How do local differences in saltmarsh ecology influence disease vector mosquito populations?

Saltmarsh breeding mosquitoes are an important source of vectors for arboviral transmission. In southern Australia, the most prominent vector borne disease, Ross River virus (Togaviridae: Alphavirus) (RRV), is transmitted by the saltmarsh mosquito (Diptera: Culicidae) Aedes camptorhynchus (Thomson). However, the factors driving the abundance of this mosquito within and among saltmarshes are poorly understood. To predict the abundance of this mosquito within saltmarshes, the environmental conditions and aquatic invertebrate ecology of three temperate saltmarshes habitats were monitored over two seasons. Up to 44% of first-instar mosquito numbers and 21% of pupal numbers were accounted for by environmental variables. Samphire vegetation cover was a common predictor of first-instar numbers across sites although, between saltmarshes, aquatic factors such as high salinity, temperatures less than 22 °C and water body volume were important predictors. The identified predictors of pupal numbers were more variable and included high tides, waterbody volume and alkalinity. The composition of invertebrate functional feeding groups differed between saltmarshes and showed that an increased diversity led to fewer mosquitoes. It was evident that apparently similar saltmarshes can vary markedly in invertebrate assemblages, water availability and conditions through tidal inundations, rainfall or waterbody permanency. The present study advances insight into predictors of vector mosquito numbers that drive the risk of RRV outbreaks.

Genetic and host-associated differentiation within Thrips tabaci Lindeman (Thysanoptera: Thripidae) and its links to Tomato spotted wilt virus-vector competence.

Of eight thelytokous populations of onion thrips (Thrips tabaci) collected from potato (three populations), onion (four) or Chrysanthemum (one) hosts from various regions of Australia, only those from potato were capable of transmitting Tomato spotted wilt virus (TSWV) in controlled transmission experiments. Genetic differentiation of seven of these eight populations, and nine others not tested for TSWV vector competence, was examined by comparison of the DNA sequences of mitochondrial cytochrome oxidase subunit 1 (COI) gene. All Australian populations of T. tabaci grouped within the European 'L2' clade of Brunner et al. (2004). Within this clade the seven populations from potato, the three from onion, and the four from other hosts (Chrysanthemum, Impatiens, lucerne, blackberry nightshade) clustered as three distinct sub-groupings characterised by source host. Geographical source of thrips populations had no influence on genetic diversity. These results link genetic differentiation of thelytokous T. tabaci to source host and to TSWV vector capacity for the first time.

Environmental drivers of Ross River virus in southeastern Tasmania, Australia: towards strengthening public health interventions.

In Australia, Ross River virus (RRV) is predominantly identified and managed through passive health surveillance. Here, the proactive use of environmental datasets to improve community-scale public health interventions in southeastern Tasmania is explored. Known environmental drivers (temperature, rainfall, tide) of the RRV vector Aedes camptorhynchus are analysed against cumulative case records for five adjacent local government areas (LGAs) from 1993 to 2009. Allowing for a 0- to 3-month lag period, temperature was the most significant driver of RRV cases at 1-month lag, contributing to a 23·2% increase in cases above the long-term case average. The potential for RRV to become an emerging public health issue in Tasmania due to projected climate changes is discussed. Moreover, practical outputs from this research are proposed including the development of an early warning system for local councils to implement preventative measures, such as public outreach and mosquito spray programmes.

Is the elusive Gymnothorax polyuranodon really a freshwater moray?

Analysis of 36 records of the rarely encountered moray Gymnothorax polyuranodon indicate that juveniles and adults inhabit fresh and mildly brackish habitats (salinity < 5) in streams of the Australian Wet Tropics Eighty-one per cent of these records were from freshwater streams and collectively demonstrate that this species inhabits fresh water throughout all seasons. A survey of fish researchers, each with at least 100 h of field experience in Australia's Wet Tropics, revealed that 33% of researchers working in fresh waters (nine of 27 researchers) had encountered the species and 15% of researchers with substantial experience working in estuaries (two of 13 researchers) had encountered the species. The species was not sampled or observed in the nearshore marine environment. The only record of an elver of this species was, however, found in an estuary at a salinity of 33·4. This preliminary evidence suggests adult G. polyuranodon occupy freshwater habitats, but further research is required to understand the complete life cycle, including movements, habitat use and reproductive ecology of the species.

Invasion success of the bumblebee, Bombus terrestris, despite a drastic genetic bottleneck.

In early 1992, the European bumblebee, Bombus terrestris, was first seen in Tasmania and currently has spread to most of the island. Here, we report on the genetic structure, using micro-satellites, of the invading population from samples collected in the years 1998-2000, a few years after the first sighting of the species in its new area. The data show that the Tasmanian population has a very low genetic diversity, with less than half of the allelic richness (Richness=2.89 alleles; H(exp)=0.591) and lower levels of heterozygosity as compared to populations in New Zealand (4.24 alleles; H(exp)=0.729) and Europe (5.08 alleles; H(exp)=0.826). In addition, the genetic data suggest that the invasion must have happened once, probably around late 1991, and was the result of very few, perhaps only two, individuals arriving in Tasmania. Furthermore, these founders came from the New Zealand population. Today, the population in the south of Tasmania seems to act as a source population from which individuals migrate into other parts of the state. A similar source-sink structure seems also the case for New Zealand. The data show that B. terrestris is a highly invasive species capable of establishing itself even after a dramatic genetic bottleneck. B. terrestris may be an invasive species due to the haplo-diploid sex determination system, which exposes recessive, deleterious mutations to selection. Offspring of such purged lines may then be able to tolerate high levels of inbreeding.

Blowfly succession from possum (Trichosurus vulpecula) carrion in a sheep-farming zone.

The significance of brushtail possum, Trichosurus vulpecula Kerr (Diprotodontia: Phalangeridae) carcasses to the succession and production of Diptera species and its relevance to fly strike management in Tasmania, Australia was examined. Calliphora stygia (Fabricius), Lucilia sericata (Meigen) and Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae) were found to be the most abundant and Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae) always the least abundant (< 1%) of the putative primary fly invading species to emerge. Carcasses that were left for up to 15 days in the field before being exposed to flies for 2 days also acted as breeding sites for large numbers of all primary fly species, with the exception of L. cuprina. Ordination analysis revealed no relationship between possum carcasses according to their length of exposure but did show significant negative associations between the number of putative secondary invaders (Chrysomya rufifacies (Macquart) (Diptera: Calliphoridae), Chrysomya varipes (Macquart) (Diptera: Calliphoridae) and putative tertiary flies (Hydrotaea rostrata Robineau-Desvoidy (Diptera: Muscidae)) to the number of C. vicina or C. stygia to emerge. There was enormous variability in the numbers of secondary/tertiary fly species to emerge from carcasses (0-11 450) that negatively correlated with the proportion of all flies to emerge that were primary, and with the mean size of adult L. sericata. Although carcass temperatures, especially those with a large larval population, were elevated, this did not appear to result in significant pre-adult fly mortality. The most important primary fly strike species L. cuprina was only found in insignificant numbers, whereas three other members of the fly strike fauna C. stygia, L. sericata and Ch. rufifacies did use possum carrion as an important breeding resource, but left implications for fly strike management inconclusive.

Geographical variation, population structure and gene flow between populations of Chrysophtharta agricola (Coleoptera: Chrysomelidae), a pest of Australian eucalypt plantations.

Chrysophtharta agricola (Chapuis) is a pest of commercial eucalypt plantations in Tasmania and Victoria. Vagility of pest populations may result in difficulty predicting temporal and spatial pest outbreaks, and influence genetic resistance to chemical control. Gene flow in this pest species was estimated to assess predictability of attack, the potential efficacy of natural enemies, and the likelihood of resistance build-up. Ten geographic populations of C. agricola (six from Tasmania, one from the Australian Capital Territory, one from New South Wales and two from Victoria) were examined for genetic variation and gene flow using cellulose acetate allozyme electrophoresis. Six enzyme systems (PGI, PGD, PGM, IDH, HEX and MPI) were consistently polymorphic and scorable and were used to quantify estimated gene flow between populations. FST values and analysis of molecular variance indicated that gene flow was restricted between populations. Chrysophtharta agricola exhibited high levels of heterozygosity, probably because of high allelic diversity, and because all loci examined were polymorphic. The southern-most population was the most genetically different to other Tasmanian populations, and may also have been the most recently colonized. Limited gene flow implies that outbreaks of C. agricola should be spatially predictable and populations susceptible to control by natural enemies. Our results also imply that genetic resistance to chemical control may occur under frequent application of insecticide. However, testing population movement between plantations and native forest also needs to be conducted to assess gene flow between forest types.

Intraplant distribution of Acalitus essigi (Acari: Eriophyoidea) on blackberries (Rubus fruticosus agg.).

Specialised phytophagous arthropods often display high levels of specificity to particular sites on their host plant. In this paper we examine the occupation of microhabitats and aggregation patterns of the eriophyoid mite, Acalitus essigi (Hassan), on its host plant, European blackberry (Rubus fruticosus L. aggregate), a plant that undergoes significant seasonal changes in its morphology. A. essigi was found to be a refuge inhabiting species. It resided in bud and leaf axil microhabitats on both primocanes and fructocanes and also occupied berry and bract microhabitats on fructocanes. Population fluctuations within the different microhabitats were evident across seasons. From summer to winter, populations significantly declined in bract and leaf axil microhabitats, but significantly increased within bud microhabitats where overwintering took place as slowly reproducing colonies. Live fruit and young shoots were also identified as overwintering sites. A. essigi populations displayed an aggregated distribution both within and between individual blackberry canes. Within primocanes A. essigi were aggregated in the lower 20% of cane length. On fructocanes aggregation of A. essigi was in the lower 20% and especially in the upper 20% of cane length. In spring A. essigi was confirmed to emerge from bud overwintering sites and colonise shoots mainly in the lower third of the previous season's primocanes, suggesting limited dispersal away from overwintering sites. It is proposed that biotic factors such as tissue age, microhabitat morphology and limited ambulatory dispersal capabilities are responsible for the aggregation pattems of this mite.

Influence of Environmental Factors and Medium Composition on Vibrio gazogenes Growth and Prodigiosin Production.

Vibrio gazogenes ATCC 29988 growth and prodigiosin synthesis were studied in batch culture on complex and defined media and in chemostat cultures on defined medium. In batch culture on complex medium, a maximum growth rate of 0.75 h and a maximum prodigiosin concentration of 80 ng of prodigiosin . mg of cell protein were observed. In batch culture on defined medium, maximum growth rates were lower (maximum growth rate, 0.40 h), and maximum prodigiosin concentrations were higher (1,500 ng . mg of protein). In batch culture on either complex or defined medium, growth was characterized by a period of logarithmic growth followed by a period of linear growth; on either medium, prodigiosin biosynthesis was maximum during linear growth. In batch culture on defined medium, the initial concentration of glucose optimal for growth and pigment production was 3.0%; higher levels of glucose suppressed synthesis of the pigment. V. gazogenes had an absolute requirement for Na; optimal growth occurred in the presence of 100 mM NaCl. Increases in the concentration of Na up to 600 mM resulted in further increases in the concentration of pigment in the broth. Prodigiosin was synthesized at a maximum level in the presence of inorganic phosphate concentrations suboptimal for growth. Concentrations of KH(2)PO(4) above 0.4 mM caused decreased pigment synthesis, whereas maximum cell growth occurred at 1.0 mM. Optimal growth and pigment production occurred in the presence of 8 to 16 mg of ferric ion . liter, with higher concentrations proving inhibitory to both growth and pigment production. Both growth and pigment production were found to decrease with increased concentrations of p-aminobenzoic acid. The highest specific concentration of prodigiosin (3,480 ng . mg protein) was observed in chemostat cultures at a dilution rate of 0.057 h. The specific rate of prodigiosin production at this dilution rate was approximately 80% greater than that observed in batch culture on defined medium. At dilution rates greater than 0.057 h, the concentration of cells decreased with increasing dilution rate, resulting in a profile comparable to that expected for linear growth kinetics. No explanation could be found for the linear growth profiles obtained for both batch and chemostat cultures.