The population dynamics of the mediterranean snails Cernuella virgata, Cochlicella acuta (Hygromiidae) and Theba pisana (Helicidae) in pasture - cereal rotations in South Australia: a 20-year study

2008 ◽  
Vol 48 (12) ◽  
pp. 1514 ◽  
Author(s):  
G. H. Baker

The snails Cernuella virgata, Cochlicella acuta and Theba pisana are introduced pests of grain crops and pastures in southern Australia. The population dynamics of these three species of snail were studied for 20 years in two adjacent fields where they coexisted on a farm on the Yorke Peninsula in South Australia. The fields were used for pasture–cereal rotations. Surveys were conducted in autumn and spring each year, coinciding respectively with the start of the breeding season and peak abundance of snails (mostly juveniles). Populations varied greatly in abundance between years and between species, but snails were generally most common in spring, in wet years, especially those with wet autumns and wet springs. Rainfall early in a particular year (i.e. at sowing of crops in autumn) can thus be used to predict the likelihood of heavy snail infestations later in spring (i.e. at harvest). In contrast, the abundance of adult snails in autumn was a poor predictor of the subsequent abundance of juvenile snails in spring, especially in crops. There were no significant correlations, at field scale, between the average abundance of the three species of snail in spring, in either pastures or crops. However, at a sampling scale of 0.25 m2, there were consistent, negative relationships between the abundance of all three snail species. Such patterns may reflect either competitive interactions between snails or subtle differences in micro-habitat choice. Patterns in the abundance of snails (e.g. large numbers near field edges) were suggestive of occasional invasion from dense populations in adjacent fields.

Author(s):  
Geoff H Baker

ABSTRACT Two Mediterranean snails, Theba pisana and Cernuella virgata, are agricultural pests in southern Australia. The two species are rarely found together in large numbers in the field, at small scales (<1 m2). In laboratory experiments, the presence of T. pisana reduced the survival of C. virgata, but only when food (carrot + lettuce) was provided. When C. virgata was exposed to only the mucus trails and faeces of T. pisana, produced while feeding on lettuce, both the survival and activity of C. virgata were reduced. When carrot was substituted for lettuce, there was less effect. In addition, when C. virgata was exposed to T. pisana’s faeces only, derived from access to a mix of lettuce and carrot, there was no effect on C. virgata’s survival. The observed reductions in the survival of C. virgata were stronger in autumn (the breeding season for both snail species) compared with spring. Inhibitory components within the mucus trails of T. pisana may (1) help explain the observed distribution patterns of the two species at small scales in the field and (2) provide a novel method for control of pest populations of C. virgata, in some situations.


2005 ◽  
Vol 53 (6) ◽  
pp. 375 ◽  
Author(s):  
A. R. Butcher ◽  
D. I. Grove

Brachylaima cribbi is a terrestrial trematode parasite of humans and other mammals, birds and reptiles, with helicid and hygromiid summer-aestivating land snails acting as first and second intermediate hosts. Beginning in April, seasonal variations in rates of sporocyst and metacercarial infection by B. cribbi were studied in Cochlicella acuta, Cernuella virgata and Theba pisana over 1 year at four ecologically diverse sites on the Yorke Peninsula, South Australia. The overall mean sporocyst prevalence rate in April was 2.7%. Sporocyst prevalences peaked during spring (10–78% for C. acuta, 12–44% for C. virgata and 10–18% for T. pisana). Metacercarial infection rates varied markedly from 10% to 98% at the start of the study. Overall metacercarial infection rates peaked with winter rains for T. pisana (average 50% infected) and in spring for C. acuta and C. virgata (average 80% infected) then declined in summer for all species. The average numbers of metacercariae per infected snail over the study period were 5.4 for C. virgata, 3.9 for C. acuta and 2.2 for T. pisana, with maximum numbers in winter or spring. Conditions on the Yorke Peninsula favour hyperinfection with this parasite.


Insects ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 865
Author(s):  
Kate A. Muirhead ◽  
Kym D. Perry

Two conical snail species introduced to Australia from the Mediterranean region during the 20th century are major pests of pastures and grain crops. In 2000, a parasitoid fly, Sarcophaga villeneuveana, was introduced into South Australia for biocontrol of the conical snail, Cochlicella acuta. The fly successfully established in the region but assessments of its impact in different snail aestivation microhabitats were limited. Twenty years on, field surveys were conducted to assess the geographic distribution and parasitism rates of S. villeneuveana on conical snails in the Yorke Peninsula region. Nineteen sites were sampled on four occasions in January and April of both 2019 and 2020. In total, >85,600 C. acuta and >2400 C. barbara were collected from cryptic (ground or plant refuge) and exposed (open ground or elevated substrate) aestivation habitats and assessed for parasitism. The fly was detected at 13 of 19 sampled sites up to 34 km from nursery release sites. Total parasitism rates of suitably sized snails (≥5 mm shell height) were 2.9% for C. acuta and 3.4% for C. barbara. Maximum parasitism rates of 48% for C. acuta and 29% for C. barbara were found at sites adjacent to spring- and summer-flowering native vegetation. Across 13 sites, parasitism rates were higher for C. acuta (5.4%) and C. barbara (15.2%) in exposed habitats above ground level. However, only 34% of C. acuta and 14% of C. barbara were found in elevated habitats as most snails were found in cryptic refuges. There was a seasonal decline in abundance of C. acuta (66%) and C. barbara (45%) between January and April, suggesting natural mortality. Although the overall impact of the fly is limited, high parasitism rates in local environments with flowering resources indicates the potential to enhance biocontrol of both invasive conical snail species.


2007 ◽  
Vol 101 (5) ◽  
pp. 1323-1330 ◽  
Author(s):  
Helen P. Waudby ◽  
Sophie Petit ◽  
Bruce Dixon ◽  
Ross H. Andrews

2018 ◽  
Vol 194 ◽  
pp. 239-256 ◽  
Author(s):  
Keryn Wolff ◽  
Caroline Tiddy ◽  
Dave Giles ◽  
Steve M. Hill

1996 ◽  
pp. 401-414 ◽  
Author(s):  
WESLEY R. STRONG ◽  
DONALD R. NELSON ◽  
BARRY D. BRUCE ◽  
RICHARD D. MURPHY

1996 ◽  
Vol 160 ◽  
pp. 363-364
Author(s):  
S.A. Dazeley ◽  
P.G. Edwards ◽  
J.R. Patterson ◽  
G.P. Rowell ◽  
M. Sinnott ◽  
...  

TheCollaboration ofAustralia andNippon for aGAmmaRayObservatory in theOutback operates two large telescopes at Woomera (South Australia), which detect the Čerenkov light images produced in the atmosphere by electronpositron cascades initiated by very high energy (~1 TeV or 1012eV) gamma rays. These gamma rays arise from a different mechanism than at EGRET energies: inverse Compton (IC) emission from relativistic electrons.The spoke-like images are recorded by a multi-pixel camera which facilitates the rejection of the large numbers of oblique and ragged cosmic ray images. A field of view ~3.5° is required. The Australian team operates a triple 4 m diameter mirror telescope, BIGRAT, with a 37 photomultiplier tube camera and energy threshold 600 GeV. The Japanese operate a single, highly accurate 3.8 m diameter f/1 telescope and high resolution 256 photomultipler tube camera. In 1998 a new 7 m telescope is planned for Woomera with a design threshold ~;200GeV.


1988 ◽  
Vol 78 (3) ◽  
pp. 493-509 ◽  
Author(s):  
Garrick McDonald ◽  
Roger A. Farrow

AbstractAerial sampling for Nysius vinitor Bergroth was undertaken in the surface and upper air, at altitudes of 2 and 100-300 m, respectively, at Trangie in central New South Wales and at Corny Point, Yorke Peninsula, South Australia. Insects were sampled for 15 periods, each of 3-11 days, between October 1979 and February 1984, covering all months except January, March and May. N. vinitor was one of the most abundant insects caught in the upper air during the day and night (mean density of 652/106 m3), while the congeneric N. clevelandensis Evans was rarely caught at any time. N. vinitor was caught in all months sampled except for the winter months of July and August, and the largest daily catches occurred in September. Females were generally less common than males, although the relative incidence in the upper air catches frequently increased significantly from day to night. Fewer mature females were caught in the upper air (0-16·8%) than at the surface (0-48·4%). Densities were generally much greater in the surface air than in the upper air, although during the major flights of spring, there was less than a two-fold difference, indicating increased migratory activity. Migration occurred in a range of synoptic conditions resulting in the displacement of individuals in a variety of directions and distances depending on synoptic flow at the time of flight. Major migrations occurred at night, following dusk take-off, in disturbed weather associated with prefrontal airflows. These resulted in net southward displacements of ca 200-300 km depending on flight duration. It is suggested that major immigration flights into central-western New South Wales and regions to the south regularly occur in early spring (September-October) and probably arise from breeding areas in subtropical latitudes.


Author(s):  
William Mude ◽  
Lillian Mwanri

This paper was part of a large study that aimed to explore determinants of increased suicides among African youths in South Australia. As part of this larger study, narratives from participants indicated that identity crisis could be a potential determinant of suicide. This paper reports on how African youths negotiate and form identity in Australia. A qualitative inquiry was undertaken with 31 African youths using a focus group and individual interviews. Data analysis was guided by a framework for qualitative research. These youths negotiated multiple identities, including those of race, gender, ethnicity and their origin. ‘Freedom and opportunity’, ‘family relationships’, ‘neither belonging here nor there’ and ‘the ability to cope against the paradox of resourcefulness in Australia’ appeared to be important themes in negotiating individual identities. An opportunity was used to acknowledge privileges available in Australia relative to Africa. However, the extent to which individuals acted on these opportunities varied, affecting a person’s sense of purpose, identity formation and belonging in Australia. The loss of social networks following migration, and cultural differences between African and Australian societies, shaped the experience of belonging and identity formation. These findings are crucial as they indicate the need for policies and practices that consider experiences of youths as they form their identity in Australia. Further studies with large numbers of participants are needed to explore these issues further among African youths in Australia.


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