The comparative biology of two sympatric paper wasps in Michigan,the native <Emphasis Type="Italic">Polistes fuscatus</Emphasis> and the invasive <Emphasis Type="Italic">Polistes dominulus</Emphasis> (Hymenoptera,Vespidae)

Summary The biology of the invasive Polistes dominulus and the native P. fuscatus was compared at a field site in Rochester, Michigan over a two-year period. Colonies nesting semi-naturally in plywood nestboxes were studied using videography, extensive surveys, and colony-specific marking of gynes.Both single- and multiple-foundress colonies of P. dominulus were significantly more productive than comparable colonies of P. fuscatus. The disparity in productivity was significantly more pronounced in single-foundress colonies than in multiple-foundress colonies. P. dominulus had significantly shorter larval and pupal development times than P. fuscatus, which allowed P. dominulus to produce its first workers about a week earlier than P. fuscatus. P. dominulus had a number of additional advantages over P. fuscatus that contributed to its productivity including (1) significantly less parasitism by Strepsiptera, (2) significantly greater probability of renesting after predation by raccoons, (3) significantly lower usurpation pressures, and (4) possibly longer foraging days . The recovery of colony-marked foundresses indicated that gynes of P. dominulus suffered significantly greater mortality than gynes of P. fuscatus during winter diapause and that foundresses of both species were equally, strongly philopatric.P. dominulus is likely replacing P. fuscatus in many areas of southeastern Michigan via indirect or exploitative competition. The two species may be competing for nest sites.Received 7 July 2003; revised 10 October 2003; accepted 3 November 2003.     

The relationships between cuticular hydrocarbon composition, faunal assemblages, inter-island distance, and population genetic variation in Tuscan Archipelago wasps

Until recently, studies examining the geographical distribution of insects in the Tuscan Archipelago have focused on paleogeography as the primary influence on species distributions. However, for flying insects such as Hymenoptera that may be able to disperse over water, current geographical location is likely to be more important in determining present distributions within the Archipelago. Here we compare mainland and island wasp populations using genetic variation and cuticular hydrocarbon composition of the vespid wasp Polistes dominulus, and species composition of wasps in the family Pompilidae. Both chemical and genetic data result in similar clustering of P. dominulus populations that reflect present geographical location. Moreover, we found current geographical distance to be significantly correlated with P. dominulus population genetic differentiation and Pompilidae faunal composition. These data suggest that dispersal over present sea distances is more important in determining population differentiation and species distribution in the Tuscan Archipelago than paleogeography.     

Dynamics of potentially harmful microalgae in a confined Mediterranean Gulf—Assessing the risk of bloom formation

The population dynamics of potentially harmful microalgae was investigated in the semi-enclosed shallow Gulf of Kalloni, Greece (Aegean Sea, Eastern Mediterranean), during a 2-year period from August 2004 to March 2006. A total of 21 potentially harmful microalgae (bloom-forming and/or toxic) were identified including 3 diatoms and 18 dinoflagellates. The densities of each species were analyzed in time and space and in relation to environmental parameters. Some species such as Alexandrium insuetum, Heterocapsa circularisquama, Karlodinium veneficum, Scrippsiella trochoidea, and Ceratium spp. developed high cell concentrations, particularly during a Pseudo-nitzschia calliantha winter bloom. Other species such as Dinophysis caudata, Ostreopsis ovata, Prorocentrum minimum, and Protoperidinium crassipes were rare or appeared in small numbers. Densities of the most abundant species were closely associated with freshwater nutrient-rich inputs during winter, being negatively correlated with temperature and salinity and positively correlated with nitrogen. The spatial distribution of the abundant species exhibited a marked increase towards the inner part of the gulf, close to the main freshwater inputs, whereas some species were mainly concentrated in the dilute surface layer (1 m depth). Examination of the abundance–occupancy relationship revealed that the species more prone to bloom are those with wide spatial distribution and frequent presence throughout the year such as the diatom P. calliantha. Although blooms of cyst-forming species are rarer, an increased risk can be foreseen under favorable resource supply and environmental conditions during winter.     

Wolbachia in the invasive European paper wasp Polistes dominulus

The European paper wasp Polistes dominulus has been expanding its North American range since its introduction in the 1970s. We screened P. dominulus from Italy and the northeastern U.S. for the presence of the intracellular reproductive symbiont Wolbachia. Infection rates among females varied from 16% to 87% among U.S. sites and from 33% to 71% in Italy. We also found infected haploid and diploid males, indicating that this is not a male-killing Wolbachia infection. Our data show that infected individuals from New York, Massachusetts, and Italy carry the same Wolbachia strain, and that some mtDNA haplotypes include both infected and uninfected individuals. We discuss possible implications of Wolbachia infection in this invasive social hymenopteran. Received 28 October 2005; revised 25 January 2006; accepted 17 February 2006.     

Antibacterial activity of larval saliva of the European paper wasp <Emphasis Type="Italic">Polistes dominulus</Emphasis> (Hymenoptera,Vespidae)

Summary. Microbiological tests demonstrated antibacterial activity (against Bacillus subtilis, Gram +, and Escherichia coli, Gram –) of larval salivary secretions of Polistes dominulus but failed to demonstrate its antifungal activity.Received 7 November 2003; revised 17 March 2004; accepted 29 March 2004.     

Field Release and Establishment of the Decapitating Fly Pseudacteon curvatus on Red Imported Fire Ants in Florida

Decapitating phorid flies in the genus Pseudacteon are being studied as classical biological control agents of the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae). Pseudacteon curvatus Borgmeier (Diptera: Phoridae) is a small decapitating fly that attacks small fire ant workers. We released a biotype of P. curvatus from Formosa, Argentina, at three sites near Gainesville, FL. Field releases were conducted in the spring and summer of 2003 and monitored monthly. Flies were discovered within 5 weeks at the spring site and then monthly thereafter. By late spring 2004, flies released at this site had expanded 1.6 km both north and south and about 0.8 km westward. Initially, we found no flies from the two summer 2003 releases but we were successful at finding them 8 months after release during spring 2004. This paper documents the first successful release(s) of P. curvatus on red imported fire ants in the United States.     

不同营养盐条件下赤潮高发区围隔生态系内多胺的变化

在东海赤潮爆发区域运用围隔生态系实验方法,研究了不同营养盐条件下围隔生态系内多胺浓度变化。结果表明:2010年选用东海原甲藻赤潮爆发处海水,东海原甲藻是各围隔生态系内主要优势种,没有种群演替现象发生。两种营养盐添加方式下各围隔内精胺浓度维持较高水平,都呈现先波折下降后波折上升的趋势,与东海原甲藻的生长变化正好相反;各围隔内腐胺浓度水平较高,变化起伏较大,其中有两个实验组腐胺整体变化趋势与东海原甲藻生长趋势类似;所有围隔内亚精胺浓度最低,波动较小。2011年取用中肋骨条藻赤潮爆发处海水,所有围隔生态系内优势种都发生了从中肋骨条藻到东海原甲藻的演替。各围隔生态系内腐胺浓度最高,在中肋骨条藻生长初期腐胺浓度下降,随着中肋骨条藻的生长有所上升,实验后期随着东海原甲藻的生长又整体呈现出下降趋势;各实验组精胺浓度较低,在中肋骨条藻消亡东海原甲藻出现的种群演替期间,都呈现出较大波动;各围隔内亚精胺浓度较低,在整个种群演替过程中没有明显的变化。围隔生态系中补充营养盐,通过对浮游植物生长的影响,间接影响围隔生态系内的多胺变化。     

Effects of the estuarine dinoflagellate Pfiesteria shumwayae (Dinophyceae) on survival and grazing activity of several shellfish species

A series of experiments was conducted to examine effects of four strains of the estuarine dinoflagellate, Pfiesteria shumwayae, on the behavior and survival of larval and adult shellfish (bay scallop, Argopecten irradians; eastern oyster, Crassostrea virginica; northern quahogs, Mercenaria mercenaria; green mussels, Perna viridis [adults only]). In separate trials with larvae of A. irradians, C. virginica, and M. mercenaria, an aggressive predatory response of three strains of algal- and fish-fed P. shumwayae was observed (exception, algal-fed strain 1024C). Larval mortality resulted primarily from damage inflicted by physical attack of the flagellated cells, and secondarily from Pfiesteria toxin, as demonstrated in larval C. virginica exposed to P. shumwayae with versus without direct physical contact. Survival of adult shellfish and grazing activity depended upon the species and the cell density, strain, and nutritional history of P. shumwayae. No mortality of the four shellfish species was noted after 24 h of exposure to algal- or fish-fed P. shumwayae (strains 1024C, 1048C, and CCMP2089) in separate trials at ≤5 × 10³ cells ml⁻¹, whereas higher densities of fish-fed, but not algal-fed, populations (>7–8 × 10³ cells ml⁻¹) induced low (≤15%) but significant mortality. Adults of all four shellfish species sustained >90% mortality when exposed to fish-fed strain 270A1 (8 × 10³ cells ml⁻¹). In contrast, adult M. mercenaria and P. viridis exposed to a similar density of fish-fed strain 2172C sustained <15% mortality, and there was no mortality of A. irradians and C. virginica exposed to that strain. In mouse bioassays with tissue homogenates (adductor muscle, mantle, and whole animals) of A. irradians and M. mercenaria that had been exposed to P. shumwayae (three strains, separate trials), mice experienced several minutes of disorientation followed by recovery. Mice injected with tissue extracts from control animals fed cryptomonads showed no response. Grazing rates of adult shellfish on P. shumwayae (mean cell length ±1 standard error [S.E.], 9 ± 1 μm) generally were significantly lower when fed fish-fed (toxic) populations than when fed populations that previously had been maintained on algal prey, and grazing rates were highest with the nontoxic cryptomonad, Storeatula major (cell length 7 ± 1 μm). Abundant cysts of P. shumwayae were found in fecal strands of all shellfish species tested, and ≤45% of the feces produced viable flagellated cells when placed into favorable culture conditions. These findings were supported by a field study wherein fecal strands collected from field-collected adult shellfish (C. virginica, M. mercenaria, and ribbed mussels, Geukensia demissa) were confirmed to contain cysts of P. shumwayae, and these cysts produced fish-killing flagellated populations in standardized fish bioassays. Thus, predatory feeding by flagellated cells of P. shumwayae can adversely affect survival of larval bivalve molluscs, and grazing can be depressed when adult shellfish are fed P. shumwayae. The data suggest that P. shumwayae could affect recruitment of larval shellfish in estuaries and aquaculture facilities; shellfish can be adversely affected via reduced filtration rates; and adult shellfish may be vectors of toxic P. shumwayae when shellfish are transported from one geographic location to another.     

Spread and persistence of a rugulosin-producing endophyte in Picea glauca seedlings

We have studied Picea glauca (white spruce) endophyte colonization and its affect on the growth of Choristoneura fumiferana (spruce budworm). Here we examine the spread and persistence of a rugulosin-producing endophyte and rugulosin in needles from trees maintained in the nursery, as well as in trees planted in a test field site. Additionally, we report toxicity of rugulosin against three P. glauca needle herbivores: C. fumiferana, Lambdina fiscellaria (hemlock looper) and Zeiraphera canadensis (spruce budmoth). Reduction in body weight for both the C. fumiferana and L. fiscellaria were observed at 25 and 50 μm, respectively, and head capsules were reduced at 100 and 150 μm. Z. canadensis larvae did not perform as well in tests due to an Aspergillus fumigatus infection, but were shown to be lighter when tested with 100 and 150 μm compared with controls. The endophyte and its toxin were shown to spread throughout the nursery-grown seedlings. After 3.5 and 4.5 y post-inoculation (one and two years in the test site), the inoculated endophyte and its toxin had remained present with an average rugulosin concentration of 1 μg g⁻¹.     

Yersinia enterocolitica type III secretion chaperone SycH. Recombinant expression, purification, characterisation, and crystallisation

All pathogenic Yersinia species (Y. enterocolitica, Y. pestis, and Y. pseudotuberculosis) share a type three secretion system (TTSS) that allows translocation of effector proteins into host cells. Yersinia enterocolitica SycH is a chaperone assisting the transport of the effector YopH and two regulatory components of the TTSS, YscM1 and YscM2. We have recombinantly expressed SycH in Escherichia coli. Purification of tag-free SycH to near homogeneity was achieved by combining ammonium sulfate precipitation, anion exchange chromatography, and gel filtration. Functionality of purified SycH was proven by demonstrating binding to YopH. SycH crystals were grown that diffracted to 2.94 Å resolution. Preliminary crystallographic data and biochemical findings suggest that SycH forms homotetramers. SycH may therefore represent a novel class of TTSS chaperones. In addition, we found that YopH was enzymatically active in the presence of SycH. This implies that the function of the secretion chaperone SycH is not to keep YopH in a globally unfolded state prior to secretion.     

Phytophthora quercetorum sp. nov., a novel species isolated from eastern and north-central USA oak forest soils

Isolates belonging to an undescribed Phytophthora species were frequently recovered during an oak forest soil survey of Phytophthora species in eastern and north-central USA in 2004. The species was isolated using an oak leaf baiting method from rhizosphere soil samples collected from Quercus rubra, Q. macrocarpa, and Q. phellos. This species is formally described as P. quercetorum. It is homothallic and has aplerotic oogonia and paragynous antheridia. It produces papillate sporangia (occasionally bipapillate) of ovoid-elongated shapes. Its temperature optimum for growth is ca 22.5 °C with the upper limit of ca 32.5 °C. P. quercetorum differs from the morphologically related P. quercina in producing distinct submerged colony-patterns, different growth-temperature requirements, and oogonial shapes and sizes. Phylogenetic analyses using seven nuclear loci supported P. quercetorum as a novel species within clade 4, closely related to P. arecae, P. palmivora, P. megakarya, and P. quercina.     

Cytogenetic analysis of metaphase chromosomes from pupal testes of four mosquito species using fluorescence <Emphasis Type="Italic">in situ</Emphasis> hybridization technique (FISH)

The DNA probes, P1887, P2405, P2056 (being specific tags for Aedes aegypti genes coding for ribosomal RNA) and a centric heterochromatin probe, K20-1A5, were chosen to hybridize the metaphase chromosomes from the testes of four mosquito species, Culex pipiens, Aedes aegypti, Aedes albopictus and Aedes triseriatus. In addition, a single plasmid, P2392, which contained the three probes, P1887, P2405 and P2056, was also used as chromosome landmark in aedine species. Only the Aedes aegypti metaphase chromosome 1-specific tag, P1887, was conserved in Aedes albopictus, Aedes triseriatus, and Culex pipiens metaphase chromosomes. Aedes triseriatus exhibited two gene loci, on chromosomes 1 and 3, coding for ribosomal RNA per haploid genome. When the specific probes for chromosomes 2 and 3, 2405 and 2056, were used in the fluorescence in situ hybridization technique against the metaphase chromosomes the fluorescent signals were not seen in Aedes albopictus, Aedes triseriatus or Culex pipiens. Also the centric heterochromatin probe, K20-1A5, exhibited strong fluorescent signals on chromosomes 1, 2 and 3 of Aedes aegypti. These fluorescent signals were not observed in metaphase chromosomes derived from the other aedine species, indicating that the centromere sequence can vary within the species.This paper was presented at the Second Arab Conference on Biotechnology and Genetic Engineering, held in the Kingdom of Bahrain, 15–17 April, 2002 and is published here with the endorsement of the Co-ordinator of the Scientific Committee, Professor Essam H. Ghanem, University of Bahrain. Its publication has been delayed because of the ill health of the senior author. Other papers from this conference were published in the July 2003 issue (vol. 19, no. 5).     

Comparative analysis of the reproductive biology of two Peristenus species (Hymenoptera: Braconidae), biological control agents of Lygus plant bugs (Hemiptera: Miridae)

Peristenus digoneutis Loan and Peristenus stygicus Loan, parasitoids of the European tarnished plant bug Lygus rugulipennis Poppius, are established in the United States for biological control of native North American Lygus species, and are being considered for deliberate release in Canada. High lifetime fecundity of parasitoids is considered a desirable attribute of biological control agents and therefore, an understanding of parasitoid reproductive biology is required. In the present study, the potential lifetime fecundity of both agents was compared under laboratory conditions to estimate the potential impact of Peristenus species on Lygus. Synovigenic P. digoneutis and P. stygicus females oviposited most actively in the first two weeks of their lifetime, with a maximum average daily oviposition rate after five days. The maximum number of eggs laid per day was 83 eggs for P. stygicus, and 36 eggs for P. digoneutis. P. digoneutis has an average potential lifetime fecundity of 385 ± 35 SE eggs produced over 22 ± 3 SE days. In contrast, P. stygicus females have a 50% higher mean potential lifetime fecundity reaching 782 ± 65 SE eggs over 28 ± 1 SE days. A positive correlation between lifetime fecundity and body size was found only for P. stygicus, and both species showed a significant relationship between lifetime fecundity and oviposition period. The present study demonstrates that the fecundity of P. digoneutis and P. stygicus is considerably higher than previously reported. Based on these findings, P. stygicus appears to be the most effective biological control agent for Lygus lineolaris (Palisot de Beauvois) when only fecundity is taken into consideration.     

The type III secretion system is involved in Escherichia coli K1 interactions with Acanthamoeba

The type III secretion system among Gram-negative bacteria is known to deliver effectors into host cell to interfere with host cellular processes. The type III secretion system in Yersina, Pseudomonas and Enterohemorrhagic Escherichia coli have been well documented to be involved in the bacterial pathogenicity. The existence of type III secretion system has been demonstrated in neuropathogenic E. coli K1 strains. Here, it is observed that the deletion mutant of type III secretion system in E. coli strain EC10 exhibited defects in the invasion and intracellular survival in Acanthamoeba castellanii (a keratitis isolate) compared to its parent strain. Next, it was determined whether type III secretion system plays a role in E. coli K1 survival inside Acanthamoeba during the encystment process. Using encystment assays, our findings revealed that the type III secretion system-deletion mutant exhibited significantly reduced survival inside Acanthamoeba cysts compared with its parent strain, EC10 (P < 0.01). This is the first demonstration that the type III secretion system plays an important role in E. coli interactions with Acanthamoeba. A complete understanding of how amoebae harbor bacterial pathogens will help design strategies against E. coli transmission to the susceptible hosts.     

Ferrihydrite reduction by Geobacter species is stimulated by secondary bacteria

Geobacter species such as G. bremensis, G. pelophilus, and G. sulfurreducens are obligately anaerobic and grow in anoxic, non-reduced medium by fast reduction of soluble ferric citrate. In contrast, insoluble ferrihydrite was either only slowly or not reduced when supplied as electron acceptor in similar growth experiments. Ferrihydrite reduction was stimulated by addition of a reducing agent or by concomitant growth of secondary bacteria that were physiologically and phylogenetically as diverse as Escherichia coli, Lactococcus lactis, or Pseudomonas stutzeri. In control experiments with heat-inactivated Geobacter cells and viable secondary bacteria, no (E. coli, P. stutzeri) or only little (L. lactis) ferrihydrite was reduced. Redox indicator dyes showed that growing E. coli, P. stutzeri, or L. lactis cells lowered the redox potential of the medium in a similar way as a reducing agent did. The lowered redox potential was presumably the key factor that stimulated ferrihydrite reduction by all three Geobacter species. The observed differences in anoxic non-reduced medium with ferric citrate versus ferrihydrite as electron acceptor indicated that reduction of these electron acceptors involved different cellular components or different biochemical strategies. Furthermore, it appears that redox-sensitive components are involved, and/or that gene expression of components needed for ferrihydrite reduction is controlled by the redox state.Dedicated to Prof. Dr. Dr. h.c. mult. Hans Günter Schlegel on the occasion of his 80th birthday.     

Variant genes and the spleen in Plasmodium vivax malaria

It is generally accepted that Plasmodium vivax, the most widely distributed human malaria, does not cytoadhere in the deep capillaries of inner organs and thus this malaria parasite must have evolved splenic evasion mechanism in addition to sequestration. The spleen is a uniquely adapted lymphoid organ whose central function is the selective clearance of cell and other particles from the blood, and microbes including malaria. Splenomegaly is a hallmark of malaria and no other disease seems to exacerbate this organ as this disease does. Besides this major selective clearance function however, the spleen is also an erythropoietic organ which, under stress conditions, can be responsible for close to 40% of the RBC populations. Data obtained in experimental infections of human patients with P. vivax showed that anaemia is associated with acute and chronic infections and it has been postulated that the continued parasitemia might have been sufficient to infect and destroy most circulating reticulocytes. We review here the basis of our current knowledge of variant genes in P. vivax and the structure and function of the spleen during malaria. Based on this data, we propose that P. vivax specifically adhere to barrier cells in the human spleen allowing the parasite to escape spleen-clearance while favouring the release of merozoites in an environment where reticulocytes, the predominant, if not exclusive, host cell of P. vivax, are stored before their release into circulation to compensate for the anaemia associated with vivax malaria.     

川南地区毛竹和林下植被芒箕细根分解特征

揭示竹林与其林下植被细根单独和混合分解特征,探讨竹林细根与其林下植被细根之间相互影响的潜在机制,为毛竹林林下植被的合理经营管理提供理论参考。采用原位分解袋法研究了四川长宁毛竹(Phyllostachys edulis)与林下植被芒箕(Dicranopteris pedata)细根分解和养分释放过程,试验周期为1年。结果表明(1)毛竹和芒箕细根初始化学组分有着明显差异,碳(C)含量、碳氮比(C/N)和碳磷比(C/P)毛竹显著高于芒箕(P0.05),而氮(N)含量、磷(P)含量和氮磷比(N/P)均芒箕高于毛竹(P0.05)。(2)毛竹和芒箕细根分解系数(k)分别为0.66±0.04和0.42±0.41,毛竹细根分解速率显著高于芒箕;土壤温度与分解速率呈显著正相关,是影响细根分解速率的关键环境因子。(3)毛竹和芒箕细根碳(C)、氮(N)、磷(P)养分释放均表现为净释放,毛竹细根碳(C)释放速率高于芒箕,但细根氮(N)和磷(P)释放率均低于芒箕。(4)混合分解的实测值和期望值对比结果表明毛竹和芒箕细根混合对分解速率和磷(P)元素的释放没有显著影响,但显著促进了碳(C)元素的释放,抑制了分解初期氮(N)元素的释放。毛竹与林下植被芒箕单独细根分解和养分释放特征均表现不同;细根混合分解速率无显著混合效应,但养分释放的混合效应表现出不同阶段性和不同方向(正或负),说明林下植被通过影响细根养分释放而影响竹林生态系统的养分循环。     

Glutathione peroxidase 2 in Saccharomyces cerevisiae is distributed in mitochondria and involved in sporulation

Gpx2, one of three glutathione peroxidase homologs (Gpx1, Gpx2, and Gpx3) in Saccharomyces cerevisiae, is an atypical 2-Cys peroxiredoxin that prefers to use thioredoxin as a reducing agent in vitro. Despite Gpx2 being an antioxidant, no obvious phenotype of gpx2Δ mutant cells in terms of oxidative stress has yet been found. To gain a clue as to Gpx2’s physiological function in vivo, here we identify its intracellular distribution. Gpx2 was found to exist in the cytoplasm and mitochondria. In mitochondria, Gpx2 was associated with the outer membrane of the cytoplasmic-side, as well as the inner membrane of the matrix-side. The redox state of the mitochondrial Gpx2 was regulated by Trx1 and Trx2 (cytoplasmic thioredoxin), and by Trx3 (mitochondrial matrix thioredoxin). In addition, we found that the disruption of GPX2 reduced the sporulation efficiency of diploid cells.     

Differences in the virulence of Heterorhabditis bacteriophora and Steinernema scarabaei to three white grub species: The relative contribution of the nematodes and their symbiotic bacteria

Because susceptibility of white grub species to entomopathogenic nematodes differs, we compared the virulence of Photorhabdus temperata and Xenorhabdus koppenhoeferi, the symbiotic bacteria of the nematodes Heterorhabditis bacteriophora and Steinernema scarabaei, respectively, to the three white grub species, Popillia japonica, Rhizotrogus majalis, and Cyclocephala borealis. Both bacteria were pathogenic to all three grub species even at 2 cells/grub. However, the median lethal dose at 48 h post injection and median lethal time at 20 cells/grub showed that P. temperata was more virulent than X. koppenhoeferi to C. borealis. Although H. bacteriophora is less pathogenic than S. scarabaei to R. majalis and P. japonica, their symbiotic bacteria did not differ in virulence against these two grub species, and they also showed similar growth patterns both in vitro and inside R. majalis larvae at 20 °C. We then tested the pathogenicity of oral- and intrahemocoel-introduced H. bacteriophora to R. majalis to determine whether nematodes are able to successfully vector the bacteria into the hemolymph. Hemocoel injected H. bacteriophora was pathogenic to R. majalis indicating successful bacterial release, but orally introduced H. bacteriophora were not. Dissection of grubs confirmed that the orally introduced H. bacteriophora were unable to penetrate into the hemolymph through the gut wall. We conclude that the low susceptibility of R. majalis to H. bacteriophora is not due to the symbiotic bacteria but rather to the nematode’s poor ability to penetrate through the gut wall and the cuticle to vector the bacteria into the hemolymph.