Natural enemy impacts on Bemisia tabaci (MEAM1) dominate plant quality effects in the cotton system

1. Plant quality (bottom‐up effects) and natural enemies (top‐down effects) affect herbivore performance. Furthermore, plant quality can also influence the impact of natural enemies. 2. Lower plant quality through reduced irrigation increased the abundance of the cryptic species from the Bemisia tabaci complex [hereafter B. tabaci Middle East Asia Minor 1 (MEAM1)], but not its natural enemies on cotton. It was therefore predicted that lower plant quality would diminish the impact of natural enemies in regulating this herbivore. 3. Over three cotton seasons, plant quality was manipulated via differential irrigation and natural enemy abundance with insecticides. Life tables were used to evaluate the impact of these factors on mortality of immature B. tabaci (MEAM1) over nine generations. 4. Mortality of B. tabaci (MEAM1) was consistently affected by natural enemies but not by plant quality. This pattern was driven by high levels of sucking predation, which was the primary (key) factor associated with changes in immature mortality across all irrigation and natural enemy treatments. Dislodgement (chewing predation and weather) and parasitism contributed as key factors in some cases. Analyses also showed that elimination of sucking predation and dislodgement would have the greatest effect on overall mortality. 5. The top‐down effects of natural enemies had dominant effects on populations of B. tabaci (MEAM1) relative to the bottom‐up effects of plant quality. Effects were primarily due to native generalist arthropod predators and not more host‐specific aphelinid parasitoids. The findings of this study demonstrate the important role of arthropod predators in population suppression and validate the importance of conservation biological control in this system for effective pest control.     

<Emphasis Type="Italic">In vitro</Emphasis> Relationship of SV40 Tumour-specific Surface Antigen to other SV40 Antigens

WE have previously described a rapid and quantitative cytotoxic assay in which target cells labelled with⁵¹Cr are used to identify a tumour-specific surface (TSS) antigen expressed by different lines of mouse cells transformed by SV40. We have now investigated the relationship between the activity of this antigen and the virus-specific surface (S) antigen, associated with SV40 transformed hamster cells².     

Importance of fire in influencing the occurrence of snakes in an upland region of arid Australia

In arid Australia, changes to historic fire regimes may now produce more large‐scale wildfire events. The impacts of these fires on fauna communities are poorly known. We sought to test the impacts of fire on the occurrence of two arid‐zone snake species, the desert death adder (Acanthophis pyrrhus) and monk snake (Parasuta monachus), specialist inhabitants of hummock grassland and mulga shrubland, respectively. We also examined the influence of fire on the occurrence of a habitat generalist, the sympatric Stimson's python (Antaresia stimsoni). Under an Information‐Theoretic framework we modelled the occurrence of each species with a range of habitat variables, including fire history, using logistic regression. As predicted, the two habitat specialists were more likely to be encountered at locations that had a lower percentage of surrounding area burnt in the most recent wildfires (2002), while fire variables failed to predict the occurrence of the habitat generalist. Acanthophis pyrrhus, already predisposed to endangerment through a suite of life‐history characteristics, may be at increased risk through accidental and deliberate burning and fragmentation of old‐growth hummock grasslands. We stress the importance of prescribed burning and natural fire breaks in maintaining areas of old‐growth hummock grassland across the landscape.     

Macromolecules in brachiopod shells: characterization and diagenesis

An immunological investigation was conducted of soluble intra-crystalline macromolecules isolated from living and fossil brachiopod shells, which had previously been used for an immunologically based study of phylogeny (serotaxonomy). The soluble intra-crystalline macromolecules comprised 0.03% by weight of the extant shell material. Bulk analysis and gel electrophoresis indicated that the organic material is predominantly glycoprotein, and contains up to 30% by weight carbohydrate. Treatment of the macromolecules with periodate and proteinase K revealed that antibodies were raised predominantly against the carbohydrate moieties. Using a specially adapted dot blot immunobinding assay (DIBA) the decay in immunological signal over geological time was determined. Pleistocene shells have lost between 99 and 99.9% of immunological reactivity, and original antigenic determinants form a declining proportion of total organic matter. It is suggested that condensation reactions between amino acids and sugars account for the rapid destruction of determinants; this has important implications for the direction of future studies on fossil macromolecules. □ Serotaxonomy, biomolecular palaeontology, glycoproteins, melanoidins, brachiopods.     

Deeply divergent mitochondrial lineages reveal patterns of local endemism in chironomids of the Australian Wet Tropics

The Wet Tropics bioregion of north‐eastern Australia has been subject to extensive fluctuations in climate throughout the late Pliocene and Pleistocene. Cycles of rainforest contraction and expansion of dry sclerophyll forest associated with such climatic fluctuations are postulated to have played a major role in driving geographical endemism in terrestrial rainforest taxa. Consequences for the distributions of aquatic organisms, however, are poorly understood. The Australian non‐biting midge species Echinocladius martini Cranston (Diptera: Chironomidae), although restricted to cool, well‐forested freshwater streams, has been considered to be able to disperse among populations located in isolated rainforest pockets during periods of sclerophyllous forest expansion, potentially limiting the effect of climatic fluctuations on patterns of endemism. In this study, mitochondrial COI and 16S data were analysed for E. martini collected from eight sites spanning the Wet Tropics bioregion to assess the scale and extent of phylogeographic structure. Analyses of genetic structure showed several highly divergent cryptic lineages with restricted geographical distributions. Within one of the identified lineages, strong genetic structure implied that dispersal among proximate (<1 km apart) streams was extremely restricted. The results suggest that vicariant processes, most likely due to the systemic drying of the Australian continent during the Plio‐Pleistocene, might have fragmented historical E. martini populations and, hence, promoted divergence in allopatry.