Production Of Infective Juveniles Research Articles

Virulence and Reproduction of Entomopathogenic Nematodes Isolated from a Single Mexican Locality

Abstract Entomopathogenic nematodes (EPNs) are important biological control agents of insect pests. Strains or isolates obtained in specific regions and utilized in situ might contribute to the success of EPNs, since they are adapted to local abiotic conditions. We isolated and identified three isolates each of Heterorhabditis bacteriophora Poinar and Steinernema carpocapsae (Weiser) from soils at Saltillo, Coahuila State, Mexico. These six isolates were bioassayed against larvae of Tenebrio molitor L., using six concentrations of infective juveniles (IJs) per larva (0, 10, 25, 50, 100, 200). EPN-induced mortality of the isolates ranged from 15.2% to 100%. The designated M5 isolate of S. carpocapsae caused 100% mortality after 72 h at concentrations ≥25 IJs/larva with a median lethal concentration of 4.99 IJs/larva. Comparison of mortality levels induced at the same concentration of the six EPN isolates indicated that the Steinernema isolates, in general, induced higher mortality levels than the Heterorhabditis isolates. IJ production in T. molitor larvae also was greatest with the M5 isolate of S. carpocapsae following exposure of larvae to a concentration of 100 IJs/larva with a mean of 17,320 IJs/larva. Based on induced mortality and IJ production, the S. carpocapsae M5 isolate appears to be a viable candidate for further study and possible development for use in insect pest management programs. This study indicates that naturally coexisting local nematode isolates possess different attributes critical for their use as biocontrol agents.

Biocontrol potential of native entomopathogenic nematodes against coconut rhinoceros beetle, Oryctes rhinoceros (L.) (Coleoptera: Scarabaeidae) under laboratory conditions

BackgroundIndia is the world's leading producer of coconuts. Many biotic and abiotic constrains limit global palm yield and among the biotic factors, the coconut rhinoceros beetle, Oryctes rhinoceros (L.) (Coleoptera: Scarabaeidae) is the major problem in India. The adult beetle attacks the unopened leaves and inflorescences, resulting in a yield loss of more than 10%. O. rhinoceros grubs and adults have different feeding habits as the adults feed on plant tissues, whereas the grubs primarily feed on rotting organic matter. Non-feeding stage, i.e. the larval stage, which is cryptic in nature and spends nearly 90–160 days in the breeding site, is amenable to any control measures so as to reduce the population of actual damaging adult stage. However, indiscriminate use of chemical insecticides has created a lot of environmental and regulatory issues, thus warranting an ecologically safe and environmental friendly alternative option. Hence, indigenous entomopathogenic nematode (EPN) strains, viz. Heterorhabditis indica (CPCRI-Hi1), Steinernema abbasi (CPCRI-Sa1), and S. carpocapsae (CPCRI-Sc1), virulence and reproductive capacity were evaluated against second instar larvae of O. rhinoceros.ResultsOryctes rhinoceros larval susceptibility to EPN significantly varied with the treatment dose and period of exposure. The highest larval mortality was observed with S. carpocapsae (100%), and S. abbasi (92%) at 10 days post treatment, whereas H. indica strain induced 72% mortality. At 72 h of incubation, the LC50 values of Sc1, Sa1 and Hi1 strains were 1078, 1663 and 9780 IJs larva−1, respectively. With different concentration of EPN tested, the production of infective juveniles (IJs) inside the cadavers for Sc1, Sa1 and Hi1 varied between 3223–10,365; 4722–96,572 and 3483–85,453 larvae−1, respectively.ConclusionBased on the virulence, reproductive capacity, searching ability and LC50 values, it is suggested that strain Sc1 have great potential as a biocontrol agent for the Oryctes management in coconut palms under humid tropical ecosystem. Present study found the effective native strain against O. rhinoceros, and its field efficacy should be tested further to include the EPNs in the integrated pest management program in coconut.

Entomopathogenic nematodes (Heterorhabditidae and Steinernematidae), to control Triatoma infestans populations (Hemiptera: Reduviidae), Chagas disease vector

Pyrethroid insecticides are the only strategy to control Triatoma infestans populations (Hemiptera: Reduviidae), the main vector of Chagas disease in Argentina. However, toxicity effects and resistance have resulted from repeated applications of these insecticides over long periods. The aim of this study was to evaluate the efficacy of three isolates of entomopathogenic nematodes (EPN): Heterorhabditis bacteriophora (RN and SUP strains) and Steinernema feltiae (NEMAPOM), against pyrethroid-resistant and non-resistant T. infestans populations. Survival of pyrethroid-resistant and non-resistant T. infestans nymphs was significantly reduced in those parasitized by EPN strains compared to the controls, reaching values close to 10%, three and six days after exposure to Heterorhabditis and Steinernema, respectively. The lowest survival of T. infestans nymphs resulted from application of H. bacteriophora strains. No significant differences were observed between pyrethroid-resistant and non-resistant T. infestans populations for any of the parameters evaluated. The three strains were able to multiply and emerge as infective juveniles (IJs) from T. infestans cadavers, completing their lifecycle in both pyrethroid-resistant and non-resistant populations, but highest IJ production was observed in H. bacteriophora strains. Future studies should consider the incorporation of drought-tolerant EPN strains, as well as evaluating an adequate release strategy before field implementation of EPNs as biological control agents of T. infestans.

In vivo production of entomopathogenic nematodes suppressed by asymptomatic bacterial contaminants

Summary Entomopathogenic nematodes (EPN) are excellent biological control agents possessing recycling ability as one of their major attributes. We report the presence of asymptomatic bacteria that can lead to disrupted or low progeny production in Heterorhabditis indica. In a one-to-one in vitro competitive bioassay with contaminants associated with H. indica cuticle, there was a significant suppression in the growth of Sphingomonas koreensis when stressed with the nematode symbiont Photorhabdus luminescens; however, P. luminescens was suppressed when sandwiched between Ochrobactrum anthropi. Bacillus bombysepticus associated with laboratory-reared Galleria when stressed by P. luminescens was significantly suppressed, but not so in the reverse assay. Both O. anthropi and B. bombysepticus were found to be insecticidal to Galleria larvae when fed orally. Tripartite interactive studies on the growth and multiplication of H. indica-P. luminescens symbionts in Galleria larvae, predisposed to S. koreensis, revealed no significant difference initially in the hermaphrodite formation, but subsequently there was a significant decline in the formation of amphimictic females and the final production of infective juveniles. In in vitro studies, none of the contaminants supported the growth and development of axenic H. indica. Adequate precautions should be taken to maintain proper hygiene to eliminate such contaminants while culturing the Galleria and EPN for use in the biological control of insects.

Virulence of entomopathogenic nematodes against castor capsule borer Conogethes punctiferalis (Guenée)

Two EPN species, Heterorhabditis indica Poinar and H. bacteriophora Poinar were evaluated for their virulence and reproductive potential against late instar larvae of castor capsule borer Conogethes punctiferalis (Guenee) with wax moth Galleria mellonella (L.) used for comparison. Late instar larvae were found highly susceptible at all six infective juvenile (IJ) concentrations (30, 60, 90, 120, 150 and 200 IJ larva−1) of both the EPNs evaluated. At 48 hr post infection, complete larval mortality was observed in both capsule borer and wax moth. LC50 values of 570 and 40.1 IJ larva−1 for capsule borer and 15.1 and 5.4 IJ larva−1 forwax moth were observed with H. bacteriophora and H. indica, respectively at 24 hr exposure. These values indicated the highly virulent nature of the EPNs. In capsule borer, maximum IJ production/cadaver for H. bacteriophora and H. indica was 84 ± 4.6 x 103 IJs larva−1 and 98 ± 6.7 x 103 IJs larva−1 at an inoculation concentration of 30 IJs larva−1. In wax moth, it was 262.3 ± 27.2 x 103 IJs larva−1 and 231.9 ± 8.1 x 103 IJs larva−1 for H. bacteriophora and H. indica, at an inoculation concentration of 90 IJs larva−1. These results reveal that host size is very important in fixing optimal inoculation concentration and final IJ production, and that both the EPNs have good potential for the management of capsule borer in castor.

Compatibility between entomopathogenic nematodes and crop protection products used in maize seed treatment

Chemical insecticides are widely used to control soil pests but not always effective. Entomopathogenic nematodes (NEPs) are found in the soil and depend on host insects to complete their life cycle, and therefore have the potential to control soil pests. Thus, we aimed to investigate the possible joint use of these control methods by assessing the compatibility of two nematodes (Heterorhabditis amazonensis GL and Heterorhabditis amazonensis MC01) with five crop protection products used for maize seed treatment (Maxim®, Cruiser 350 FS®, Fortenza 600 FS®, Avicta 500 FS®, and Amulet®), as well as one neem-based product (NeenMax®). The experimental design was completely randomized with five replicates, six treatments, and one control, in which only distilled water was added to nematode suspension. Each replicate consisted of a test tube containing 1 mL suspension with 2,000 infective juveniles (IJs) and 1 mL of diluted product, following the manufacturer's recommendation. The evaluated parameters were viability, infectivity on Tenebrio molitor larvae and IJs production after exposure to products. Both nematodes were compatible with NeenMax® and Fortenza 600 FS® since they did not differ from the control and were classified as innocuous. Cruiser 350 FS ® was also compatible with the nematodes since the effect value of the product was lower than 30%. Amulet® was classified as slightly noxious, reducing H. amazonensis MC01 and H. amazonensis GL infectivity by 17.5% and 28.5%, and production by 18.2% and 22.3%, respectively. Despite not having reduced viability, Avicta 500 FS® and Maxim® were considered harmful. This is because Avicta 500 FS® and Maxim® reduced productivity by 70.0% and 72.5% and production by 66.1% and 65.4% for H. amazonensis MC01, respectively. For H. amazonensis MC01, both Avicta 500 FS® and Maxim® reduced infectivity by 76.19%, and production by 63.7% and 62.3%, respectively.

In vitro production of the biological control agent Heterorhabditis indica SL0708 in different agar media

ABSTRACTHeterorhabditis indica SL0708 is an entomopathogenic nematode isolated from Valle del Cauca-Colombia, whose bacterial symbiont, Photorhabdus luminescens subsp. akhurstii SL0708, has potential to control pests of economic importance in Colombia. Since in vivo production does not supply its demand, this investigation evaluated H. indica SL0708 production on different agar media. Five culture media (I, II, III, IV and V) were evaluated for productivity and pathogenicity of infective juveniles (IJs). IJs emerged between 11 and 16 days after inoculation in all media, with a total of 2.7 × 104 and 4.7 × 106 IJs produced during 15 days after IJs emergence, with maximum productivity at day five and high variability. Pathogenicity to Galleria mellonella larvae was not significantly different between in vitro and in vivo produced IJs on all media tested. Media IV and V were selected for their higher productivity. Subsequently, nematode inoculum size was evaluated in selected media at 2000, 4000 and 6000 IJs ml−1, but significant differences were not observed in productivity and pathogenicity. Lastly, lipid source influence was evaluated in medium IV comparing canola, olive and soy oils. None of the plant-based oils had a significant effect on IJs production and pathogenicity. A medium was selected for H. indica SL0708 IJs production which was suitable in terms of productivity, culture time and pathogenicity of IJs produced. The medium and parameters selected in this study could be applied as an alternative for mass production of this entomopathogenic nematodes.

FACTORS AFFECTING PROPAGATION OF HETERORHABDITTIS BACTERIOPHORA POINAR, AN ENTOMOPATHOGENIC NEMATODE IN PLUTELLA XYLOSTELLA (L.)

Entotomopathogenic nematode, Heterorhabittis bacteriophora possess tremendous potential for biological control of Plutella xylostella (L.) commonly known as the diamond back moth (DBM), major pest of cabbage and cauliflower. Five parameters viz., incubation dose, host body weight, incubation temperature, host food plant and host feeding status were taken to determine their effect on the propagation of H. bacteriophora in final instar of P. xylostella. The number of infective juveniles (IJs) produced increased with the increase in the inoculation dose up to 15 (IJs) per larva. Further increase in dose adversely affected the nematode progeny production because of overcrowding. A positive correlation between host body weight and number of IJs/mg body weight was observed (r=0.8343). Optima temperature for H. bacteriophora was found to be 25oC and the range was 15oC to 35oC. There was no significant difference in nematode progeny production and host food plant viz., cabbage, cauliflower, knolknol and mustard. Similarly IJs production per mg body weight was not significantly different in starved and fed larvae (host feeding status).

Initial Fungal Infection Reduce the Penetration and Reproduction Rate of Steinernema riobravae in Galleria mellonella

This study was carried out to investigate the virulence of both entomopathogenic nematode Steinernema riobravae and entomopathogenic fungi Beauveria bassiana against last larval instars of Galleria mellonella. Both pathogens were either applied individually and as a group by inoculation of nematode simultaneously or 2, 4 and 6 days post fungal infection. Moreover, the effect of fungal infection on the nematode’s penetration ability and reproduction potential were also evaluated. The results indicated that by increasing pathogen concentrations the host mortality percentage increased. LC50 values were 12.3 IJs/ larva for S. riobravae and 309.62conidia/ml for B. bassiana. The nematode’s penetration ability was significantly reduced when nematode applied at 2, 4, and 6 days post fungal infection. A significant reduction in infective juveniles production was observed when nematode applied at 2 and 6 days post fungal infection. However, the combination of two pathogens increased the effectiveness of pest control, their development is affected possibly by competition for the host and the understanding of these interactions will make it possible to determine the compatibility of the components of biological control to be used.

Comparative efficacy of indigenous heterorhabditid nematodes from north western Himalaya and Heterorhabditis indica (Poinar, Karunakar & David) against the larvae of Helicoverpa armigera (Hubner)

ABSTRACTThe efficacy of three Heterorhabditis spp of entomopathogenic nematodes (EPNs) from north western Himalaya, India was studied against the larvae of pod borer, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae), under the laboratory conditions. The larvae were exposed to 10, 20, 30 and 40 infective juveniles (IJs) of each nematode species for different time periods and they were found to be susceptible to all the EPNs tested. However, the susceptibility of larvae to nematode infection varied according to the concentrations of IJs and their exposure periods. The efficacy of these indigenous entomopathogenic nematodes was also compared against commercially available entomopathogenic nematode, H. indica. Appreciably good performance was achieved by H. bacteriophora (HRJ), which showed 73.3% mortality of insect larvae in 96 h exposure time against third instar larvae, while H. indica produced 80.0% mortality. However it was noticed that with the advancement of larval stage its mortality rate reduced and vice versa with the exposure period. All tested EPNs were also found to reproduce within the host and maximum production of IJs was recorded in H. bacteriophora (26.0 ± 3.76 × 103 IJs/larva) at the concentration of 40 IJs/larva.

Infection of Galleria mellonella larvae by Steinernema affine and production of infective juveniles

Infection of Galleria mellonella larvae by Steinernema affine and production of infective juveniles

THE CONTINUAL FORMING AND CONTRIBUTION OF INFECTIVE JUVENILES PRODUCED VIA ENDOTOKIA MATRICIDA OF ENTOMOPATHOGENIC NEMATODES IN THE FAMILY OF STEINERNEMATIDAE AND HETERORHABDITIDAE

The non-feeding developmentally arrested infective juveniles (IJs) of entomopathogenic nematodes in the family of Steinernematidae and Heterorhabditidae seek out a susceptible insect host and initiate infections. The aim of the research was to examine the continual<br />forming and contribution of IJs produced via endotokia matricida (IJs-EM) of Heterorhabditis bacteriophora, Steinernema glaseri, and S. carpocapsae. The research was conducted at the Laboratory of Nematology of the Saga University, Japan (April 2001-April<br />2002) and the Laboratory of Nematology of the Indonesian Legume and Tuber Crops Research Institute (June 2003-October 2004). The nematode progenies were investigated using the greater wax moth, Galleria mellonella, pre-inoculated with 50 IJs at 25°C.<br />Results showed that three reproductive adult generations were observed at day 18th. There were 135,000, 128,000 and 133,000 IJs per insect cadaver produced in H. bacteriophora, S. glaseri and S. carpocapsae, respectively. Endotokia matricida contributed a higher number of IJs than that of a normal mode of IJs production. The ratios are 81%, 28% and 64% for H. bacteriophora, S. glaseri, and S. carpocapsae of the IJs total production, respectively. Among the generations, the highest contribution of IJs was come from the<br />third adult generation bearing endotokia matricida, i.e., 63%, 24% and 51% for the three nematode species. Although the IJs-EM were more transparent compared to the normal IJs, they were morphologically similar. The results show that endotokia matricida has a pivotal role in a species maintenance and survival strategy of entomopathogenic nematodes in extreme environmental conditions.

THE CONTINUAL FORMING AND CONTRIBUTION OF INFECTIVE JUVENILES PRODUCED VIA ENDOTOKIA MATRICIDA OF ENTOMOPATHOGENIC NEMATODES IN THE FAMILY OF STEINERNEMATIDAE AND HETERORHABDITIDAE

The non-feeding developmentally arrested infective juveniles (IJs) of entomopathogenic nematodes in the family of Steinernematidae and Heterorhabditidae seek out a susceptible insect host and initiate infections. The aim of the research was to examine the continual<br />forming and contribution of IJs produced via endotokia matricida (IJs-EM) of Heterorhabditis bacteriophora, Steinernema glaseri, and S. carpocapsae. The research was conducted at the Laboratory of Nematology of the Saga University, Japan (April 2001-April<br />2002) and the Laboratory of Nematology of the Indonesian Legume and Tuber Crops Research Institute (June 2003-October 2004). The nematode progenies were investigated using the greater wax moth, Galleria mellonella, pre-inoculated with 50 IJs at 25°C.<br />Results showed that three reproductive adult generations were observed at day 18th. There were 135,000, 128,000 and 133,000 IJs per insect cadaver produced in H. bacteriophora, S. glaseri and S. carpocapsae, respectively. Endotokia matricida contributed a higher number of IJs than that of a normal mode of IJs production. The ratios are 81%, 28% and 64% for H. bacteriophora, S. glaseri, and S. carpocapsae of the IJs total production, respectively. Among the generations, the highest contribution of IJs was come from the<br />third adult generation bearing endotokia matricida, i.e., 63%, 24% and 51% for the three nematode species. Although the IJs-EM were more transparent compared to the normal IJs, they were morphologically similar. The results show that endotokia matricida has a pivotal role in a species maintenance and survival strategy of entomopathogenic nematodes in extreme environmental conditions.

Mortality and nematode production in Spodoptera littoralis larvae in relation to dual infection with Steinernema riobrave, Heterorhabditis bacteriophora, and Beauveria bassiana, and the host plant

The present study aimed to evaluate the interactive applications of the promising biocontrol agents, the entomopathogenic nematodes (EPNs) Steinernema riobrave and Heterorhabditis bacteriophora and the entomopathogenic fungus (EPF) Beauveria bassiana, each at the LC25 level, to the last instars of the Egyptian cotton leafworm, Spodoptera littoralis, in either sequential or simultaneous fashion to determine whether interactions (synergistic, additive, or antagonistic) among these entomopathogens were present. Moreover, the indirect impact of two cultivated host plants (cabbage and cowpea) and three wild host plants (castor, Jew’s mallow, and mallow) or their primary metabolites (total protein, carbohydrate, and lipid content) on the virulence of these entomopathogens and on nematode production also was assessed. Synergisms were observed among the different entomopathogen pairings. In case where sequential applications were made, applying the EPF first was best for infective juvenile (IJ) production; applying the EPN prior the EPF significantly reduced IJ production. Larvae raised on cabbage (the most lipid–rich diet) were most resistant for both EPN species tested. In general, not many IJs were produced from hosts that fed on mallow, but many were produced from hosts that fed on castor. In the case of EPF, B. bassiana was most effective at controlling larvae that fed on mallow, which was considered the least nutritive of the host plants. The results obtained are suggestive of an efficient control to S. littoralis. This would be achieved through the implementation of an integrated program including combining the entomopathogens studied with each other, or intercropping castor (in the case of the nematode application), or mallow (in the case of the fungus application) with cotton for enhancing the control of this insect pest in Egypt.

Biochemical effects of Steinernema feltiae, Steinernema riobrave and Heterorhabditis bacteriophora on Spodoptera littoralis larvae

Article History In the present study, the infectivity of the three entomopathegnic nematodes, Steinernema feltiae, Steinernema riobrave and Heterorhabditis bacteriophora, on the cotton leafworm, Spodoptera littoralis was studied. Moreover, the effect of these pathogens on certain biochemical and physiological aspects of the host was also studied. H. bacteriophora, appeared to be more pathogenic than S. riobrave and S. feltiae to the S. littoralis larvae. The highest production (7000 infective juveniles) was obtained, where infective juvenile production from cadavers infected with H. bacteriophora was higher than that produced from cadavers infected with S. riobrave and S. feltiae. The principle nutrients (total protein, carbohydrate and lipid) of the host larvae were highly decreased post-infection with the nematodes S. riobrave and H. bacteriophora. The activity of some larval enzymes was also affected due to infection by these nematodes. Thus, the activity of carbohydrate hydrolyzing enzymes (amylase, invertase and trehalose) changed depending on the species of the pathogen and the enzyme. Amylase activity decreased with the infection by H. bacteriophora, and the reverse was obtained with the infection by S. riobrave and S. feltiae where such activity increased. Invertase and Trehalase activity increased with the infection by three nematode species. The highest increase was obtained in case of infection by S. riobrave. Activities of acid and alkaline phosphatases increased due to infection by S. riobrave, H. bacteriophora. The only exception was a non-significant decrease in the alkaline phosphatase activities of larvae infected with S. feltiae. Whereas, the activity of transaminases (GOT and GPT) was highly decreased with the infection by H. bacteriophora and S. riobrave.

Susceptibility of Spodoptera frugiperda and Helicoverpa gelotopoeon (Lepidoptera: Noctuidae) to the entomopathogenicnematode Steinernema diaprepesi (Rhabditida: Steinernematidae)under laboratory conditions

Spodoptera frugiperda Smith and Helicoverpa gelotopoeon (Dyar) are important agricultural pests of several crops. The aim of the present work was to evaluate the susceptibility of larvae of both insects to an isolate of Steinernema diaprepesi Nguyen & Duncan under laboratory conditions, as well as the capacity of the nematode to multiply on these lepidoterans. Larvae (n = 15) were exposed to 0 (control), 50, and 100 infective juveniles (IJs) per Petri dish. Mortality was evaluated every 24 h during 6 d, and emerging IJs were counted. Mortality of S. frugiperda was 93% and 100% with 50 and 100 IJs dosage, and 87% and 93% in H. gelotopoeon, respectively. The production of IJs was significantly different between doses (P ≤ 005) for S. frugiperda (11 329 with 50 IJs vs. 27 155 with 100 IJs) but not for H. gelotopoeon (19 830 vs. 26 361, respectively). This is the first study evaluating the susceptibility of these lepidopterans to S. diaprepesi. These results encourage the possibility of using this nematode for biological control of both pests.

Desiccation and cold storage of Galleria mellonella cadavers and effects on in vivo production of Steinernema carpocapsae

Direct application of insect cadavers infected with entomopathogenic nematodes (EPN) can successfully control target pest insects. Little is known about the effects of environmental factors (desiccation and temperature) on the production process for infective juveniles (IJ) in insects. We examined the effects of desiccation time and cold storage (6.7 °C) on IJ production of the nematode Steinernema carpocapsae in Galleria mellonella cadavers at 30.8 and 57% humidity. Under desiccation, the IJ yield in cadavers increased gradually and reached a maximum on day 5. IJ yield gradually declined from day 6 onwards and was almost zero by day 15. In general, cold storage at 6.7 °C caused negative effects on IJ production in desiccated cadavers. Approximately 56 h post infection was the time at which nematodes were most sensitive to low temperatures during development in cadavers. Five-day desiccated cadavers generated higher mortality and more rapid death of Galleria mellonella larvae than using newly (day 0) desiccated cadavers. This study describe methods of optimizing rearing techniques such as desiccation and cold storage to promote the mass production and application of EPN- infected host cadavers for the field control of insect pests.

EFFICACY OF EGYPTIAN (BA1) AND GERMAN (HB1-3) STRAINS OF ENTOMOPATHOGENIC NEMATODE, HETERORHABDITIS BACTERIOPHORA, AGAINST GALLERIA MELLONELLA L.

Studies were carried out to find out the efficacy of Egyptian strain (BA1) and exotic European strain (Hb1-3) of entomopathogenic nematode; Heterorhabditis bacteriophora against full-grown larva of Galleria mellonella L. Infection took place in plastic cups (100 cc) half-filled with moistened sterilized sandy soil that treated with 5 concentrations of each of the two strains of nematode; 5, 10, 20, 40 and 80 infective juveniles (IJs)/cup. Two densities of Galleria (1 and 5 larvae/cup) were used for each strain at each concentration. It was found that the efficacy of entomopathogenic nematode strains, on the full-grown larvae of G. mellonella was concentration dependent; i.e. the mortality percentage increased as the IJs concentrations were increased. Individual treatment (one larva/cup) led to more efficacy than using 5/cup at 25°C. The production of infective juveniles from G. mellonella larvae infected at concentrations of 1, 2, 4, 8 and 16 IJs/cup was, generally, higher in BA1 strain compared to Hb1-3 strain. The histopathological observations revealed variable effects on G. mellonellalarvae after infection with the entomopathogenic nematode. Muscles suffered destruction in the fibrillate with some fragments and fat body tissues showed high vacuolation.

Efficacy of indigenous entomopathogenic nematodes from Meghalaya, India against the larvae of taro leaf beetle, Aplosonyx chalybaeus (Hope).

The efficacy of three entomopathogenic nematode (EPN) species, Heterorhabditis indica, Steinernema thermophilum, and S. glaseri, from Meghalaya, India was studied against the larvae of taro leaf beetle, Aplosonyx chalybaeus (Hope) (Coleoptera: Chrysomelidae), under the laboratory conditions. The beetle larvae (grubs) were exposed to 25, 50, 75, 100 and 200 infective juveniles (IJs) of each nematode species for different time periods and they were found to be susceptible to all the EPNs tested. However, the susceptibility of grubs to nematode infection varied according to the dosages of IJs and their exposure periods. Appreciably good performance was achieved by S. glaseri, which showed 100% mortality of insect larvae in 48h exposure time. At 48h of incubation, its LC50 value was 90.3 IJs/larva, which was lower than that of S. thermophilum (115.0 IJs/larva) and H. indica (186.0 IJs/larva), at the same exposure time. All the tested nematode species were also found to reproduce within the host and produced infective juveniles. H. indica, however, showed comparatively more production of IJs per cadaver of infected host (168.9×10(3) IJs/larva), as compared to the other two tested nematode species. The production of IJs per cadaver of infected host by S. thermophilum was recorded to be 82.0×10(3) IJs/larva. In case of S. glaseri, while production of IJs increased initially to 18.9×10(3) IJs/larva at concentration of 100 IJs/larva, it declined thereafter to 14.7×10(3) IJs/larva at the dose of 200 IJs/larva. In conclusion, the evidence obtained in this study suggests that all the three indigenous EPN species are virulent enough to produce 100% mortality in the last instar larvae of A. chalybaeus. These EPN species thus have potential scope for the management of A. chalybaeus in taro crops.

Effect of insect cadaver desiccation and soil water potential during rehydration on entomopathogenic nematode (Rhabditida: Steinernematidae and Heterorhabditidae) production and virulence

We examined the influence of insect cadaver desiccation on the virulence and production of entomopathogenic nematodes (EPNs), common natural enemies of many soil-dwelling insects. EPNs are often used in biological control, and we investigated the feasibility of applying EPNs within desiccated insect cadavers. Desiccation studies were conducted using the factitious host, Galleria mellonella (Lepidoptera: Pyralidae, wax moth larvae) and three EPN species ( Heterorhabditis bacteriophora ‘HB1’, Steinernema carpocapsae ‘All’, and Steinernema riobrave). Weights of individual insect cadavers were tracked daily during the desiccation process, and cohorts were placed into emergence traps when average mass losses reached 50%, 60%, and 70% levels. We tracked the proportion of insect cadavers producing infective juveniles (IJs), the number and virulence of IJs produced from desiccated insect cadavers, and the influence of soil water potentials on IJ production of desiccated insect cadavers. We observed apparent differences in the desiccation rate of the insect cadavers among the three species, as well as apparent differences among the three species in both the proportion of insect cadavers producing IJs and IJ production per insect cadaver. Exposure of desiccated insect cadavers to water potentials greater than −2.75 kPa stimulated IJ emergence. Among the nematode species examined, H. bacteriophora exhibited lower proportions of desiccated insect cadavers producing IJs than the other two species. Desiccation significantly reduced the number of IJs produced from insect cadavers. At the 60% mass loss level, however, desiccated insect cadavers from each of the three species successfully produced IJs when exposed to moist sand, suggesting that insect cadaver desiccation may be a useful approach for biological control of soil insect pests.