Foraging Ants as Scavengers on Entomopathogenic Nematode-Killed Insects

Ants were the most apparent invertebrate scavengers observed foraging on entomopathogenic nematode-killed insects (i.e., insect cadavers containing entomopathogenic nematodes and their symbiotic bacteria) in the present study. Workers of the Argentine ant,Linepithema humile(Mayr), scavenged nematode-killed insects on the surface and those buried 2 cm below the soil surface. Ant workers scavenged significantly more steinernematid-killed (60–85%) than heterorhabditid-killed (10–20%) insects. More 4-day-postinfected cadavers (hosts died within 48 h after exposure to nematodes) were scavenged than 10-day-postinfected cadavers. Ten-day-postinfected hosts contained live infective juvenile nematodes therefore ants may serve as phoretic agents. Other ant species, includingVeromessor andrei(Mayr),Pheidole vistanaForel,Formica pacificaFrancoeur, andMonomoriom ergatogynaWheeler, also scavenged nematode-killed insects. These ant species removed or destroyed about 45% of the steinernematid-killed insects. These results suggest that survival of steinernematid nematodes may be more significantly impacted by invertebrate scavengers, especially ants, than that of heterorhabditid nematodes, and placement of steinernematid-killed insects in the field for biological control may be an ineffective release strategy. Because entomopathogenic nematodes kill insects with the help of symbiotic bacteria, we tested the role of these bacterial species in deterring invertebrate scavengers by injecting bacteria (without nematodes) into insects and placing the cadavers in the field. None of the insects killed by the symbiotic bacterium,Photorhabdus luminescens(Thomas and Poinar) fromHeterorhabditis bacteriophoraPoinar, were scavanged, whereas 70% of the insects killed by the symbiotic bacterium,Xenorhabdus nematophilus(Poinar and Thomas) fromSteinernema carpocapsae(Weiser), and 90% of the insects killed byBacillus thuringiensisBerliner were scavenged by the Argentine ant. We conclude thatP. luminescensis responsible for preventing ants from foraging on heterorhabditid-killed hosts.     

Susceptibility of lady beetles (Coleoptera: Coccinellidae) to entomopathogenic nematodes

We investigated differential susceptibility of lady beetles to entomopathogenic nematodes, for two reasons: (1) to estimate potential nontarget effects on natural lady beetle populations, (2) to compare the susceptibility of exotic versus native lady beetle species. We hypothesize that successful establishment of some exotically introduced arthropods may be due, in part, to a lower susceptibility relative to competing native species. In laboratory studies, we compared the pathogenicity, virulence, and reproductive capacity of Heterorhabditis bacteriophora and Steinernema carpocapsae among two native (Coleomegilla maculata and Olla v-nigrum) and two successfully established exotic (Harmonia axyridis and Coccinella septempunctata) lady beetles, and a known susceptible lepidopteran host, Agrotis ipsilon. After 1 and 2 days of exposure to either nematode species, mortality of A. ipsilon was higher than in all lady beetles. Thus, we predict that nematode field applications would have significantly less impact on lady beetle populations than on a susceptible target pest. Additionally, the impact of soil-applied nematodes may be lower on lady beetles than on soil-dwelling hosts because the former spends relatively less time on the soil. Exotic lady beetles were less susceptible to nematode infection than native species. Reproductive capacity data also indicated lower host suitability in H. axyridis, but not in C. septempunctata. Overall, the hypothesis that low susceptibility to pathogens in certain exotic lady beetles may have contributed to competitive establishment was supported (especially for H. axyridis). Additional studies incorporating different hosts and pathogens from various geographic locations will be required to further address the hypothesis.     

The Natural Host Range of Steinernema and Heterorhabditis spp. and Their Impact on Insect Populations

The natural host range of entomopathogenic nematodes of the genera Steinernema and Heterorhabditis can be defined as the range of insects which indigenous nematode populations use for propagation. Information on the natural host range is rare. However, based on records of insects found to be naturally infected with nematodes, some conclusions regarding the natural host range of some Steinernema spp. and Heterorhabditis spp. are presented. Reports of indigenous nematode populations impacting on insect populations can be divided between relatively balanced, long-lasting nematode-host associations and unbalanced, short-lasting epizootics. Examples of the augmentation and inoculative introduction of nematodes in agriculture and forestry ecosystems are presented. Based on current knowledge, nematode reproduction strategies are discussed and indications of the risk involved in the release of non-indigenous nematodes are given.     

Impact of Entomopathogenic Nematodes on Non-target Hosts

Biological pest control has been thought to be ecologically safe for many years. More recently, it has been questioned whether entomopathogens and beneficial arthropods or nematodes truly have no impact on non-target species. Only a few studies deal with the action of entomopathogenic nematodes on non-target animals, although a broad spectrum of species has been tested in the laboratory. Entomopathogenic nematodes do not affect vertebrates under natural conditions. Mortality caused by the release of entomopathogenic nematodes among non-target arthropod populations can occur, but will only be temporary, will be spatially restricted and will affect only part of a population. In plots treated with entomopathogenic nematodes, the impact on the non-target fauna proved to be negligible. The possible impact of introduced exotic nematode species is discussed and regulatory measures for the release are proposed.     

To complete their life cycle, pathogenic nematode-bacteria complexes deter scavengers from feeding on their host cadaver

The life cycle of commercially used molluscicidal rhabditid nematodes Phasmarhabditis hermaphrodita and entomopathogenic steinernematid nematodes is similar: infective stages carry symbiotic bacteria, which kill their host. Nematodes complete their life cycle feeding on the proliferating symbiont and the host tissue. After 1-2 weeks, new infective stages carrying the bacteria leave the host cadaver in search of new hosts. The removal of invertebrate cadavers by scavengers is extremely fast and represents a severe threat to the developing nematodes.Two-choice trials were used to assess prey choice of the generalist predator/scavenger Pterostichus melanarius (Coleoptera: Carabidae) between Deroceras reticulatum (Mollusca: Agriolimacidae) slugs or wax moth Galleria mellonella (Lepidoptera: Pyralidae) larvae killed by infection of P. hermaphrodita/Steinernema affine and control killed by freezing. We demonstrate that the presence of either of the two nematodes tested deters the beetles from consuming infected cadavers. As P. hermaprodita cannot infect an insect host, we hypothesise the deterrent effect being an evolutionary adaptation of the nematode/bacteria complex rather than the ability of the beetles to avoid potentially infective cadavers.     

Generalist entomopathogens as biological indicators of deforestation and agricultural land use impacts on Waikato soils

The relative abundance of entomopathogenic nematodes and fungi was estimated for 10 sites in each of indigenous forest, pasture, and cropland habitats by baiting soil samples with Galleria larvae. The steinernematid Steinernema feltiae (Filip) was the dominant nematode, occurring in soils from all three habitat types. The heterorhabditid Heterorhabditis zelandica Poinar was recovered only from soils of podocarp (Dacrycarpus dacrydioides (A. Rich.)) forests. Galleria infection by nematodes was higher in soils from forest habitat than in soils from pasture and cropland. Among the sampled forests, nematode infection was higher in soils from podocarp stands than those from broadleaf stands. The deuteromycete fungi Beauveria bassiana (Balsamo) Vuillemin, Metarhizium anisopliae (Metschnikoff) Sorokin, and Paecilomyces cf. cicadae (Miquel) Samson, and a Entomophthorales zygomycete, tentatively identified as a Tarchium species, were recovered from the Galleria baits. Infection of Galleria by B. bassiana and M. anisopliae occurred in soils from all habitat types, while that by P. cicadae occurred only in soils from forest habitats. Tarchium was recovered from a single pasture site. The frequency of Galleria infection by these entomopathogenic fungi collectively, and by B. bassiana alone, was higher in pasture soils than in soils from either forest or cropland. These results are discussed in relation to disturbance effects of land use changes and the potential role of generalist entomopathogens as biological indicators of soil health.     

Growth-mediated variations in fatty acids of Xenorhabdus sp

The bacterium Xenorhabdus sp. is symbiotically associated with the entomopathogenic nematode Steinernema riobravis. This nematode is produced in monoxenic culture with Xenorhabdus sp. and is sold as a biological insecticide. Acceptable yields in fermentors can only be achieved in the presence of vigorous growth of the bacterium. We investigated the fatty acid composition of Xenorhabdus species when grown at 15, 20, 25 or 30 degrees C on media containing one of two primary carbon sources: glucose or lipids from the insect host, Galleria mellonella. Both temperature and primary carbon source significantly affected lipid quantity and quality in Xenorhabdus sp. Bacteria grown with insect lipids as a primary carbon source accumulated more lipids with greater proportion of longer chain fatty acids than bacteria grown with glucose as a primary carbon source. Cells grown with insect lipids at 15 degrees C had a lower lipid content than cells grown on the same media at 20, 25 or 30 degrees C. Increasing growth temperature increased saturated fatty acids and decreased unsaturated fatty acids, irrespective of carbon source. We recommend addition of complex fatty acid sources that resemble natural host lipids to growth medium for mass producing entomopathogenic nematodes. This could provide nematode quality similar to in vivo-produced nematodes.     

Comparative study of the entomopathogenic nematode, Steinernema carpocapsae, reared on mutant and wild-type Xenorhabdus nematophila

The symbiotic interaction between Steinernema carpocapsae and Xenorhabdus nematophila was investigated by comparing the reproduction, morphology, longevity, behavior, and efficacy of the infective juvenile (IJ) from nematodes reared on mutant or wild-type bacterium. Nematodes reared on the mutant X. nematophila HGB151, in which an insertion of the bacterial gene, rpoS, eliminates the retention of the bacterium in the intestinal vesicle of the nematode, produced IJs without their symbiotic bacterium. Nematodes reared on the wild-type bacterium (HGB007) produced IJs with their symbiotic bacterium. One or the other bacterial strain injected into Galleria mellonella larvae followed by exposing the larvae to IJs that were initially symbiotic bacterium free produced progeny IJs with or without their Xenorhabdus-symbiotic bacterium. The two bacterial strains were not significantly different in their effect on IJ production, sex ratio, or IJ morphology. IJ longevity in storage was not influenced by the presence or absence of the bacterial symbiont at 5 and 15 °C, but IJs without their bacterium had greater longevity than IJs with their bacterium at 25 and 30 °C, suggesting that there was a negative cost to the nematode for maintaining the bacterial symbiont at these temperatures. IJs with or without their symbiotic bacterium were equally infectious to Spodoptera exigua larvae in laboratory and greenhouse and across a range of soil moistures, but the absence of the bacterial symbiont inhibited nematodes from producing IJ progeny within the host cadavers. In some situations, such as where no establishment of an alien entomopathogenic nematode is desired in the environment, the use of S. carpocapsae IJs without their symbiotic bacterium may be used to control some soil insect pests.     

When mutualists are pathogens: an experimental study of the symbioses between Steinernema (entomopathogenic nematodes) and Xenorhabdus (bacteria)

In this paper, we investigate the level of specialization of the symbiotic association between an entomopathogenic nematode (Steinernema carpocapsae) and its mutualistic native bacterium (Xenorhabdus nematophila). We made experimental combinations on an insect host where nematodes were associated with non-native symbionts belonging to the same species as the native symbiont, to the same genus or even to a different genus of bacteria. All non-native strains are mutualistically associated with congeneric entomopathogenic nematode species in nature. We show that some of the non-native bacterial strains are pathogenic for S. carpocapsae. When the phylogenetic relationships between the bacterial strains was evaluated, we found a clear negative correlation between the effect a bacterium has on nematode fitness and its phylogenetic distance to the native bacteria of this nematode. Moreover, only symbionts that were phylogenetically closely related to the native bacterial strain were transmitted. These results suggest that co-evolution between the partners has led to a high level of specialization in this mutualism, which effectively prevents horizontal transmission. The pathogenicity of some non-native bacterial strains against S. carpocapsae could result from the incapacity of the nematode to resist specific virulence factors produced by these bacteria.     

不同昆虫寄主对昆虫病原线虫共生菌的敏感性比较

用菜青虫、棉铃虫、甜菜夜蛾、玉米螟、粘虫、黄粉虫等 6种昆虫对 1 0株昆虫病原线虫共生菌进行了敏感性测定。结果表明 :供试菌株对 6种昆虫都有胃毒活性 ,不同菌株对同一种昆虫的毒力差别较大 ,同一菌株对不同昆虫差别也很大。 1 0株菌在 1 2 0h对菜青虫的校正死亡率和体重抑制率均最高 ,显然是最敏感的寄主。在 1 0株共生菌中 ,XenorhabdusnematophilaHB3 1 0 5 9菌株的胃毒活性最高。     

The bacterial community of entomophilic nematodes and host beetles

Insects form the most species‐rich lineage of Eukaryotes and each is a potential host for organisms from multiple phyla, including fungi, protozoa, mites, bacteria and nematodes. In particular, beetles are known to be associated with distinct bacterial communities and entomophilic nematodes. While entomopathogenic nematodes require symbiotic bacteria to kill and reproduce inside their insect hosts, the microbial ecology that facilitates other types of nematode–insect associations is largely unknown. To illuminate detailed patterns of the tritrophic beetle–nematode–bacteria relationship, we surveyed the nematode infestation profiles of scarab beetles in the greater Los Angeles area over a five‐year period and found distinct nematode infestation patterns for certain beetle hosts. Over a single season, we characterized the bacterial communities of beetles and their associated nematodes using high‐throughput sequencing of the 16S rRNA gene. We found significant differences in bacterial community composition among the five prevalent beetle host species, independent of geographical origin. Anaerobes Synergistaceae and sulphate‐reducing Desulfovibrionaceae were most abundant in Amblonoxia beetles, while Enterobacteriaceae and Lachnospiraceae were common in Cyclocephala beetles. Unlike entomopathogenic nematodes that carry bacterial symbionts, insect‐associated nematodes do not alter the beetles' native bacterial communities, nor do their microbiomes differ according to nematode or beetle host species. The conservation of Diplogastrid nematodes associations with Melolonthinae beetles and sulphate‐reducing bacteria suggests a possible link between beetle–bacterial communities and their associated nematodes. Our results establish a starting point towards understanding the dynamic interactions between soil macroinvertebrates and their microbiota in a highly accessible urban environment.     

Laboratory studies on the competition for insect haemocoel between Beauveria bassiana and Steinernema ichnusae recovered in the same ecological niche

Laboratory assays evaluated the combined action of the entomopathogenic nematode Steinernema ichnusae and the entomopathogenic fungus Beauveria bassiana isolated from the same ecological niche, an oak forest in Sardinia (Italy). Galleria mellonella larvae were used as the test insect with the aim of understanding what happens in host haemocoel during a simultaneous infection with two different entomopathogens. Larval mortality assays were performed using nematodes and fungi both alone and together, at the same and different times, and in different concentrations. No additive or synergistic effects were observed, but there was a clear antagonism and competition for survival space in the haemocoel. Moreover, mutual effects between the symbiotic bacteria of the entomopathogenic nematode Xenorhabdus bovienii and entomopathogenic fungi were investigated. In laboratory experiments, X. bovienii crude extracts were tested for their activity against fungal growth. Compounds produced by B. bassiana were tested for their activity against the growth of bacteria, revealing that X. bovienii and B. bassiana are antagonistic to each other.     

Bionomics of a Phoretic Association Between Paenibacillus sp. and the Entomopathogenic Nematode Steinernema diaprepesi

Spores of an unidentified bacterium were discovered adhering to cuticles of third-stage infective juvenile (IJ) Steinernema diaprepesi endemic in a central Florida citrus orchard. The spores were cup-shaped, 5 to 6 mm in length, and contained a central endospore. Based on 16S rDNA gene sequencing, the bacterium is closely related to the insect pathogens Paenibacillus popilliae and P. lentimorbus. However, unlike the latter bacteria, the Paenibacillus sp. is non-fastidious and grew readily on several standard media. The bacterium did not attach to cuticles of several entomopathogenic or plant-parasitic nematodes tested, suggesting host specificity to S. diaprepesi. Attachment of Paenibacillus sp. to the third-stage cuticle of S. diaprepesi differed from Paenibacillus spp. associated with heterorhabditid entomopathogenic nematodes, which attach to the IJ sheath (second-stage cuticle). The inability to detect endospores within the body of S. diaprepesi indicates that the bacterial association with the nematode is phoretic. The Paenibacillus sp. showed limited virulence to Diaprepes abbreviatus, requiring inoculation of larvae with 108 spores to achieve death of the insect and reproduction of the bacterium. The effect of the bacterium on the nematode population biology was studied in 25-cm-long vertical sand columns. A single D. abbreviatus larva was confined below 15-cm depth, and the soil surface was inoculated with either spore-free or spore-encumbered IJ nematodes. After 7 days, the proportion of IJ below 5-cm depth was seven-fold greater for spore-free IJ than for spore-encumbered nematodes. Mortality of D. abbreviatus larvae was 72% greater (P <= 0.01) for spore-free compared to spore-encumbered S. diaprepesi. More than 5 times as many progeny IJs (P <= 0.01) were produced by spore-free compared to spore-encumbered nematodes. These data suggest that the bacterium is a component of the D. abbreviatus food web with some potential to regulate a natural enemy of the insect.     

Temperature effects on Korean entomopathogenic nematodes, Steinernema glaseri and S. longicaudum, and their symbiotic bacteria

We investigated the temperature effects on the virulence, development, reproduction, and motility of two Korean isolates of entomopathogenic nematodes, Steinernema glaseri Dongrae strain and S. longicaudum Nonsan strain. In addition, we studied the growth and virulence of their respective symbiotic bacterium, Xenorhabdus poinarii for S. glaseri and Xenorhabdus sp. for S. longicaudum, in an insect host at different temperatures. Insects infected with the nematode-bacterium complex or the symbiotic bacterium was placed at 13 degrees C, 18 degrees C, 24 degrees C, 30 degrees C, or 35 degrees C in the dark and the various parameters were monitored. Both nematode species caused mortality at all temperatures tested, with higher mortalities occurring at temperatures between 24 degrees C and 30 degrees C. However, S. longicaudum was better adapted to cold temperatures and caused higher mortality at 18 degrees C than S. glaseri. Both nematode species developed to adult at all temperatures, but no progeny production occurred at 13 degrees C or 35 degrees C. For S. glaseri, nematode progeny production was best at inocula levels above 20 infective juveniles/host at 24 degrees C and 30 degrees C, but for S. longicaudum, progeny production was generally better at 24 degrees C. Steinernema glaseri showed the greatest motility at 30 degrees C, whereas S. longicaudum showed good motility at 24 degrees C and 30 degrees C. Both bacterial species grew at all tested temperatures, but Xenorhabdus sp. was more virulent at low temperatures (13 degrees C and 18 degrees C) than X poinarii.     

Potentiating effect of Bacillus thuringiensis subsp. kurstaki on pathogenicity of entomopathogenic bacterium Xenorhabdus nematophila K1 against diamondback moth (Lepidoptera: Plutellidae)

Xenorhabdus nematophila is the symbiotic bacterium of an entomopathogenic nematode, Steinernema carpocapsae. When the nematode enters a target insect, the symbiotic bacteria are released into the hemocoel. After inducing host immunosuppression, the bacteria multiply in the hemocoel and cause fatal septicemia. For optimal field application to control insect pests, culturing mass numbers of the nematodes would be costly. In this study, Bacillus thuringiensis (Bt) was chosen as an alternative natural vector, which would be relatively economical for field application. Bt infection of gut epithelium would form a bacterial passage between the gut lumen and hemocoel, which facilitates the orally fed X. nematophila to infect the hemocoel. Diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), used in this study was tolerant to Bt because only 10% mortality was noted in response to 2 times higher concentration than recommended for commercial B. t. kurstaki, although this species was susceptible only during early instars. The orally fed X. nematophila caused significant mortality to early instars of P. xylostella, but not late instars. When both X. nematophila and Bt were fed to late instars of P. xylostella, they showed significantly enhanced mortality, in which X. nematophila cells were recovered from the hemocoel of the treated P. xylostella. However, when only X. nematophila was fed, no cells were recovered from the hemolymph. This study suggests that X. nematophila can be applied to control P. xylostella in a mixture with Bt in the field without its nematode host.     

Effect of Photorhabdus luminescens phase variants on the in vivo and in vitro development and reproduction of the entomopathogenic nematodes Heterorhabditis bacteriophora and Steinernema carpocapsae

Photorhabdus luminescens (Enterobacteriaceae) is a symbiont of entomopathogenic nematodes Heterorhabditis spp. (Nematoda: Rhabditida) used for biological control of insect pests. For industrial mass production, the nematodes are produced in liquid media, pre-incubated with their bacterial symbiont, which provides nutrients essential for the nematode's development and reproduction. Particularly under in vitro conditions, P. luminescens produces phase variants, which do not allow normal nematode development. The phase variants were distinguished based on dye absorption, pigmentation, production of antibiotic substances, occurrence of crystalline inclusion proteins and bioluminescence. To understand the significance of the phase shift for the symbiotic interaction between the bacterium and the nematode, feeding experiments tested the effect of homologous and heterologous P. luminescens phase variants isolated from a Chinese Heterorhabditis bacteriophora (HO6), the Heterorhabditis megidis type strain from Ohio (HNA) and the type strain of Heterorhabditis indica (LN2) on the in vivo and in vitro development and reproduction of the nematode species H. bacteriophora (strain HO6) and another rhabditid and entomopathogenic nematode, Steinernema carpocapsae (A24). In axenically cultured insect larvae (Galleria mellonella) and in vitro in liquid media, H. bacteriophora produced offspring on phase I of its homologous symbiont and on the heterologous symbiont of H. megidis, but not on the two corresponding phase II variants. In solid media, nematode yields were much lower on phase II than on phase I variants. On the heterologous phase I symbiont isolated from H. indica the development of H. bacteriophora was not beyond the fourth juvenile stage of the nematode in any of the media tested, but further progressed on phase II with even a small amount of offspring recorded in solid media. Infective juveniles of S. carpocapsae did not develop beyond the J3 stage on all phase I P. luminescens. They died in phase I P. luminescens isolated from H. bacteriophora. Development to adults was recorded for S. carpocapsae on all phase II symbionts and offspring were produced in all media except in liquid. It is concluded that a lack of essential nutrients or the production of toxins is not responsible for the negative impact of homologous phase II symbiont cells on the development and reproduction of H. bacteriophora. The infective juveniles of H. bacteriophora retained cells of the homologous phase I symbiont, but not phase II cells and cells from heterologous symbionts, indicating that the transmission of the symbiont by the infective juvenile is selective for phase I cells and the homologous bacterial associate.     

Legislation on the Introduction of Exotic Entomopathogenic Nematodes into Australia and New Zealand

There are stringent requirements for the importation of all exotic organisms into Australia and New Zealand but since both countries have already permitted the importation and release of some species of both Heterorhabditis and Steinernema , the difficulties of the importation of entomopathogenic nematodes are reduced. In both countries, a series of authorities must be consulted before importation is permitted but only in New Zealand must entomopathogenic nematodes be registered before commercial trials and sales are allowed. Registration not only entails a thorough evaluation of the nematode species and its formulation for a wide range of possible harmful effects to humans, crops and the environment, but efficacy must be demonstrated for each species of nematode in each type of formulation against each pest.     

Ecology in the service of biological control: the case of entomopathogenic nematodes

 Biological control manipulations of natural enemies to reduce pest populations represent large-scale ecological experiments that have both benefited from and contributed to various areas of modern ecology. Unfortunately, economic expediency and the need for rapid implementation often require that biological control programs be based more on trial and error than on sound ecological theory and testing. This approach has led to some remarkable successes but it has also produced dismal failures. This point is particularly well illustrated in the historical development and use of entomopathogenic nematodes for the biological control of insect pests. Intense effort has focused on developing these natural enemies as alternatives to chemical insecticides, in part because laboratory assays indicated that these nematodes possess a broad host range. This illusory attribute launched hundreds of field releases, many of which failed due to ecological barriers to infection that are not apparent from laboratory exposures, where conditions are optimal and host-parasite contact assured. For example, the entomopathogenic nematode Steinernema carpocapsae is a poor choice to control scarab larvae because this nematode uses an ambusher foraging strategy near the soil surface whereas the equally sedentary scarab remains within the soil profile, shows a weak host recognition response to scarabs, has difficulty overcoming the scarab immune response, and has low reproduction in this host. Conversely, two other nematodes, Heterorhabditis bacteriophora and S. glaseri, are highly adapted to parasitize scarabs: they use a cruising foraging strategy, respond strongly to scarabs, easily overcome the immune response, and reproduce well in these hosts. Increased understanding of the ecology of entomopathogenic nematodes has enabled better matches between parasites and hosts, and more accurate predictions of field performance. These results underline the importance of a strong partnership between basic and applied ecology in the area of biological control. Received: 15 July 1996 / Accepted: 5 November 1996     

Parameters affecting plant defense pathway mediated recruitment of entomopathogenic nematodes

Entomopathogenic nematodes are natural enemies and effective biological control agents of subterranean insect herbivores. Interactions between herbivores, plants, and entomopathogenic nematodes are mediated by plant defense pathways. These pathways can induce release of volatiles and recruit entomopathogenic nematodes. Stimulation of these plant defense pathways for induced defense against belowground herbivory may enhance biological control in the field. Knowledge of the factors affecting entomopathogenic nematode behaviour belowground is needed to effectively implement such strategies. To that end, we explore the effect of elicitor, elicitor dose, mechanical damage, and entomopathogenic nematode release distance on recruitment of entomopathogenic nematode infective juveniles to corn seedlings. Increasing doses of methyl jasmonate and methyl salicylate elicitors recruited more entomopathogenic nematodes as did mechanical damage. Recruitment of entomopathogenic nematodes was higher at greater release distances. These results suggest entomopathogenic nematodes are highly tuned to plant status and present a strategy for enhancing biological control using elicitor-stimulated recruitment of entomopathogenic nematodes.     

七种我国昆虫病原线虫共生菌的分离与鉴定

昆虫病原线虫共生菌是一类具有广阔发展前景的生物防治资源,由于这类菌的分类鉴定工作起步晚,存在分类混乱和不系统的现象,在本土资源十分丰富的我国尤为突出.本文对本实验室分离的7个共生菌菌株进行了分类描述,建立了以生理形态,生化特征为分类基础,结合16 SrDNA序列分析的有效鉴定方法.