs/larva, all of the nematode strains were highly virulent. Both S. carpocapsae strains (Exhibit and M137) caused infection and mortality to larvae more quickly than the other strains. However, at a lower concentration assay (10 IJs/larva), S. arenarium was the most virulent strain. The penetration rate as an indicator of entomopathogenic nematode infection was also evaluated. The highest value was recorded for S. arenarium (36%), followed by H. bacteriophora (30.6%), S. feltiae (23.1%), and S. carpocapsae (20.7%).     

Interactions of two idiobiont parasitoids (Hymenoptera: Ichneumonidae) of codling moth (Lepidoptera: Tortricidae) with the entomopathogenic nematode Steinernema carpocapsae (Rhabditida: Steinernematidae)

Simultaneous use of parasitoids and entomopathogenic nematodes for codling moth (CM) control could produce an antagonistic interaction between the two groups resulting in death of the parasitoid larvae. Two ectoparasitic ichneumonid species, Mastrus ridibundus and Liotryphon caudatus, imported for classical biological control of cocooned CM larvae were studied regarding their interactions with Steinernema carpocapsae. Exposure of M. ridibundus and L. caudatus developing larvae to infective juveniles (IJs) of S. carpocapsae (10 IJs/cm2; approximately LC(80-90) for CM larvae) within CM cocoons resulted in 70.7 and 85.2% mortality, respectively. However, diapausing full grown parasitoid larvae were almost completely protected from nematode penetration within their own tightly woven cocoons. M. ridibundus and L. caudatus females were able to detect and avoid ovipositing on nematode-infected cocooned CM moth larvae as early as 12h after treatment of the host with IJs. When given the choice between cardboard substrates containing untreated cocooned CM larvae and those treated with an approximate LC95 of S. carpocapsae IJs (25 IJs/cm2) 12, 24, or 48h earlier, ovipositing parasitoids demonstrated a significant preference for untreated larvae. The ability of these parasitoids to avoid nematode-treated larvae and to seek out and kill cocooned CM larvae that survive nematode treatments enhances the complementarity of entomopathogenic nematodes and M. ridibundus and L. caudatus.     

Predation of entomopathogenic nematodes by <Emphasis Type="Italic">Sancassania</Emphasis> sp. (Acari: Acaridae)

Predation of the entomopathogenic nematode, Steinernema feltiae (Rhabditida: Steinernematidae), by Sancassania sp. (Acari: Acaridae) isolated from field-collected scarab larvae was examined under laboratory conditions. Adult female mites consumed more than 80% of the infective juvenile (IJ) stage of S. feltiae within 24 h. When S. feltiae IJs were exposed to the mites for 24 h and then exposed to Galleria mellonella (Lepidoptera: Pyralidae) larvae, the number of nematodes penetrating into the larvae was significantly lower compared to S. feltiae IJs that were not exposed to mites (control). Soil type significantly affected the predation rate of IJs by the mites. Mites preyed more on nematodes in sandy soil than in loamy soil. We also observed that the mites consumed more S. feltiae IJs than Heterorhabditis bacteriophora (Rhabditida: Heterorhabditidae). No phoretic relationship was observed between mites and nematodes and the nematodes did not infect the mites.     

Food preference of Sancassania polyphyllae (Acari: Acaridae): living entomopathogenic nematodes or insect tissues?

Sancassania polyphyllae (Acari: Acaridae) adult female mites will feed on insect cadavers and infective juveniles (IJs) of entomopathogenic nematodes. Our objective was to determine whether S. polyphyllae has a food preference when offered a choice between tissues of Polyphylla fullo (Coleoptera: Scarabaeidae) or Galleria mellonella (Lepidoptera: Pyralidae), or IJs of Steinernema feltiae (Rhabditida: Steinernematidae) or IJs of Heterorhabditis bacteriophora (Rhabditida: Heterorhabditidae). When offered a choice between no food and one of the different food sources, P. fullo, G. mellonella or S. feltiae IJs, S. polyphyllae had a significant preference for food sources compared to no food. When it was offered either no food or H. bacteriophora, there was no significant difference in the mite distribution. When offered two different food choices, P. fullo or G. mellonella, P. fullo or S. feltiae, and P. fullo or H. bacteriophora, the mite showed significant preferences for P. fullo larvae. In S. feltiae vs. G. mellonella and S. feltiae vs. H. bacteriophora experiments, S. polyphyllae showed significant a preference for S. feltiae. In three-choice experiments, S. polyphyllae had a preference for P. fullo, followed by S. feltiae, G. mellonella and H. bacteriophora, respectively. Our data confirm, in part, our hypothesis that when offered different food choices, this mite species prefers tissues of its phoretic host, P. fullo over lepidopteran host tissues or living IJs. Based on these laboratory data, H. bacteriophora should be used as a biological control agent against P. fullo over a Steinernema species.     

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.     

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.     

Factors affecting entomopathogenic nematodes (Steinernematidae) for control of overwintering codling moth (Lepidoptera: Tortricidae) in fruit bins

Fruit bins infested with diapausing codling moth larvae, Cydia pomonella (L.), are a potential source of reinfestation of orchards and may jeopardize the success of mating disruption programs and other control strategies. Entomopathogenic nematodes (EPNs) were tested as a potential means of control that could be applied at the time bins are submerged in dump tanks. Diapausing cocooned codling moth larvae in miniature fruit bins were highly susceptible to infective juveniles (IJs) of Steinernema carpocapsae (Weiser) and Steinernema feltiae (Filipjev) in a series of experiments. Cocooned larvae are significantly more susceptible to infection than are pupae. Experimental treatment of bins in suspensions of laboratory produced S. feltiae ranging from 10 to 100 IJs/ml of water with wetting agent (Silwet L77) resulted in 51-92% mortality. The use of adjuvants to increase penetration of hibernacula and retard desiccation of S. feltiae in fruit bins resulted in improved efficacy. The combination of a wetting agent (Silwet L77) and humectant (Stockosorb) with 10 S. feltiae IJs/ml in low and high humidity resulted in 92-95% mortality of cocooned codling moth larvae versus 46-57% mortality at the same IJ concentration without adjuvants. Immersion of infested bins in suspensions of commercially produced nematodes ranging from 10 to 50 IJs/ml water with wetting agent in an experimental packing line resulted in mortality in cocooned codling moth larvae of 45-87 and 56 - 85% for S. feltiae and S. carpocapsae, respectively. Our results indicate that EPNs provide an alternative nonchemical means of control that could be applied at the time bins are submerged in dump tanks at the packing house for flotation of fruit.     

Virulence and sex-dependent invasion efficiency of entomopathogenic nematodes on developmental stages of Phthorimaea operculella (Lep., Gelechidae)

Virulence and invasion efficiency of the three entomopathogenic nematodes, Heterorhabditis bacteriophora, Steinernema carpocapsae and S. feltiae against the potato tuber moth (PTM), Phthorimaea operculella was evaluated. Also evaluated were the sex ratio of Steinernema spp. and host stages to determine if 1) the developmental stage of the host affects sex ratio of nematodes; 2) infective juveniles (IJs) concentration affects sex ratio in host developmental stages and 3) the establishment of IJs is affected by developmental stages of host. The PTM pre-pupa and pupa were exposed to IJs in filter substrate petri dish bioassays. By increasing the IJs concentrations, the number of established Steinernema spp. in both PTM stages increased and only decreased at the highest concentration. No reduction in established nematode numbers at the highest concentration was observed for H. bacteriophora. Sex ratio of S. carpocapsae in pre-pupa was affected by IJ concentration. PTM was more susceptible to Steinernema spp. than H. bacteriophora. Pre-pupa were more susceptible to S. feltiae but S. carpocapsae recorded as the most virulent EPN on pupa. Invasion efficiencies were similar for Steinernema and considerably higher than for H. bacteriophora. Despite a higher invasion efficiency of Steinernema into pupae, mortality was lower compared to pre-pupa No correlation was recorded between the invasion efficiencies of the EPNs and mortalities of PTM. The results showed that the invasion efficiency is not appropriate criterion to reflect the virulence of studied EPNs. Compared to H. bacteriophora both tested Steinernema spp. were good candidates for further studies as biocontrol agents of PTM.     

Pathogenicity of three entomopathogenic nematodes against the onion thrips,Thrips tabaci Lind. (Thys.; Thripidae)

Pathogenicity of a native isolate of Steinernema feltiae (H1) and two exotic strains, Heterorhabditis bacteriophora and Steinernema carpocapsae was assessed under laboratory conditions using different concentrations i.e. 4000, 6000, 8000 and 10,000 infective juveniles/ml against second instar larvae, prepupa and pupa of Thrips tabaci Lindeman. The mortality data were recorded 24 and 48?h post-inoculation. The highest mortality rate was recorded for prepupa (62%) than second instar (12.5%) by H. bacteriophora and S. carpocapsae, respectively, 24?h after treatment. No significant differences were found in mortality between prepupa and pupa with increasing the nematodes concentrations (from 4000 to 10,000 nematode/ml) but increasing nematode concentrations increased the mortality of second instar. At the end of the experiment (48?h.), S. feltiae H1 caused the highest mortality on second instar larvae (74%), whereas all other species caused 80–83% mortalities on pupa. This study suggests that native isolate of S. feltiae (H1) had high potential to infect soil-dwelling stages of T. tabaci.     

Biological Control of the Pecan Weevil,Curculio caryae (Coleoptera: Curculionidae), with Entomopathogenic Nematodes

Steinernema carpocapsae (Weiser) strain A11, S. feltiae (Filipjev) strain SN, and Heterorhabditis bacteriophora Poinar strains HP88 and Georgia were tested for their efficacy as biological control agents of the pecan weevil, Curculio caryae (Horn), in pecan orchard soil-profile containers under greenhouse conditions. Percentage C. caryae parasitism by S. carpocapsae and H. bacteriophora strain HP88 and Georgia was consistently poor when applied either prior to or following C. caryae entry into the soil, suggesting that these nematode species and (or) their enterobacteria are poor biological control agents of weevil larvae. Soil taken 21 days following application of S. carpocapsae or H. bacteriophora strain HP88 induced a low rate of infection of Galleria mellonella larvae, whereas soil that had been similarily treated with H. bacteriophora strain Georgia induced a moderate rate of infection. Percentage C. caryae parasitism by S. feltiae was consistently low when applied following C. caryae entry into the soil and was inconsistent when applied as a barrier prior to entry of weevil larvae into the soil. Soil taken 21 days following application of S. feltiae induced a high rate of infection of G. mellonella larvae.     

Influence of humidity and a surfactant-polymer-formulation on the control potential of the entomopathogenic nematode <Emphasis Type="Italic">Steinernema feltiae</Emphasis> against diapausing codling moth larvae (<Emphasis Type="Italic">Cydia pomonella</Emphasis> L.) (Lepidoptera: Tortricidae)

The codling moth (Cydia pomonella L.) is a serious pest of pome fruit. Diapausing cocooned larvae overwinter in cryptic habitats in the soil or in the bark of infested trees. The entomopathogenic nematode Steinernema feltiae (Filipjev) (Rhabditida: Steinernematidae) is used to control diapausing codling moth larvae. The objective of this study was to define environmental conditions favouring the performance of the nematodes. Cocooned larvae were more susceptible than non-cocooned larvae. Susceptibility of pupae was low. To determine the influence of decreasing water activity (a_w-value) on the activity of the nematodes, mortality of codling moth larvae and Galleria mellonella L. were tested in sand-sodium-polyacrylate mixtures of variable water activity. S. feltiae was able to infect both insects at a_w-values >0.9. Cocooned larvae of both insects died at lower a_w-values than non-cocooned larvae. Mortality of cocooned larvae did not further increase after half an hour of exposure to nematodes, whereas the mortality of non-cocooned larvae increased with increasing exposure time. LC₅₀ and LC₉₀ considerably decrease with increasing RH. The negative influence of the relative humidity (macro environment) was less important than the effect of the water activity in the bark substrate (micro environment). The micro environment can be manipulated by applying S. feltiae with higher volumes of water. A surfactant-polymer-formulation significantly increased nematode efficacy and can buffer detrimental environmental effects.     

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.     

Infectivity of Steinernema carpocapsae and S. feltiae to Larvae and Adults of the Hazelnut Weevil,Curculio nucum: Differential Virulence and Entry Routes

We investigated the existing susceptibility differences of the hazelnut weevil, Curculio nucum L. (Coleoptera:, Curculionidae) to entomopathogenic nematodes by assessing the main route of entry of the nematodes, Steinernema carpocapsae strain B14 and S. feltiae strain D114, into larvae and adult insects, as well as host immune response. Our results suggested that S. carpocapsae B14 and S. feltiae D114 primarily entered adult insects and larvae through the anus. Larvae were more susceptible to S. feltiae D114 than S. carpocapsae B14 and adults were highly susceptible to S. carpocapsae B14 but displayed low susceptibility to S. feltiae D114. Penetration rate correlated with nematode virulence. We observed little evidence that hazelnut weevils mounted any cellular immune response toward S. carpocapsae B14 or S. feltiae D114. We conclude the differential susceptibility of hazelnut weevil larvae and adults to S. carpocapsae B14 and S. feltiae D114 primarily reflected differences in the ability of these two nematodes to penetrate the host.     

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.     

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.