Natural occurrence of entomopathogenic nematodes (rhabditida: steinernema, heterorhabditis) in the azores

A soil survey for entomopathogenic nematodes was conducted throughout the nine islands of the Azorean archipelago. Forty-six out of 1,180 samples (3.9%) were positive, with Heterorhabditis spp. isolated from 30 sites on six islands and Steinernema spp. isolated from 16 sites on three islands. São Miguel and Terceira Islands were positive for both genera, and Pico Island was positive only for Steinernema. Entomopathogenic nematodes were found from sea level up to 750 m. Seventy percent of the samples positive for Heterorhabditis were collected below 150 m, whereas 62.5% of the samples positive for Steinernema were collected above 300 m. Heterorhabditis was not isolated above 450 m. Steinernema was collected mostly in loamy-sand and sandy-loam soils with a pH below 6, whereas Heterorhabditis was mostly collected in sandy and loamy-sand soils with pH higher than 6. Steinernema and Heterorhabditis were found in cropland, orchards, and pastures, while Heterorhabditis was found also in woodland and native vegetation.

Pathogenicity caused by high virulent and low virulent strains of Steinernema carpocapsae to Galleria mellonella

Steinernema carpocapsae is an entomopathogenic nematode associated with a symbiotic bacterium, Xenorhabdus nematophilus. Both components of the complex participate in a pathogenic process in insects. This has raised two questions: how much does each one participate, and what mechanisms are involved? In this paper we compare the virulence of two strains of S. carpocapsae: a high virulent strain (Breton) and a low virulent strain (Az27), both of which are free of symbiotic bacteria. Breton and Az27 strains each one have similar ability to invade Galleria mellonella with median infectious times of 3.9 and 3.2 h, respectively. However, the LD(50) of the Breton and Az27 strains are 48.6 and 894.5 infective juveniles per insect, respectively. Breton strain takes 38 h to kill 100% of exposed insects, whereas Az27 takes three times longer. The lethal time of the low virulent strain in G. mellonella larvae is highly dependent on the number of nematodes which have penetrated the hemocelium, whereas it is not on the high virulent strain. Hemolymph patterns in SDS-PAGE of insects parasitized by the high virulent strain showed important differences in respect to the low virulent strain and control. Secretion/excretion products of the high virulent strain have important proteolytic activity as well as alpha-mannosidase and alpha-fucosidase activities, whereas, in secretion/excretion products of the avirulent strain, proteolytic activity was lower and alpha-mannosidase and alpha-fucosidase activities were undetected.

Gnotobiological study of infective juveniles and symbionts of Steinernema scapterisci: A model to clarify the concept of the natural occurrence of monoxenic associations in entomopathogenic nematodes

Gnotobiology of Steinernema scapterisci and bacteriological study of its symbiont confirmed that this nematode harbors a symbiotic species of Xenorhabdus, as do other Steinermena species. Based on phenotypic and 16S rDNA data, this Xenorhabdus strain UY61 could be distinguished from other Xenorhabdus species. Bacteria reported previously as being associated with this nematode and belonging to several other genera were probably contaminating bacteria located in the intercuticular space of the infective juveniles (IJs). These bacteria were detrimental to nematode reproduction in Galleria mellonella. Axenic S. scapterisci and its symbiont Xenorhabdus strain UY61 alone were not pathogenic to G. mellonella. The combination of both partners reestablished the pathogenicity of the complex toward G. mellonella. This combination also gave the best yields of IJs when produced in this insect and in vitro production on artificial diet.

A species-specific satellite DNA from the entomopathogenic nematode Heterorhabditis indicus

An AluI satellite DNA family has been cloned from the entomopathogenic nematode Heterorhabditis indicus. This repeated sequence appears to be an unusually abundant satellite DNA, since it constitutes about 45% of the H. indicus genome. The consensus sequence is 174 nucleotides long and has an A + T content of 56%, with the presence of direct and inverted repeat clusters. DNA sequence data reveal that monomers are quite homogeneous. Such homogeneity suggests that some mechanism is acting to maintain the homogeneity of this satellite DNA, despite its abundance, or that this repeated sequence could have appeared recently in the genome of H. indicus. Hybridization analysis of genomic DNAs from different Heterorhabditis species shows that this satellite DNA sequence is specific to the H. indicus genome. Considering the species specificity and the high copy number of this AluI satellite DNA sequence, it could provide a rapid and powerful tool for identifying H. indicus strains.

Molecular characterization of two species-specific tandemly repeated DNAs from entomopathogenic nematodes Steinernema and Heterorhabditis (Nematoda:Rhabditida)

Two AluI tandemly repeated DNAs were cloned from two entomopathogenic nematodes: the first one from Steinernema glaseri and the second one from Heterorhabditis bacteriophora. The monomeric units of these two satellite DNAs have a repeat length of 174 and 168 bp, respectively. These AluI repeated element families appear to constitute 5.5% of the S. glaseri genome and 5% of the H. bacteriophora genome. Their A + T contents were estimated at 55% and 57%. Moreover, the monomers of these two families are quite homogeneous in sequence, showing, on average, 3.9% and 2.7% divergence from their respective consensus sequence. These results suggest that some mechanism is acting to maintain the homogeneity of these repeated DNAs despite their abundance. We have also shown that these two DNA families are species-specific and therefore could be used for the identification of Steinernema and Heterorhabditis entomopathogenic nematode species.

Use of species-specific satellite DNAs as diagnostic probes in the identification of Steinernematidae and Heterorhabditidae entomopathogenic nematodes

Three satellite DNAs previously isolated from the entomopathogenic nematodes Steinernema carpocapsae, Heterorhabditis bacteriophora and Heterorhabditis indicus give hybridization signals only with the S. carpocapsae, H. bacteriophora and H. indicus populations tested, indicating that these satellite sequences are species-specific. Because of their reiteration and their variabilities, we have shown that these sequences are able to discriminate at the interspecific level between the Steinernema and Heterorhabditis species, but also at the intraspecific level between S. carpocapsae strains. Furthermore, in simple squashed nematode experiments, we are able to unambiguously identify S. carpocapsae, H. bacteriophora and H. indicus populations. This last procedure is effective even on a single infective juvenile, with the main advantage that it avoids time-consuming DNA extractions.

Characterization of a species-specific satellite DNA from the entomopathogenic nematode Steinernema carpocapsae

An HaeIII satellite DNA family has been cloned from the entomopathogenic nematode Steinernema carpocapsae. This repeated sequence appears to be an unusually abundant satellite DNA, since it constitutes about 62% of the S. carpocapsae genome. The nucleotide sequences of 13 monomers have been determined. This satellite DNA family is represented by two sub-families: one with monomeric units of 170 bp and the other with monomeric units of 182 bp. These monomers are quite homogeneous in sequence, showing an average intermonomer variability of 6% from the consensus sequence. These results suggest that some homogenizing mechanism is acting to maintain the homogeneity of this satellite DNA. After hybridization with the genomic DNA of several other Steinernema species, this DNA sequence appears to be specific to the S. carpocapsae genome. Therefore, the species specificity and the high copy number of the HaeIII satellite DNA sequence should provide a rapid and powerful tool which could contribute to the identification of Steinernema species.

Effectiveness of Steinernema spp. and Heterorhabditis bacteriophora against Popillia japonica in the Azores

Steinernema carpocapsae (Breton strain), S. glaseri, and Heterorhabditis bacteriophora were evaluated for their potential to control immature stages of the Japanese beetle, Popillia japonica, on Terceira Island (the Azores). In bioassays carried out at temperatures higher than 15 C, S. glaseri and H. bacteriophora caused 100% mortality of larvae, whereas S. carpocapsae caused 56% larval mortality. At temperatures slightly below 15 C, only S. glaseri remained effective. In field plots, in September, S. glaseri and S. carpocapsae reduced larval populations by 91% and 44%, respectively, when applied at the rate of 10 nematodes/m(2). In April, S. glaseri caused 31% reduction in numbers of larvae, but S. carpocapsae was ineffective. In colder months (November-February) neither steinernematids nor H. bacteriophora reduced larval populations. Increasing the application rate from 10 to 5 x 10 infective stage S. glaseri per m(2) increased efficacy from 63% to 79% mortality.

Noctuidonema daptria, n. sp. (Nematoda: Aphelenchoididae), an Ectoparasite of the Moth Lesmone porcia (Stoll)

Described and illustrated for the first time is a bisexual aphelenchoidid ectoparasitic nematode found on a noctuid male moth in Guadeloupe, West Indies. Sexes are polymorphic, having in common an elongated stylet of 53-69 mum with well-developed basal knobs and double set of protractors, excretory pore near head end, multiple rows of germ cells, and a mucronate tail terminus. The male is particularly distinctive in having a low, smooth head, spicules 38-49 mum long with a tubular rostrum and a ventral arm well separated from the dorsal, an external cloacal cylinder, and a pre- and postanal pair of genital papillae. Distinctive for the female are a unique, muldnucleate uterine gland complex, lack of a functional rectum and anus, and, by marked contrast to the male, a high, hemispherical head marked by six annules and a large uninucleate renette cell.

[Empidomermis riouxi n. sp. (Nematoda, Mermithidae). (author's transl)]

Empidomermis riouxi n. sp. is described from Aedes (Ochlerotatus) detritus, in Camargue. The species differs from E. cozi, which is the only other species of the genus, by having a sligtly larger size and a very little pronounced cephalic constriction. Males differ also from those of E. cozi by the number and disposition of the caudal papillae. The postparasitic larvae escape from adult mosquitoes, rarely from pupae. In laboratory conditions, the nematodes enter the moist sand in the bottom of Petri dishes where, after about 20 days, they molt, mate and oviposit. All the larval stages of A. detritus can be found infected. The presence of parasites induce the arrest of the ovarian development of the females and inhibits the mating activity of males. The rate of parasitism is very high and its fluctuations seem closely related to the host life cycle.

[Neoparasitylenchus megabothridis n. sp. (Tylenchida: Allantonematidae) parasite of Megabothris tubidus (Siphonaptera: Ceratophyllidae); observations on fleas tylenchides in the S.W. of Europa (author's transl)]

A number of nematodes (Tylenchida, Allantonematidae) were observed in 11 species of Siphonaptera from the South-West of Europe. The fleas belong of 4 differents families (Pulicidae, Vermipsyllidae,Hystrichopsyllidae, Ceratophyllidae). Neoparasitylenchus megabothridis n. sp., parasite of the flea Megabothris turbidus (Rothschild, 1909), is described and the life cycle given. It shows little pathogenicity to tis host. Psyllotylenchus sp. parasite of Nosopsyllus fasciatus (Bosc, 1801), appears to be a teratogenic and causes a feminisation of parasitised males and a masculinisation of females. A generic determination cannot be made with any certainty in the material collected from others fleas.