This paper discusses the biology, origin and molecular systematics (species identification and phylogenetic analysis) of nematodes. The taxonomy and systematics of Steinernematidae and Heterorhabditidae (morphology, taxonomy and phylogenetic relationships) are also discussed. Future prospects are mentioned.

Historically, the invertebrate pathogens of the genus Helicosporidium were considered to be either protozoa or fungi, but the taxonomic position of this group has not been considered since 1931. Recently, a Helicosporidium sp., isolated from the blackfly Simulium jonesi Stone & Snoddy (Diptera : Simuliidae), has been amplified in the heterologous host Helicoverpa zea. Genomic DNA has been extracted from gradient-purified cysts. The 18S, 28S and 5.8S regions of the Helicosporidium rDNA, as well as partial sequences of the actin and β-tubulin genes, were amplified by PCR and sequenced.Comparative analysis of these nucleotide sequences was performed using neighbour-joining and maximum-parsimony methods. All inferred phylogenetic trees placed Helicosporidium sp. among the green algae (Chlorophyta), and this association was supported by bootstrap and parsimony jackknife values. Phylogenetic analysis focused on the green algae depicted Helicosporidium sp. as a close relative of Prototheca wickerhamii and Prototheca zopfii (Chlorophyta, Trebouxiophyceae), two achlorophylous, pathogenic green algae. On the basis of this phylogenetic analysis, Helicosporidium sp. is clearly neither a protist nor a fungus, but appears to be the first described algal invertebrate pathogen. These conclusions lead us to propose the transfer of the genus Helicosporidium to Chlorophyta, Trebouxiophyceae.

Important findings from the second decade of the 21st century on the impact of environmental change on biological processes in the Antarctic were synthesised by 26 international experts. Ten key messages emerged that have stakeholderrelevance and/or a high impact for the scientific community. They address (i) altered biogeochemical cycles, (ii) ocean

Microbes are widely assumed to be capable of colonizing even the most challenging terrestrial surface environments on Earth given enough time. We would not expect to find surface soils uninhabited by microbes as soils typically harbor diverse microbial communities and viable microbes have been detected in soils exposed to even the most inhospitable conditions. However, if uninhabited soils do exist, we might expect to find them in Antarctica. We analyzed 204 ice‐free soils collected from across a remote valley in the Transantarctic Mountains (84–85°S, 174–177°W) and were able to identify a potential limit of microbial habitability. While most of the soils we tested contained diverse microbial communities, with fungi being particularly ubiquitous, microbes could not be detected in many of the driest, higher elevation soils—results that were confirmed using cultivation‐dependent, cultivation‐independent, and metabolic assays. While we cannot confirm that this subset of soils is completely sterile and devoid of microbial life, our results suggest that microbial life is severely restricted in the coldest, driest, and saltiest Antarctic soils. Constant exposure to these conditions for thousands of years has limited microbial communities so that their presence and activity is below detectable limits using a variety of standard methods. Such soils are unlikely to be unique to the studied region with this work supporting previous hypotheses that microbial habitability is constrained by near‐continuous exposure to cold, dry, and salty conditions, establishing the environmental conditions that limit microbial life in terrestrial surface soils.

Entornopathogenic Nematodes (Rhabditida Heterorhabditidae, Midwest ldvestock k m Res-h Labratmy, =A-AM. Deparbnent of ~t o m~l o g y , University af N e b m k Lincoln, NE 68s83 f i v h n . Entomot. 27(6): 1514-1519 (1998) A B S l ' M m The potential for entornopathogenic nematodas to cantml flies in cattle feedlots was determined by screening 40 s h i n s repmenting 8 species of H~~ Poinar and 5 species of S~~ Travassos for virulence toward 3rd-instar house flies (maggots), Musm dmmtfm L None of the 22 s h i n s of H & m d d d i h infecting maggots caused sipi6cant Ievels of mortality in a filter paper assay. Ten strains of S -inf&ed maggots, of which 7 strains (4 S. (Wdser), 2 S $ l W [Filipjev), and 1 5. w t a -k w i Nguyen & Smart) caused sign$& m o d i t y . Ten Hetemdddiitu strains and 10 Steinsrna~ strains successllly reproduced for 2 2 generations in rnagpts. N o diEemoce was obsened between 72-h survival of maggots and addt emergence. Six strains OF S t e i w m m m were selected for 10 generations on maggots and then compared with usselected lines. fio difference in pathogenicity between selected and unselmed lines was observed. Two s'trains of S. fib, SN and G'NK-36, and 2 of the best H&em&ddifi strains, H. boGgffiophom Poinm -GO and & mgfdis Poinar, Jackson & Idein HF-85 were tested h a fresh bovine manure subsbate. AU 4 h a i n s produced significaot fly mortality In the manure subhate, although the S f e l m strains had significantly lower L G values than did the HetaorfPabdihs 5pp. fie most promising strain, S . f e l f i m SH, gave LC, and U& vaitles of 4 and 82 infective juveniles per m~o t , respectively. These doses were equivalent to 2.7 nnd 55 infective juvenile per gram of manure and 5.1 and 104 infective jwedesper square centimeter of surface area Infcctive]uveniles capable of infectin$ greater wax moth larvae, Callrnia & h l b (L), survived in manure for up to 10 wk without hosts. KEY WORDS M m d m m d h , biol@cal control, feedlot, entmnopthogenic nematdes