Duncan A. Mackay

An experimental study of the relative humidity preference and survival of the Argentine ant, Linepithema humile (Hymenoptera, Formicidae): comparisons with a native Iridomyrmex species in South Australia

SummaryThe Argentine ant, Linepithema humile (Mayr), is a widespread invasive ant species that commonly displaces native ants and other ground-dwelling invertebrates in its introduced range. Previous studies have documented a relationship between the spread of Argentine ants and abiotic conditions (particularly water availability) in invaded areas, suggesting that the invasion success of Argentine ants may be related to specific abiotic factors. This study describes the relative humidity preferences and survival of Argentine ants and a dominant native ant, Iridomyrmex ‘rufoniger’ sp. group, in the laboratory. In a preference experiment, Argentine ant workers showed a significantly greater propensity than Iridomyrmex to locate themselves in containers with the highest relative humidity. A series of survival trials revealed that the survival of both species was related to the relative humidities within experimental containers. The survival of Argentine ant colonies was reduced in comparison with those of Iridomyrmex sp. after 4 h, however by 24 h both species displayed similar levels of survival in all relative humidity conditions. These findings confirm a relationship between the level of available moisture and the distribution and survival of Argentine ants, and may help to account for the current distribution and invasion success of Argentine ants in Australia.

Comparisons of Upper Thermal Tolerances Between the Invasive Argentine Ant (Hymenoptera: Formicidae) and Two Native Australian Ant Species

Abstract The Argentine ant, Linepithema humile (Mayr), is a significant pest species, having become established on almost every continent, particularly in areas with a Mediterranean climate. In its introduced range, the Argentine ant has been associated with reductions in the abundance and diversity of native ant and nonant invertebrate fauna, as well as the interruption of ant–plant mutualisms. The distribution of Argentine ants has been correlated with particular abiotic factors, including soil moisture, relative humidity, disturbance, and particular soil and vegetation types. This study assessed the importance of temperature on the survival of Argentine ants and two native ant species (Iridomyrmex “rufoniger” and Rhytidoponera “convexa”) in the laboratory. Workers were placed in incubators of varying temperatures (25, 32, 40, 45, 47, and 50°C), and counts of the numbers dead and alive were recorded after 1, 2, and 3 h. The results showed that all species displayed almost 100% survival at 25, 32, 40, and 45°C, but at 47°C the mortality rate of all species increased, with Argentine ants experiencing 100% mortality after 3 h. At 50°C, Argentine ants displayed no survival at 1 h, whereas the Iridomyrmex exhibited ≈50% survival after 3 h. These results may have significant implications in Australia, where the ground surface temperatures may become very high during the summer, potentially limiting the spread of Argentine ants.

Genetic structure, behaviour and invasion history of the Argentine ant supercolony in Australia

Biological invasions have significant ecological, evolutionary and economic consequences. Ants are exemplary invaders and their invasion success is frequently attributed to a shift in social structure between native and introduced populations. Here, we use a multidisciplinary approach to determine the social structure, origin and expansion of the invasive Argentine ant, Linepithema humile, in Australia by linking behavioural and genetic studies with indicators of dispersal pathways and propagule pressure. Behavioural assays revealed a complete absence of aggression within and between three cities – Melbourne, Adelaide and Perth – spanning 2700 km across Australia. Microsatellite analyses showed intracity genetic homogeneity and limited but significant intercity genetic differentiation. Exceptions were two Perth nests that likely represent independent translocations from Adelaide. These patterns suggest efficient local gene flow with more limited jump dispersal via transport corridors between cities. Microsatellite analyses of L. humile from potential source regions, combined with data from port interceptions, trade pathways and the timeline of spread within Australia, implicate the main European supercolony as the source of L. humile in Melbourne. Such an introduction probably then redistributed across Australia and spread to New Zealand to form an expansive Australasian supercolony.

Isolation of microsatellites from Baumea juncea (Cyperaceae)

We developed 13 polymorphic microsatellite loci for the rhizomatous perennial sedge Baumea juncea. The number of alleles per locus ranged from two to six, with averages of 3.0 and 3.2 at two South Australian populations. Observed and expected heterozygosity at variable loci within each population ranged from 0.034 to 1.000 and 0.034 to 0.766, respectively. These markers will allow the identification of genets, as well as the study of spatial genetic structure and genetic differentiation among populations.

Morphological variation and phylogenetic relationships within Eucalyptus series Subulatae (Myrtaceae) of southern Australia

Morphological variation within Eucalyptus series Subulatae, a group of mallee and woodland tree taxa distributed across southern Australia, was assessed by adult and seedling characteristics. A phenetic study included a total of 51 adult morphological characters and 37 seedling characters, which were assessed for 564 individuals representing 163 populations, covering the broad geographical distribution of the series. All taxa included in the series by either Johnson and Hill (1999) or Brooker (2000) were included together with E. angustissima, E. cooperiana, E. falcata and E. salmonophloia, all of which have been at times included in, or considered closely related to, E. ser. Subulatae. The phenetic analyses indicate that the four subseries of Brooker (2000) are morphologically distinct, although their distinctiveness is only evident from seedling characters. The two subseries that Johnson and Hill (1999) recognise (subser. Flocktonianosae and Transcontinentalosae) corresponding to Brooker’s (2000) subser. Decurrentes, are more weakly defined. Southern populations of E. dolichocera are not considered here to belong to this species but rather to belong to a different subseries based on seedling morphology. A phylogenetic analysis of 44 morphological characters and 23 species of E. ser. Subulatae and 24 species from variously related taxa suggest that E. ser. Subulatae may not be monophyletic. Eucalyptus brockwayi and E. salmonophloia are basal to E. ser. Subulatae and all of the other taxa included in the analysis. Within E. ser. Subulatae, subsers Oleaginae and Spirales are both monophyletic. Both the phylogenetic and phenetic analyses strongly suggest that E. brockwayi is unique in several characters, including some not previously recognised, and is best placed in a monotypic series. The position of E. aspersa remains unresolved, but is probably best retained in E. subser. Decussatae. A key to the subseries of E. ser. Subulatae is presented and putative intersubserial, interserial and intersectional hybrids involving the series are cited.

An experimental study of the impacts of cattle on spider communities of artesian springs in South Australia

The artesian springs that are located on the edge of the Great Artesian Basin in arid South Australia support diverse assemblages of spiders. Domestic or feral stock have affected the vegetation and substrate of artesian springs, which are important water sources. The effects of stock on the spider communities of artesian springs were investigated with a descriptive survey, comparing springs with differing grazing histories, and with a field experiment that simulated the impacts of cattle presence with trampling and mowing treatments. In the survey, the abundance of spiders was associated with the dominant vegetation cover and with the history of grazing pressure. In the experiment, the abundance of web-building and ambush-hunting spiders declined following mowing and/or trampling treatments. The use of foraging guilds is likely to be a useful approach in using spider communities as bioindicators of environmental change.

Geographic variation in extrafloral nectaries in the ant-associated plant genus Adriana (Euphorbiaceae) and its relationship to water availability

The relationship between geographic variation in extrafloral nectary size and climatic variation was assessed in three taxa within Adriana (Euphorbiaceae). In each taxon, there was a significant association between gland size and moisture-related climatic variables. A glasshouse experiment was conducted to examine the effect of water stress on nectary longevity, and it was found that the secretory activity of nectaries declined more rapidly on drought-stressed plants than on watered plants.

An experimental study of the pollination biology of the perennial halophyte Frankenia pauciflora var. gunnii (Frankeniaceae) in a South Australian salt marsh

Relatively little is known about the pollination biology or breeding systems of entomophilous plant species in salt-marsh habitats. In the present study, the pollination biology of the perennial halophyte Frankenia pauciflora DC. var. gunnii Summerh. (Frankeniaceae) was investigated in a salt marsh near Goolwa, South Australia. The flowering peak of this species occurs in summer and flowers are visited by a diverse array of insects in the Diptera, Hymenoptera and Lepidoptera. An experiment was performed to test for the presence of pollen limitation in the field. Flowers to which outcross pollen was added produced significantly more fruits and significantly more seeds per fruit than did unmanipulated control flowers. Average seed weight per fruit did not differ significantly between control and pollen-addition flowers. In glasshouse experiments, flowers to which cross-pollen was added produced significantly more fruit than did flowers to which self-pollen was added, suggesting the presence of a facultatively xenogamous breeding system.

Microsatellite markers for the freshwater shrimp Paratya australiensis (Atyidae)

Paratya australiensis is a common freshwater shrimp found in most catchments in south-eastern Australia. Microsatellite loci were isolated from a partial genomic library created using 454 sequencing. Of the 25 tested, 13 were found to be polymorphic, however, for pooling purposes only 12 were used for genotyping. The number of alleles per locus varied from 2 to 14 in a population from Wakefield River, South Australia, and the mean (range) observed and expected heterozygosity were 0.512 (0.136–0.909) and 0.590 (0.165–0.788), respectively across all alleles. These microsatellites will be used to study the genetic structure of populations in two catchments in South Australia.

Which species of Tortricidae leafrollers are key insect pests in South Australian vineyards

ABSTRACT Light brown apple moth, Epiphyas postvittana (Lepidoptera: Tortricidae) is regarded as the key insect pest in Australian vineyards and it is also an important pest of apples and citrus. E. postvittana is indigenous to Australia and has a wide geographical distribution. Recent observations suggest that leafroller species other than E. postvittana may be causing damage in grapevine canopies. A study of tortricids was undertaken in Adelaide Hills and McLaren Vale vineyards, South Australia. A total of 407 specimens of Tortricidae were collected from grapevine canopies. Molecular techniques were used to identify species. The mean prevalence of E. postvittana per sample was 91.0% in 2014/15 and 96.2% in 2015/16. Larval Acropolitis rudisana, lucerne leafroller, Merophyas divulsana and cotton tipworm, Crocidosema plebejana were also found on the grapevine canopy at much lower densities for the first time. The presence of leafroller species A. rudisana, M. divulsana and C. plebejana on grapevines confirms these species of Tortricidae may also be present in South Australian vineyards. This study confirms that E. postvittana is the most common tortricid pest in Adelaide Hills and McLaren Vale vineyards and also illustrates the utility of molecular methods in determining with confidence the species identity of larval Tortricidae.