Nathan Cobb, as the father figure of the Society of Nematologists, set an example to later generations of nematologists in his studies of nematode biology. In the 50 years of the Society’s existence nematological research has greatly expanded that knowledge base. Opportunities over the next 50 years are boundless in view of advancing technologies and emerging challenges, and this leads to speculation as to what future nematological research advances will enhance peoples’ quality of life.
behavior; biocontrol; chemosensory; ecology; entomopathogenic nematodes; genomics; marine nematology; molecular technology; nematicides; non-tariff barriers; plant resistance; taxonomy; transgenic plants
The ability of Steinernema feltiae or Heterorhabditis bacteriophora infective juveniles (IJ), when applied to the soil surface, to infect a Galleria mellonella larva at the base of a soil-filled cup (276 cm³) was evaluated in the presence and absence of 100 larvae of a non-target insect, the aphid midge Aphidoletes aphidimyza, near the soil surface. In all four trials with either S. feltiae or H. bacteriophora, A. aphidimyza presence did not affect the number of IJ finding and infecting a G. mellonella larva. Steinernema feltiae and H. bacteriophora IJ movement (as measured by the percentage of IJ aggregating on either side of an experimental arena) in the presence of one or many A. aphidimyza larvae was evaluated in agar- and soil-filled petri dishes, respectively. Infective juvenile movement in the presence of A. aphidimyza did not differ from random, indicating that IJ were not attracted to A. aphidimyza. It is suggested, therefore, that A. aphidimyza does not reduce IJ efficacy when these two forms of biological control agent are present together in a field situation even though it is known that A. aphidimyza is susceptible to IJ of these species.
Aphidoletes aphidimyza; entomopathogenic nematodes; Galleria mellonella; Heterorhabditis bacteriophora; host finding; nontarget; Steinernema feltiae
A small-colony variant (Vsm) of the primary form (Vp) of Photorhabdus luminescens MD from in vitro and in vivo cultures is described. Unlike the primary form, Vp, the Vsm variant is not the preferred diet of its nematode symbiont, a Heterorhabditis sp., does not support development and reproduction of the nematode, and is less pathogenic than Vp to Galleria mellonella larvae. Vsm cells were carried by 25% of infective juveniles, but they comprised a very low percentage (∼0.4%) of the total cells carried by the juvenile. In vitro subculture and in vivo injection into the larvae with either Vp or Vsm always produced a mixture of both Vp and Vsm. In nematode-bacterium-infected G. mellonella larvae, the Vp population in the hemocoel was high (4 × 109 to 5 × 109 CFU/g of wet insect tissue) at 24 h after infection, decreased about 10-fold by 48 h, and then regained a high level at day 5 before decreasing at day 7 and then remaining relatively constant through day 15 postinfection. The Vsm population, under the same conditions as those of Vp, increased gradually to a high level (9 × 108 CFU/g of wet insect tissue) at day 5 postinfection and then declined gradually through day 15.
Xenorhabdus nematophilus subsp. dutki, an entomopathogenic bacterium, is vectored by steinernematid nematodes into insects, where it produces broad-spectrum antibiotics. The use of the nematode-bacterium complex against soil-dwelling pest insects could introduce antibiotics into the soil via the dead insect fragments during the emergence phase of the nematodes. Studies on the stability and activities of these antibiotics produced in the insect Galleria mellonella may contribute to assessing the possible impact of antibiotics on soil bacteria. Two isolates of X. nematophilus subsp. dutki (isolates GI and SFU) produced xenocoumacins 1 and 2 in cadavers of G. mellonella larvae in a 1:1 ratio. Total xenocoumacin 1 and 2 production was 800 ng/200 mg (wet weight) of insect tissue for the GI isolate. Antibiotic activity of water extracts from insects that had been infected with X. nematophilus was stable at 60°C for 1 h and after repeated freeze-thaw cycles. The antibiotic titer of extracts held at 27°C declined by day 10. The spectrum of bacterial species killed by antibiotics produced in insect cadavers varied with the isolate of X. nematophilus. Levels of antibiotic activity were greater in vivo than in tryptic soy broth, which may represent a nutrient effect. The bacterial isolate, culture condition, and presence of nematodes influenced the total antibiotic production in vivo. However, the levels of activity were not correlated with bacterial levels in the different growth environments. Insect cadavers with antibiotic activity transiently lowered the numbers of the bacteria in the soil, the extent of decline varying with the strain of X. nematophilus and the time of sampling.
A survey was done in the summer months along the Alaska Highway, in other parts of British Columbia, in northern Alberta, and in the Yukon Territory for steinernematid and heterorhabditid nematodes occurring in the top 10 cm of soil. Steinernema feltiae and Steinernema spp. were found at 18 and Heterorhabditis megidis at 7 sites of 125 sampled. Most nematodes were found where visible insect infestation occurred and where human influence on the habitat was substantial (e.g., agricultural, forested and bush-hedgerow habitats); none was found in grassland or virgin forests. Heterorhabditis megidis occurred in only the southern, warmer, drier region of British Columbia. In the laboratory some steinernematid isolates and H. megidis killed Galleria mellonella larvae at 13 and 22 C, whereas some isolates of Steinernema killed the larvae at only 13 C. Steinernema spp. from three high altitude sites with low, average July temperatures (13-14 C) are cold-active in that they produced infective juveniles at 13 C and killed G. mellonella at 6 C.
biological control; entomopathogenic nematode; Heterorhabditidae; low-temperature activity; nematode; Steinernenaatidae; survey; temperature
This study examined the ribosomal cistron of Ditylenchus destructor, D. myceliophagus and seven host races of D. dipsaci from different geographic locations. The three species showed restriction fragment length polymorphisms (RFLPs) in the ribosomal cistron, the 18S rDNA gene, and the ribosomal internal transcribed spacer (ITS). Southern blot analysis with a 7.5-kb ribosomal cistron probe differentiated the five host races of D. dipsaci examined. Polymerase chain reaction (PCR) amplification of the ITS, followed by digestion with some restriction endonucleases (but not others), produced restriction fragments diagnostic of the giant race. Because the PCR product from D. myceliophagus and the host races of D. dipsaci was about 900 base pairs and the ITS size in D. destructor populations was 1,200 base pairs, mixtures of populations could be detected by PCR amplification. ITS fragments differentiated between D. dipsaci and Aphelenchoides rhyntium in mixed populations. This study establishes the feasibility of differentiation of the host races of D. dipsaci by probing Southern blots with the whole ribosomal cistron.
Ditylenchus destructor; D. dipsaci; D. myceliophagus; DNA; host race; internal transcribed spacer; nematode; polymerase chain reaction; restriction fragment length polymorphism; ribosomal DNA; sibling species
Identification of closely related nematode species or races can be very difficult when diagnostic characters are plastic and overlapping. In this study we describe the use of polymerase chain reaction technology and direct DNA sequencing on 19 populations of Bursaphelenchus spp. to help understand their taxonomic relationships. The 5' end of the heat shock 70A gene from Caenorhabditis elegans was used as the target DNA sequence because it contains both coding and non-coding regions. The results indicate that the 19 populations could be divided into five types within B. xylophilus and four types within B. mucronatus. On a larger scale, the data revealed three distinct groups, representing B. xylophilus from North America and Japan, B. mucronatus from Japan, and "B. mucronatus" from Europe. There is sufficient difference between the European and Japanese "B. mucronatus" groups to warrant their consideration as separate species.
Bursaphelenchus mucmnatus; B. xylophilus; Caenorhabditis elegans; DNA; gene; heat shock; molecular phylogeny; nematode; pinewood nematode; polymerase chain reaction; species complex; taxonomy
Heterorhabditis heliothidis; Steinernema feltiae; Mexican strain; DD136 strain; temperature acclimation; prolonged culture; virulence
Nematode parasites and associates of four bark beetle species in British Columbia were surveyed. Bursaphelenchus varicauda n.sp., Ektaphelenchus macrostylus, Panagrolaimus dentatus, and Cryptaphelenchus latus were found associated with Dendroctonus pseudotsugae. Parasitorhabditis obtusa was found in the gut and Contortylenchus reversus in the hemocoel of both D. pseudotsugae and D. rufipennis. The latter also had hemocoel infections of Sphaerulariopsis dendroetoni, which were not found concomitant with C. reversus infections. Contortylenchus brevicomi occurred in the hemocoel of D. brevicomis. The first report of a tylenchid larva parasitizing Trypodendron lineatum in North America is presented. Bursaphelenchus varicauda n.sp. was obtained from the gallery frass of D. pseudotsugae. It resembles B. corneolus and B. bestiolus but differs from the former species in female tail shape, the position of the excretory pore, spicule shape, and position of the male caudal papillae, and from the latter species in spicule shape and in the length of the esophagus and postuterine sac.
taxonomy; new species; entomogenous nematodes; Douglas-fir beetle; bark beetle
Schistocerca gregaria nymphs and adults of both sexes were infected with eggs of Mermis nigrescens. Mermithid larvae grew more slowly in nymphal hosts, and emerging larvae were smaller than those from adult hosts. The longer the larvae remained in the host, the greater their size. Those developing in adult female hosts were longest. Single mermithid larvae that were transferred to a second host continued to grow and were significantly longer at emergence than larvae that developed solely in one host. In adult hosts that were infected with 40-300 M. nigrescens eggs, the percentage of mermithids that became males was strongly dependent on host weight at infective doses of 90 eggs or more. Results are discussed in relation to nutrient stress on the larvae and its importance in developing in vitro culture techniques.
sex ratios; parasite burden; Mermis nigrescens; Schistocerca gregaria; nutrient stress; larval development
A review of the development of entomophilic nematology and a commentary on the potential of entomophilic nematodes in controlling insect pests. The paper considers some of the major contributions to our knowledge of entomophilic nematology; factors involved in insect pest management and how they are applicable to the use of nematodes; nematodes which are most promising as biological control agents; and problems to be solved to facilitate the use of entomophilic nematodes in insect management.
Mermis nigrescens; Neoaplectana spp.; Romanomermis culicivorax; Deladenus siricidicola; Tetradonema plicans
Contortylenchus barberus is synonymized with C. brevicomi because their original separation was based on minor morphometric variations that are considered here to be intraspecific rather than interspeciflc. The ranges of body length and body width in measured specimens of C. brevicomi encompass those of the original description of C. brevicomi and C. barberus. The presence or absence of the caudal mucro is considered not a valid criterion for species differentiation. Several of the morphometric details of the two species overlap and thus are not considered suitable for species differentiation. Such variation may be due to stresses of the host-parasite relationship. The respective hosts of the two nematodes, Dendroctonus brevicomis and D. barberi, have been synonymized into the former species. The description of the larval stages of C. brevicomi is presented.