Species Heterorhabditis Bacteriophora Research Articles

PATHOGENICITY, PROGENY PRODUCTION AND HISTOPATHOLOGICAL EFFECTS OF THREE ENTOMOPATHOGENIC NEMATODES IN THE GREATER WAX MOTH, GALLERIA MELLONELLA (L.)

Entomopathogenic nematodes (EPNs) of the genera Steinernema and are associated with bacterial symbionts of the genus Xenorhabdus and Photorhabdus, respectively. They are being produced commercially and used as biological control agents against many soil insect pests. The present study was carried out to investigate the effectiveness of entomopathogenic nematode species Heterorhabditis bacteriophora, Steinernema carpocapsae and Steinernema riobravis against the full-grown larvae of greater wax moth Galleria mellonella. It was found that the mortality percentage increased as the concentration of the infective juveniles (IJs) increased. Generally, H. bacteriophora was more effective than S. carpocapsae and S. riobravis. The production rate increased as the concentration of IJs increased. H. bacteriophora was the highest reproductive strain than S. carpocapsae and S. riobravis at the five tested concentrations. The three nematode species affected the muscles and fat tissues, where muscle fibers suffered destruction with some fragmentation, also complete destruction and disintegration of tissues was noticed in the treated G. mellonella larvae.

Comparison of indigenous and exotic entomopathogenic nematode strains for control of the cedar web-spinning sawfly, Cephalcia tannourinensis in vitro

Cedars of Lebanon Cedrus libani have been attacked since 1990s by a hymenopteran sawfly, Cephalcia tannourinensis (Chevin), causing considerable damage to the foliar buds. A biological control programme using entomopathogenic nematodes (EPNs) was conducted in vitro against C. tannourinensis prenymphs. Two EPNs strains belonging to the same species Heterorhabditis bacteriophora were used; one indigenous to the country (LIB04) and the other a commercial strain (HbCom). Four EPNs concentration rates (40, 100, 250, 480 infective juveniles) were tested against C. tannourinensis prenymphs. Higher mortality was noted for the indigenous strain, LIB04, independently from all concentrations (100%). Emergence of EPNs was observed following 12–17 days from the first contact between EPNs and C. tannourinensis prenymphs. This parameter indicated that EPNs succeeded to complete all their reproductive cycle inside the C. tannourinensis cadavers before emerging. Bioassays were realised in jars containing soil extracted from the forest in order to validate the scenario suggested for application in situ. Most C. tannourinensis prenymphs were attacked by the EPNs on the surface.

Susceptibility of Dalotia coriaria (Kraatz) (Coleoptera: Staphylinidae) to Entomopathogenic Nematodes (Rhabditida: Heterorhabditidae and Steinernematidae).

Dalotia coriaria (Kraatz) (Coleoptera: Staphylinidae) and entomopathogenic nematodes (Rhabditida: Heterorhabditidae and Steinernematidae) are two soil-dwelling biological control agents used to manage western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) and fungus gnats Bradysis spp. (Diptera: Sciaridae) in glasshouses. Growers often use multiple natural enemies to achieve economic control, but knowledge of interactions among natural enemies is lacking. We conducted a laboratory bioassay to test the pathogenicity of four commercially available nematode species—Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhbditidae), Steinernema carpocapsae (Weiser) (Rhabditida: Steinernematidae), S. feltiae (Filipjev), and S. riobrave Cabanillas et al.—to third instar and adult D. coriaria. Third instars were three times more susceptible than the adults to the entomopathogenic nematodes. Mortality for D. coriaria adults and third instars treated with S. feltiae and H. bacteriophora was lower than the mortality for D. coriaria adults and third instars treated with S. carpocapsae and S. riobrave. Neither infective juvenile foraging behavior nor size correlates with D. coriaria mortality. Dalotia coriaria appears to be most likely compatible with applications of S. feltiae and H. bacteriophora.

Efficacy of the entomopathogenic nematodes and their based-product on some species of mealybugs (Hemiptera: Pseudococcidae) in Egypt

The infectivity of three Egyptian Heterorhabditid nematode species Heterorhabditis bacteriophora (Poinar), Heterorhabditis indica (Poinar) and Heterorhabditis baujardi (Poinar) ( Rhabditida : Heterorhabdilidae) and one imported Steinernematid species, Steinernema abbasi (Elawad) (Rhabditida: Steinernematidea) were evaluated against preadult of the citrus mealybug Planococcus citri (Risso) (Hemiptera: Pseudococcidae) and adult of Egyptian mealybug Icerya aegyptiaca (Douglas) (Hemiptera: Monophlebidae) under laboratory conditions. Also, laboratory and semifield evaluation of the efficiency of entomopathogenic nematodes (EPN) alone or mixed with wax remover Oleyl-polypeptide, against adults and nymphs of the mealybug Ferrisia virgata (Cockerell) (Hemiptera: Pseudococcidae) were carried out. Nematode reproduction in their cadavers were detected. Moreover, the effect of Steinernema carpocapsae alone or with medical additive (Docusate Sodium) comparing with Super Misrona oil were studied on the grape mealybug, Planococcus ficus (Signoret) . Three methods of formulation of Egyptian entomopathogenic nematodes were tested for their effectiveness on H. bacteriophora and S. carpocapsae. These formulations are water-dispersible granules (WDG), Calcium alginate geland infected cadavers. The infectivity of the formulated nematodes was tested against I. aegyptiaca adults.

The first record of entomopathogenic nematodes (Rhabiditiae: Steinernematidae and Heterorhabditidae) in natural ecosystems in Lebanon: A biogeographic approach in the Mediterranean region

A survey of entomopathogenic nematodes in Lebanon was conducted for the first time during 2008–2009. Samples were collected on the coastal strip and in nine vegetation types extending from the coastal line to 3088 m above sea level. Wooded and herbaceous ecosystems were considered for sampling purposes. A total of 570 samples were taken, out of which 1% were positive for entomopathogenic nematodes. Approximately, 15.8% out of the 19 sites sampled revealed entomopathogenic nematodes presence (representing three samples). Two entomopathogenic nematodes species Heterorhabditis bacteriophora and Steinernema feltiae were recovered, and identification of their symbiotic bacteria revealed the presence of a Xenorhabdus bovienii, Photorhabdus temperata subsp. thracensis, Photorhabdus luminescens subsp. kayaii and Photorhabdus luminescens subsp. Laumondii.

Photorhabdus luminescens genes induced upon insect infection.

BackgroundPhotorhabdus luminescens is a Gram-negative luminescent enterobacterium and a symbiote to soil nematodes belonging to the species Heterorhabditis bacteriophora. P.luminescens is simultaneously highly pathogenic to insects. This bacterium exhibits a complex life cycle, including one symbiotic stage characterized by colonization of the upper nematode gut, and a pathogenic stage, characterized by release from the nematode into the hemocoel of insect larvae, resulting in rapid insect death caused by bacterial toxins. P. luminescens appears to sense and adapt to the novel host environment upon changing hosts, which facilitates the production of factors involved in survival within the host, host-killing, and -exploitation.ResultsA differential fluorescence induction (DFI) approach was applied to identify genes that are up-regulated in the bacterium after infection of the insect host Galleria mellonella. For this purpose, a P. luminescens promoter-trap library utilizing the mCherry fluorophore as a reporter was constructed, and approximately 13,000 clones were screened for fluorescence induction in the presence of a G. mellonella larvae homogenate. Since P. luminescens has a variety of regulators that potentially sense chemical molecules, like hormones, the screen for up-regulated genes or operons was performed in vitro, excluding physicochemical signals like oxygen, temperature or osmolarity as variables. Clones (18) were obtained exhibiting at least 2.5-fold induced fluorescence and regarded as specific responders to insect homogenate. In combination with a bioinformatics approach, sequence motifs were identified in these DNA-fragments that are similar to 29 different promoters within the P. luminescens genome. By cloning each of the predicted promoters upstream of the reporter gene, induction was verified for 27 promoters in vitro, and for 24 promoters in viable G. mellonella larvae. Among the validated promoters are some known to regulate the expression of toxin genes, including tccC1 (encoding an insecticidal toxin complex), and others encoding putative toxins. A comparably high number of metabolic genes or operons were observed to be induced upon infection; among these were eutABC, hutUH, and agaZSVCD, which encode proteins involved in ethanolamine, histidine and tagatose degradation, respectively. The results reflect rearrangements in metabolism and the use of other metabolites available from the insect. Furthermore, enhanced activity of promoters controlling the expression of genes encoding enzymes linked to antibiotic production and/or resistance was observed. Antibiotic production and resistance may influence competition with other bacteria, and thus might be important for a successful infection. Lastly, several genes of unknown function were identified that may represent novel pathogenicity factors.ConclusionWe show that a DFI screen is useful for identifying genes or operons induced by chemical stimuli, such as diluted insect homogenate. A bioinformatics comparison of motifs similar to known promoters is a powerful tool for identifying regulated genes or operons. We conclude that signals for the regulation of those genes or operons induced in P. luminescens upon insect infection may represent a wide variety of compounds that make up the insect host. Our results provide insight into the complex response to the host that occurs in a bacterial pathogen, particularly reflecting the potential for metabolic shifts and other specific changes associated with virulence.

Host Plant and Substrate Effects on Mortality of Southern Corn Rootworm from Entomopathogenic Nematodes

Abstract Bioassays were conducted to determine the effects of host plant and substrate type on the susceptibility of Diabrotica undecimpunctata howardi larvae (southern corn rootworm) to entomopathogenic nematodes. Larvae were reared on corn, peanuts, and two squash species. One squash species produces bitter cucurbitacin E, whereas the second squash lacks these secondary compounds. Nematodes of the species Heterorhabditis bacteriophora (Lewiston strain) and Steinernema carpocapsae (Mexican strain) were applied at two concentrations in assays conducted in soil and sand to which rootworm larvae were transferred from different host plants. Host plants and substrate type significantly affected larval susceptibility to both nematode species. The hypothesis that ingested cucurbitacins serve as defense compounds for diabroticites was not supported by the results obtained in this study. D. undecimpunctata howardi larvae suffered higher mortality when reared on both squash species compared to larvae reared on corn or peanuts. Mortality caused by H. bacteriophora was significantly higher in soil than in sand. Generally, S. carpocapsae caused 10 times greater mortality than H. bacteriophora.

Nictation Behaviour and Its Ecological Implications in the Host Search Strategies of Entomopathogenic Nematodes (Heterorhabditidae and Steinernematidae)

[Entomopathogenic nematodes (Heterorhabditidae and Steinernematidae) are insect parasites that appear to use both cruising and ambushing search strategies. Cruising species Heterorhabditis bacteriophora, Steinernema feltiae, and S. glaseri spent more time crawling (88.8, 80.3, and 92.5% of observation period, respectively) and therefore traveled farther (22.4, 18.6, and 24.3 mm, respectively) and searched a larger area (18.3, 13.7, and 26.6 mm2, respectively) than ambushing species. Ambusher species S. carpocapsae and S. scapterisci traveled shorter distances (4.8 and 4.7 mm, respectively) and searched smaller areas (3.0 and 2.5 mm2, respectively) because they spent most of the observation period nictating (77.5 and 78.2%, respectively). Nictating infective juveniles raise greater than 95% of their body off the substrate and maintain a straight posture. A nictating species S. carpocapsae was up to 43 times as effective at finding mobile insect hosts compared to a non-nictating species H. bacteriophora. When unable to nictate host-finding of mobile insects declined from 35.7±7.19 to 3.9±1.11 infective juveniles per host. Nictation, by reducing the surface tension forces holding the nematode to the substrate, can increase the nematodes ability to attach to passing insects. S. carpocapsae also tended to search more effectively along a surface than through a matrix. Although entomopathogenic nematodes have a broad potential host range, differences in search behavior may result in a narrower actual host range. Ambushers being more specialized for mobile insects on the soil surface and cruisers for more sedentary and/or subterranean insects., Entomopathogenic nematodes (Heterorhabditidae and Steinernematidae) are insect parasites that appear to use both cruising and ambushing search strategies. Cruising species Heterorhabditis bacteriophora, Steinernema feltiae, and S. glaseri spent more time crawling (88.8, 80.3, and 92.5% of observation period, respectively) and therefore traveled farther (22.4, 18.6, and 24.3 mm, respectively) and searched a larger area (18.3, 13.7, and 26.6 mm2, respectively) than ambushing species. Ambusher species S. carpocapsae and S. scapterisci traveled shorter distances (4.8 and 4.7 mm, respectively) and searched smaller areas (3.0 and 2.5 mm2, respectively) because they spent most of the observation period nictating (77.5 and 78.2%, respectively). Nictating infective juveniles raise greater than 95% of their body off the substrate and maintain a straight posture. A nictating species S. carpocapsae was up to 43 times as effective at finding mobile insect hosts compared to a non-nictating species H. bacteriophora. When unable to nictate host-finding of mobile insects declined from 35.7±7.19 to 3.9±1.11 infective juveniles per host. Nictation, by reducing the surface tension forces holding the nematode to the substrate, can increase the nematodes ability to attach to passing insects. S. carpocapsae also tended to search more effectively along a surface than through a matrix. Although entomopathogenic nematodes have a broad potential host range, differences in search behavior may result in a narrower actual host range. Ambushers being more specialized for mobile insects on the soil surface and cruisers for more sedentary and/or subterranean insects.]