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Laboratory bioassays were conducted to evaluate the interactions between an entomopathogenic nematode (EPN), Steinernema carpocapsae (Nematoda: Steinernematidae), and the insecticide abamectin against the Potato tuber moth (PTM), Phthorimaea operculella, one of the key insect pests of potatoes (Solanum tuberosum). Steinernema carpocapsae was highly virulent against pre-pupae but significantly less virulent against pupae with respective LC50 values of 10.5 and 102.1 infective juvenile nematodes (IJs) per individual. Abamectin was similarly toxic to pre-pupae and pupae with respective LC50 values of 25.3 and 28.0 ppm. However, abamectin had detrimental effects on S. carpocapsae IJs causing up to 70% mortality when they were exposed at 1000 ppm for 24 h. PTM life stage had a strong effect on insect mortality when exposed to combinations of S. carpocapsae and abamectin. Against pre-pupae, combinations mostly had a synergistic effect on mortality with the exceptions being additive; against pupae, combinations mostly had an antagonistic effect on mortality with the exceptions being additive. The synergistic interaction in pre-pupae was the strongest and the antagonistic interaction in pupae the weakest when the combinations included the lowest abamectin rate (LC10) which can be explained by the more limited negative effect of the lower abamectin rate on the IJs. The synergistic interaction and the negative effect of higher abamectin rates on it were confirmed in a greenhouse experiment on potato plants. Combinations of abamectin and S. carpocapsae have potential for the control PTM and could help reduce to usage of synthetic insecticides in PTM management.

Entomopathogenic nematodes are used widely in biological insect control. Entomopathogenic nematodes can infect live insects as well as dead insects (i.e., they can act as scavengers). It is important to determine compatibility of entomopathogenic nematodes with other pest management tactics such as chemical insecticides. We hypothesized that chemical insecticides have negative impact on scavenging nematodes. According to our hypothesis, we first investigated the effects of direct exposure of Steinernema carpocapsae infectivity juveniles (IJs) to three chemical insecticides, cypermethrin, spinosad or diflubenzuron in terms of nematode survival and virulence. Subsequently, using the same chemicals, we tested the effects of insecticide-killed insects on scavenger nematode penetration efficiency, time of emergence and the number of nematode progeny. Prior to our study, the impact of pesticides on scavenger nematode fitness had not been studied. Fall webworm, Hyphantria cunea, and greater wax moth, Galleria mellonella, larvae were used as host insects. The survival rate of IJs after direct exposure was 83% for cypermethrin and 93-97% for the other insecticides and control. There were no significant differences in the survival and virulence of the nematodes after 24 h exposure to insecticides. The number of nematodes that invaded the insecticide-killed host was significantly higher in cypermethrin and spinosad treated groups and live H. cunea than in the diflubenzoron treated group and freeze-killed control. However, no significant differences were observed in time of emergence. Significantly more progeny IJs emerged from Spinosadkilled insects than the freeze-killed control. In conclusion, we discovered that the fitness of scavenging IJs is not diminished by insecticides in insect cadavers. In fact, in some cases the exposure to chemical insecticides may enhance virulence. WOS:000694716200010 2-s2.0-85108913403 PubMed: 34186086

The relatively short shelf life of many entomopathogenic nematode (EPN) based products is a major constraint which limits their widespread usage in IPM programs. The two primary factors that affect survival of the infective juveniles (IJs) during storage (i.e. shelf life) are the rate at which the IJs utilize their energy reservoirs during storage and the effect of microbial contamination in formulation. In the present study, the suitability of Carboxymethyl cellulose (CMC) as an inert substrate for EPNs formulation was evaluated. Survival and virulence of dehydrated and non-dehydrated CMC formulated IJs of Heterorhabditis bacteriophora and Steinernema carpocapsae in the presence and absence of an antimicrobial agent was evaluated at two temperatures, 15 and 25 °C, over a six-month storage period. After six months of storage at 25 °C, levels of survival of H. bacteriophora and S. carpocapsae (77% and 93%, respectively) were highest where dehydrated IJs where in CMC which contained an antimicrobial agent. The effect of storage temperature (15 versus 25 °C) with respect to this formulation was species specific: a significant effect was seen in the case of H. bacteriophora, though not for S. carpocapsae. In both species, efficacy of anhydrobiosis on IJs survival emerged as foraging strategy dependent factor; this situation was observed for the efficacy of formaldehyde too. EPNs mortality across all treatments revealed two-stage survival curves, stage I with a steep slope and high mortality rate and stage II with a gentle slope and low rate of mortality. In our results CMC emerged as an efficient substrate for formulation of evaluated EPNs, mainly S. carpocapsae, though the use of antimicrobial agents other than formaldehyde may also make this formulation tool more appropriate for H. bacteriophora. Regarding the two-stage model, we propose that when assessing the suitability of new isolates for mass production, screening IJs from the 2nd stage of this mortality curves could be useful in terms of predicting the long-term viability of EPNs-based products.

Six entomopathogenic nematode species (EPNs) ( Heterorhabditis bacteriophora H06 (H06), Steinernema carpocapsae NC116 (NC116), Steinernema carpocapsae All (All), Steinernema longicaudum X-7 (X-7), Steinernema feltiae SF-SN (Sf) and Heterorhabditis indica LN 2 (LN 2 ) were tested for virulence against 3rd instar Bradysia odoriphaga , and their interactions with thiamethoxam against 3rd instar B. odoriphaga under laboratory and greenhouse conditions were also evaluated. S. feltiae SF-SN, which is the most virulent, was selected to evaluate the synergism effects with thiamethoxam at different concentrations under laboratory conditions. S. feltiae SF-SN and thiamethoxam were either applied alone or in combination, and the combined application manner was evaluated in the greenhouse. Under laboratory conditions, a synergistic effect was found between six EPNs and thiamethoxam. The combination effects of Sf, All and LN 2 species caused significantly higher mortality than the other three treatments (X-7, H06 and NC116). Furthermore, the combination of Sf and All species led to a significantly higher control effect than LN 2 in greenhouse tests. In further greenhouse tests, the combination effect of Sf (0.75 billion IJs/ha) + thiamethoxam (1.0 kg a.i./ha) applied twice (28 day intervals) was significantly higher than a single treatment of Sf + thiamethoxam at twice the dosage. Compared to the single thiamethoxam application, the combination effects of Sf and thiamethoxam had the highest value at over 90% of the control effects for up to 6 weeks. Therefore, the integrated technique of the synergism of S. feltiae SF-SN species and thiamethoxam to control B. odoriphaga could be useful for integrated pest management in the future.

Relationships between parasites and hosts can be drastic, depending on the balance between parasite strategies and the efficiency of the host immune response. In the case of entomopathogenic nematodes and their insect hosts, we must also consider the role of bacterial symbionts, as the interaction among them is tripartite and each component plays a critical role in death or survival. We analyzed the effects induced by the nematode–bacteria complex Steinernema carpocapsae, against red palm weevil (RPW) larvae, Rhynchophorus ferrugineus. We examined the antimicrobial response of the insect when in the presence of nematocomplexes or of its symbionts, Xenorhabdus nematophila. In detail, we investigated the potential interference of live and dead S. carpocapsae, their isolated cuticles, live or dead bacterial symbionts and their lipopolysaccharides, on the synthesis and activity of host antimicrobial peptides. Our data indicate that both live nematodes and live bacterial symbionts are able to depress the host antimicrobial response. When nematodes or symbionts were killed, they lacked inhibitory properties, as detected by the presence of antimicrobial peptides (AMPs) in the host hemolymph and by assays of antimicrobial activity. Moreover, we isolated S. carpocapsae cuticles; when cuticles were injected into hosts they revealed evasive properties because they were not immunogenic and were not recognized by the host immune system. We observed that weevil AMPs did not damage X. nematophila, and the lipopolysaccharides purified from symbionts seemed to be non-immunogenic. We believe that our data provide more information on the biology of entomopathogenic nematodes, in particular concerning their role and the activity mediated by symbionts in the relationship with insect hosts.

TheSteinernema carpocapsae-Xenorhabdus nematophilaassociation is a nematobacterial complex (NBC) used in biological control of insect crop pests. The ability of this dual pathogen to infest and kill an insect strongly depends on the dialogue between the host’s immune system and each partner of the complex. Even though this dialogue has been extensively studied from the two partners’ points of view in several insect models, still little is known about the structure and the molecular aspects of the insects’ immune response to the dual infection. Here, we used the lepidopteran pestSpodoptera frugiperdaas a model to analyze the respective impact of each NBC partner in the spatiotemporal immune responses that are induced after infestation. To this aim, we first analyzed the expression variations of the insect’s immune genes in the fat bodies and hemocytes of infested larvae by using previously obtained RNAseq data. We then selected representative immune genes for RT-qPCR investigations of the temporal variations of their expressions after infestation and of their induction levels after independent injections of each partner. We found that the fat body and the hemocytes both produce potent and stable immune responses to the infestation by the NBC, which correspond to combinations of bacterium- and nematode-induced ones. Consistent with the nature of each pathogen, we showed thatX. nematophilamainly induces genes classically involved in antibacterial responses, whereasS. carpocapsaeis responsible for the induction of lectins and of genes expected to be involved in melanization and cellular encapsulation. In addition, we found that two clusters of unknown genes dramatically induced by the NBC also present partner-specific induction profiles, which paves the way for their functional characterization. Finally, we discuss putative relationships between the variations of the expression of some immune genes and the NBC’s immunosuppressive strategies.Author summaryEntomopathogenic nematodes (EPNs) are living in the soil and prey upon insect larvae. They enter the insect by the natural orifices, and reach the hemocoel through the intestinal epithelium. There, they release their symbiotic bacteria that will develop within the insect and eventually kill it. Nematodes can then feed and reproduce on the insect cadaver. By using transcriptomic approaches, we previously showed that Lepidoptera larvae (caterpillars of the fall armywormSpodoptera frugiperda) produce a strong immune response in reaction to infestation by EPNs. However, we do not know if this immune reaction is triggered by the nematode itself -Steinernema carpacapsae- or its symbiotic bacteria -Xenorhabdus nematophila. To answer this question, we present in this work a careful annotation of immunity genes inS. frugiperdaand surveyed their activation by quantitative PCR in reaction to an injection of the bacteria alone, the axenic nematode or the associated complex. We found that the immune genes are selectively activated by either the bacteria or the nematode and we discuss the implication of which pathway are involved in the defense against various pathogens. We also show that a cluster of newly discovered genes, present only in Lepidoptera, is activated by the nematode only and could represent nematicide genes.

Wireworms, the larval stage of click beetles (Coleoptera: Elateridae), are economically important soil-dwelling pests that attack many field crops worldwide. Wireworms have become a serious threat to spring wheat in the Northern Great Plains because of lack of effective control measures, creating a need for alternative control methods such as biological control with entomopathogenic nematodes (EPNs). A laboratory bioassay was used to test ten EPN strains and identify infective EPN strains against the sugarbeet wireworm, Limonius californicus (Mannerheim) (Coleoptera: Elateridae). Steinernema carpocapsae (Weiser) (All and Cxrd strains) and S. riobrave Cabanillas, Poinar, and Raulston (355 and 7–12 strains) killed 60–70% of L. californicus larvae in four weeks when applied at 700 Infective juveniles (IJs) (25 IJs/cm2), 1400 IJs (50 IJs/cm2), 2800 IJs (100 IJs/cm2), and 5600 IJs (200 IJs/cm2) per larva in the laboratory. Also, Heterorhabditis bacteriophora (Poinar) VS strain and Steinernema rarum (Doucet) 17c + e strain caused 50–60% mortality to L. californicus larvae after four weeks when applied at 5600 IJs/larva. However, regardless of the concentration applied, the penetration rate of infective juveniles into the host did not exceed 33%. In shade house trials, S. riobrave and S. carpocapsae strains caused 34–56% L. californicus mortality after four weeks with 50 and 56% mortality caused by S. carpocapsae All and S. riobrave 355 strain, respectively when applied at the rate of 80,000 IJs/pot. These results suggest that S. carpocapsae and S. riobrave may have significant potential for protecting spring wheat crops from L. californicus.

The rose sawfly, Arge ochropus (Gmelin), is one of the most destructive pests attacking rose bushes in northern Iran. In the present study, the haemocyte reactions of A. ochropus larvae were assessed against two entomopathogenic nematodes, Steinernema carpocapsae (Weiser) and Heterorhabditis bacteriophora Poinar. With injection of infective juveniles of H. bactriophora into A. ochropus larvae, the total haemocyte count showed alternating fluctuations at all time intervals. Encapsulation occurred 22 hours post injection (hpi) of H. bacteriophora infective juveniles into the rose sawfly larvae, while melanization was observed after 24 h. In the case of S. carpocapsae, initial attachment of the haemocytes was detected at 18 hpi and complete encapsulation at 24 hpi; no melanization was observed. In general, findings showed strong immune responses of the rose sawfly larvae against H. bacteriophora, while these reactions were weakened for S. carpocapsae. Therefore, it is concluded that S. carpocapsae has more ability to overcome the host defence system, and this research provides a new window on its potential as a biocontrol agent.

The efficiency of entomopathogenic fungi, Beauveria bassiana and Entomophthora sp. as well as the nematode, Steinernema carpocapsae, against 3rd, 5th instar nymphs and adults of the desert locust, Schistocerca gregaria (Forskal) had been studied under laboratory conditions. Fungi at the concentrations 2.3 × 105, 7 × 107, 3.9 × 109 and 4 × 105, 6.7 × 107, 2.2 × 109 spores/ml and nematode at 5000, 2500, 1250 IJS/ml, respectively were applied on the desert locust by two different treatment methods; spray and soil application. The obtained results revealed that all the locust nymphs and adults were susceptible to fungi and nematode with high mortality rate records. The nematode killed approximately 100% of the tested locust individuals within 3–5 days postinfection and was found more effective than fungi in less time. On the other hand entomopathogenic fungi and nematode were found to be more effective when applied on the soil surface rather than spray treatment. This was common at any concentration used. Based on mortality percentages, all tested fungi and nematode had high potentials for biocontrol agents against S. gregaria.

The ultrastructure studies on the haemolymph of 5th larval instar of Galleria mellonella showed five types of haemocytes; Prohaemocytes, Plasmatocytes, Granulocytes, Oenocytoids and Spherulocytes. After treatment with Steinernema carpocapsae BA2, the haemocytes underwent considerable structural changes. More destructive effects were observed in the haemocytes of G. mellonella treated with gamma irradiated S. carpocapsae.

Entomopathogenic nematodes have a broad range of insect hosts, but efficacy varies depending on many factors including insect species and life stage of the host. In this study we examined the susceptibility of males and females of two insect species, the American cockroach Periplaneta americana and the flatheaded rootborer Capnodis tenebrionis to Steinernema carpocapsae by exposing adults to different concentrations. A separate study examined the routes of entry used by nematodes into males and females. Males of both species were more susceptible than females, with greater than 97% infection when a concentration of 50 IJs/cm(2) was applied, whereas mortalities lower than 58% were achieved against females 14 days post-infection. Infective juveniles were detected in similar number on the surface of both sexes, but when compared among internal regions the number of nematodes was significantly higher in gonads and ducts of males than of females for P. americana (5.49 in males; 0.02 in females) and C. tenebrionis (6.88 in males; 0.00 in females).

The submerged monoxenic culture of the entomopathogenic nematode, Steinernema carpocapsae CABA01, was carried out in two internal-loop airlift reactors (R1 and R2) with some geometric differences. Two runs each reactor were carried out at operating conditions VL = 4.22 L, Q = 1–1.5 vvm, T = 22 °C. The culture broth apparent viscosity changed from 2 to 12 mPa s determining global changes in both hydrodynamics (expressed as the dimensionless Reynolds number, Re) and oxygen transfer conditions (expressed as the kLa coefficient). Such changes were 170

To assess the potential for marketing pre-amended plant growing media, we compared survival of the entomopathogenic nematodes, Steinernema carpocapsae, delivered via Galleria mellonella and Tenebrio molitor cadavers in the Scotts commercial growing medium, Miracle-Gro®. Six pouches, each filled with 10 g of the growing medium containing 6 nematode-infected cadavers of either insect species were placed in each 1 kg Miracle-Gro® bag. The nematode survival was assessed in the cadavers, pouches and the bags. Although, overall survival of S. carpocapsae declined within 90 days in both cadaver types, survival was significantly higher in G. mellonella than T. molitor cadavers at 15, 45, 60 and 90 days most likely due to the higher reproduction in G. mellonella cadavers. Similarly, survival (assessed as the number of baited G. mellonella killed) remained consistently higher both in the pouches and bags in the G. mellonella cadaver treatment compared to the T. molitor treatment. In another experiment in which bags were not opened until 180 days, all G. mellonella cadavers disintegrated within 180 days of storage; however, the number of baited G. mellonella larvae killed in the pouch was similar in both the cadaver treatments indicating equal number of surviving nematodes. Further, we evaluated the effect of initial moisture content of the growing medium on the survival and virulence of nematodes when delivered through cadavers and aqueous suspension. The results showed that survival and virulence of S. carpocapsae was higher in G. mellonella cadaver treatment than in the aqueous suspension treatment at all sampling times, and reducing the initial moisture content of the medium from 50% to 20–30% enhanced nematode survival in the medium. This is the first report demonstrating the possibility of directly delivering entomopathogenic nematodes through commercial growing medium via infected insect cadavers, a method in which nematode survival could be further enhanced by reducing the initial moisture content of the growing medium.

Steinernematid nematodes are parasites that are important natural regulating agents of insect populations. The infective juvenile nematodes respond to a variety of stimuli that aid in survival and host finding. Host finding strategies among steinernematids differ along a continuum from ambush (sit & wait) to cruiser (search & destroy). In this paper we describe directional movement in response to an electrical current, which was generated on agar plates. Specifically, Steinernema glaseri (a cruiser) moved to a higher electric potential, whereas Steinernema carpocapsae, an ambusher, moved to a lower electric potential. Thus, we hypothesize that steinernematids may detect electrical currents or electromagnetic fields in nature, and these stimuli may be used differentially among species for host finding or enhancing other fitness characters.

We conducted a study to determine the relationship between turfgrass management intensity and natural occurrence of entomopathogenic nematodes (EPNs). We surveyed for EPNs on putting greens, fairways, and rough areas—three distinct surface types on golf courses that are managed with different intensities. We collected 159 soil samples from putting greens, contiguous fairways, and rough areas from 19 golf courses in Ohio, USA. Nematodes were recovered from soil samples using the insect baiting technique. We also analyzed the soil samples for texture, organic matter, pH, phosphorus, calcium, magnesium and potassium. We used principal components analysis and Pearson correlation to determine the relationship between nematode occurrence and the measured parameters. Surface type was the most important factor in predicting EPNs occurrence. Putting greens differed significantly from fairways and rough areas in the number of EPN-positive sites. No EPNs were recovered from putting greens but were recovered from 43% of the fairways and 57% of the rough areas. Putting greens also differed significantly from fairways and rough areas in organic matter, pH, calcium, and phosphorus. The fairways and rough areas did not however differ in number of EPN-positive sites and measured soil parameters. Presence of EPNs correlated significantly, although weakly, with sand, silt, phosphorus, organic matter, and magnesium content, but not with clay, pH, calcium, and potassium. Nematode isolates were identified as Heterorhabditis bacteriophora , Steinernema carpocapsae , and S. glaseri . This suggests that EPNs are more likely to occur in less intensively managed sites that receive fewer inputs and have relatively high sand, and moderate silt, organic matter, phosphorus, and magnesium content.

For the use of the entomopathogenic nematode Steinernema carpocapsae on cabbage foliage to control larvae of the diamondback moth (DBM), Plutella xylostella, a formulation containing 0.3% of the surfactant Rimulgan and 0.3% of the polymer xanthan was tested in leaf bioassays and compared to nematodes applied in water. Compared to water, the surfactant–polymer formulation (SPF) significantly improved efficacy. Using 75 dauer juveniles (DJs) cm−2 in SPF, 80% mortality was recorded, whereas at 60% RH insect mortality reached almost 60%. The survival time (LT50) for S. carpocapsae applied in water was 36 h at 80% RH and only 3 h at 60% RH. With SPF the LT50 was prolonged to 58 h at 80% RH and >20 h at 60% RH. The addition of fumed silica, cross-linked sodium polyacrylate or alginate gel did not significantly improve DJ survival compared to SPF alone. Nematode caused mortality decreased when DBM larvae were added 9 h after DJ application. As 98% of the nematodes were still alive after 9 h, the nematodes must have lost efficacy. No significant increase in DBM morality was recorded when insects were exposed to DJs for 1, 4 or 20 h. The results indicate that host penetration on the leaf occurs within the first hour after application. Thus, the major advantage using the formulation is not to enhance nematode survival but rather to provide optimal environmental conditions that support nematode invasion of the host on foliage.

Four trials employing 1-m2 plots were conducted between November 2002 and April 2003 in Madera County, California, to evaluate the ability of two species of nematodes, Steinernema carpocapsae and Steinernema feltiae, to control navel orangeworm, Amyelois transitella, in infested pistachios on the ground. The plots were located in two 16.2 ha blocks of pistachio trees planted in sandy loam soil. A total of 4300 larvae were recovered from 17,593 laboratory-infested pistachios (24.4% average infestation). Nematodes were applied with a backpack sprayer at concentrations ranging from 50,000–1,000,000 infective juveniles (IJs)/m2 (100,000 IJs/m2 was assessed in all four trials) and an application rate of 374 or 500 ml/m2 water. S. carpocapsae was more effective than S. feltiae in pistachios and produced >72% mortality at a concentration of 100,000 IJs/m2 when nighttime temperatures were above freezing. S. carpocapsae was equally effective in bare and leaf-covered plots and persisted longer in sandier soil (8 weeks) than S. feltiae. S. carpocapsae has the potential to multiply in the field; 51.3% of the cadavers examined 21 days after application contained developing nematodes (n=226). Our trials demonstrated that S. carpocapsae can play a role in the post harvest control of navel orangeworm and that the formulation tested produced greater mortality than the formulations of S. feltiae tested at the same concentration.

During passage through the different components of a spray application system, a nematode suspension will undergo pressure changes. The extent of damage to three species of entomopathogenic nematodes (EPNs) (Steinernema carpocapsae, Heterorhabditis bacteriophora, and Heterorhabditis megidis) in suspension due to the effects of a pressure differential was studied. A French pressure cell and press was used to subject the newly emerged EPN suspensions to a series of pressure differentials ranging from 1283 kPa (186 psi) to 10,690 kPa (1550 psi). Aged suspensions (3 weeks) of H. bacteriophora and H. megidis were also evaluated. Damage was quantified by counting living and dead (whole and pieces) EPNs and by bioassay techniques. As the pressure differential increased, the relative viability of the EPNs decreased. Entomopathogenic nematodes that survived the pressure differential were, in general, able to survive for at least 1 week and maintain infectivity to Galleria mellonella at rates equivalent to EPNs that had not been pressure treated. In general, the relative viabilities of fresh and aged EPNs were equivalent after pressure differential treatments. The relative viability of the treated EPNs remained above 85% for pressure differentials less than or equal to 1283 kPa for H. megidis and 2138 kPa (310 psi) for S. carpocapsae and H. bacteriophora, but decreased rapidly for higher pressure differentials. Greater reductions in relative viability were experienced by Heterorhabditis spp. than S. carpocapsae, indicating that nematode species is an important factor to consider when defining spray operating conditions. We recommend a maximum operating pressure of 1380 kPa (200 psi) for H. megidis and 2000 kPa (290 psi) for S. carpocapsae and H. bacteriophora.

1. Entomopathogenic nematodes penetrate and kill Galleria mellonella within 48 h at optimal temperatures. 2. Low temperature induces infection latency, preventing host death until optimal conditions resume. 3. Infected Galleria survived 25 days at 5°C. On transfer to 25°C, 100% and 12.5% of Steinernema carpocapsae and Steinernema riobravis infected larvae died within 72 h. 4. Infective juvenile penetration decreased with decreasing temperature; declining from 49.7 and 49.3 nematodes/host at 25°C to 6.3 and 0.25 nematodes/host at 5°C for S. carpocapsae and S. riobravis , respectively. 5. Latent infection occurs, albeit infrequently, due to low host penetration at low temperature.

The quality of the most widely commercialized entomopathogenic nematodes, Steinernema carpocapsae (Weiser) and Heterorhabditis bacteriophora Poinar, was assessed from 30 shipments from six United States suppliers mailed to three locations. These suppliers comprise a cottage industry aimed in large part at a mail-order market. Most companies were accessible and reliably shipped pure populations of the correct species on time, in sturdy containers, and often with superb accompanying instructions. Nematodes were received in satisfactory condition with acceptable levels of viability. Consistency, however, was a problem, with each supplier having one or more weak spots to bolster. Most shipments did not contain the expected nematode quantity, and one shipment had no nematodes. Pathogenicity of several products against Galleria mellonella (L.) larvae was not equivalent to our controls. H. bacteriophora was not always available when ordered. A few products contained mixed populations of both nematode species. Application rate recommendations provided by some suppliers appeared unsound. We conclude that (1) the entomopathogenic nematode cottage industry lacks rigorous quality control, (2) self-regulation is problematic without feedback on quality, and (3) consumers are rarely able to provide this feedback. Improved reliability by the nematode industry will most likely be achieved via industry-generated agreement on standards for quality.

The aim of the present work was to investigate the efficacy of different spray methods (standard fan and full cone hydraulic nozzles and a spinning disc) for the application of infective juveniles (IJs) of Steinernema carpocapsae against insect pests on foliage. Larvae of Plutella xylostella on Chinese cabbage were used as a model system. The higher output hydraulic nozzles deposited the greatest number of IJs onto leaves and gave the greatest insect mortality (up to 98%). However, the spinning disc gave nearly 50% mortality while applying less than 9% of the Us compared with the most effective of the hydraulic nozzles. This suggests that further work on low volume (spinning disc) systems is justified and may lead to cost-effective applications of nematodes. The present work is discussed in relation to the timing of foliar applications and the effects of various abiotic and biotic factors.

Leptinotarsa decemlineata is less susceptible to entompathogenic nematodes than many other insect species. The roles of host-finding ability by the nematode Steinernema carpocapsae and host nonself response (immunity) toward the nematodes were determined to partially explain this low susceptibility. An agar-based assay was used to assess the chemotactic responses of S. carpocapsae infective juveniles to host-derived cues. The nematodes were attracted to CO 2 and feces of Galleria mellonella and Tenebrio molitor but were repelled by L. decemlineata feces. Examination of L. decemlineata larvae that survived exposure to S. carpocapsae revealed that the nematodes were often enclosed in hemocytic capsules in the hemocoel. When nematodes were injected directly into the hemocoel, an individual L. decemlineata larva could encapsulate up to 21 nematodes, but at loads above nine nematodes per larva at least one always escaped encapsulation resulting in insect death. Thus, the low susceptibility of L. decemlineata to S. carpocapsae is attributed, in part, to repellence of the host feces and to hemocytic encapsulation of penetrating nematodes. This paper adds to the understanding of the interactions between entomopathogenic nematodes and their insect hosts. This understanding is critical for the effective use of these pathogens as biological control agents.

To study the suppression of the prophenoloxidase cascade in the larval haemolymph of the turnip moth, Agrotis segetum by Steinernema carpocapsae and its symbiotic bacterium Xenorhabdus nematophilus , living S. carpocapsae , heat-killed S. carpocapsae , living X. nematophilus , and heat-killed X. nematophilus were injected in four different treatments into final-instar larvae of A. segetum . In all of the treatments, the activation of prophenoloxidase cascade (initiated by laminarin in the insect haemolymph which was drawn 1 h after injection) was inhibited. This inhibition occurred in a dose-dependent manner. On the other hand, injection of non-pathogenic and fungus-feeding nematodes, Aphelenchus avenae did not induce a similar inhibition, and the nematodes were found to be entrapped in nodules within a melanized sheath. Co-injection of Aph. avenae with S. carpocapsae or X. nematophilus suppressed the prophenoloxidase cascade, while Aph. avenae survived in the haemolymph without being trapped by haemocytes. In all haemolymph of larvae into which foreign-bodies were injected, the levels of prophenoloxidase were essentially the same as those from control larvae, when determined by α-chymotrypsin treatment. These results indicate that S. carpocapsae and/or X. nematophilus suppress the prophenoloxidase cascade at an early step and also interfere with the role of haemocytes in self-defence.

Infective juveniles of the entomopathogenic nematodes Steinernema carpocapsae (All and Mexican strains) and Heterorhabditis bacteriophora (HB1 and NC1 strains) are ensheathed in a cuticle retained from the previous molt. Exsheathment marks the transition from the free-living to the parasitic life cycle. Chemical and non-chemical exsheathment methods were examined. S. carpocapsae exsheaths more readily than H. bacteriophora. Movement on a substrate increased exsheathment in S. carpocapsae but had no effect on H. bacteriophora. Exposure to 1% sodium hypochlorite for 5 min resulted in nearly 100% sheath removal in both species. Storage increased exsheathment, with greater than 70% exsheathed in both species after 64 days at 7°C. Agitation and carbon dioxide did not stimulate exsheathment. Temperature alone did not stimulate exsheathment, however, increased temperatures accelerated exsheathment during storage. The availability of reliable exsheathment methods will enable analysis of exsheathment behavior and clarification of the role of the sheath in entomopathogenic nematodes.

A strain of Steinernema carpocapsae (G-13) selectively bred for improved host-finding was compared against two wild-type strains, the commercially available All strain and the Foundation strain from which the G-13 strain was derived, for changes in fitness. Selection did not affect pathogenicity, mobility, sex ratio, or morphology. However, the G-13 strain showed a gain of fitness with regard to host penetration and reproductive potential and a loss of fitness for storage stability. Acquiring enhanced host-finding abilities does not appear to be correlated with a serious reduction in overall fitness, and the potential of the selected G-13 strain for inundative biological control appears unlikely to be impaired. The possible significance of the three correlated responses to selection are discussed.