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  • 1
    Electronic Resource
    Electronic Resource
    The appetence behaviour of two South African paralysis-inducing ixodid ticks (1993)
    Springer
    Experimental and applied acarology 17 (1993), S. 921-930 
    Details
    ISSN: 1572-9702
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The appetence responses of the ixodid ticksIxodes rubicundus andRhipicephalus punctatus to various stimuli were quantified under laboratory conditions. A greater percentage ofI. rubicundus generally responded to the different stimuli at lower than at higher temperatures while the converse was usually true forR. punctatus. Radiation heat and shadowing evoked a response in the greatest percentage ofI. rubicundus, whereas CO2 and host odour were responsible for a similar reaction inR. punctatus. A single perturbation of the substrate caused more than 50% ofI. rubicundus to respond while constant perturbation resulted in a progressive decrease in the proportion of ticks reacting. Significantly moreR. punctatus thanI. rubicundus were attracted to a CO2 trap and theR. punctatus were also attracted to the trap over a greater distance. Significantly more older than younger ticks of both species responded to the various stimuli.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02328069
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Observations on the relation between phytoplankton diversity and environmental factors in the Vaal River at Balkfontein, South Africa (1988)
    Springer
    Hydrobiologia 169 (1988), S. 199-207 
    Details
    ISSN: 1573-5117
    Keywords: Riverine environment ; phytoplankton community structure ; Shannon-Wie H′ and Hurlbert PIE indices
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The relationship between specific environmental factors as independent variables and temporal changes in phytoplankton community structure in the Vaal River (a turbid system) during 1984 was investigated by employing different diversity indices. Temporal changes in community structure reflected temporal changes in certain environmental factors. Phytoplankton diversity, measured with Shannon-Wie H' and Hurlbert PIE indices, was related firstly to discharge and discharge derived variables (such as SO4, Si, N and P loading) and secondly to turbidity derived variables (such as euphotic zone depth). Discharge appears to be of prime importance in affecting diversity. Observations were made that shed new light on conditions contributing to the development of an August peak (dominated by Stephanodiscus hantzschii fo. tenuis and Micractinium pusillum) in phytoplankton concentration. Increased environmental stress may reduce the number of sensitive species, thus reducing interspecific competition between tolerant species which could then exploit the — for them — more favourable conditions resulting in an increase in their numbers to peak concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00007311
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  • 3
    Electronic Resource
    Electronic Resource
    An evaluation of strategic and threshold control measures against the Karoo paralysis tick, Ixodes rubicundus (Acari: Ixodidae) in South Africa (1995)
    Springer
    Experimental and applied acarology 19 (1995), S. 147-153 
    Details
    ISSN: 1572-9702
    Keywords: Tick control ; strategic ; threshold ; Karoo paralysis ; Ixodes rubicundus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Paralysis caused by feeding female Ixodes rubicundus ticks is a major problem in large areas of South Africa. As the life cycle of the tick extends over a period of 2 years, it was hypothesized that strategic treatment of sheep with an acaricide over a 2 year period, timed to kill most engorging females, should markedly lower the biotic potential of the tick. Two flocks of sheep grazing in separate paddocks known to be infested with I. rubicundus were treated either strategically or on a threshold basis (i.e. only when tick challenge exceeded a predetermined critical level in terms of paralysis) for a 2 year period. The tick burdens of untreated control sheep running with the two flocks were monitored over a 4 year period and their seasonal dynamics determined. The times at which peak infestations occurred were similar for both flocks of sheep, but significant differences in mean tick burdens between the two flocks were recorded. Tick numbers on sheep in the strategically treated flock did not decrease during the third and fourth years of the trial as was expected. Possible reasons for this were low stocking densities, especially during times of peak abundance of adults and the presence of wild hosts which maintained tick populations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00046285
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  • 4
    Electronic Resource
    Electronic Resource
    Sites of attachment and intraspecific infestation densities of the brown paralysis tick (Rhipicephalus punctatus) on Angora goats (1991)
    Springer
    Experimental and applied acarology 12 (1991), S. 243-249 
    Details
    ISSN: 1572-9702
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Significant differences in the distribution of brown paralysis ticks on various age classes of Angora goats were recorded. In kids, most (〉98%) of the ticks attached to the head and ears, whereas in older groups, in addition to the ears, a high proportion (〉20%) of ticks also attached to the ventral side of the neck. There were significant differences in the mean infestation densities of both male and femaleR. punctatus in kids and older animals. These differences were, however, only significant for the first two sample dates involving kids, and are probably related to behavioural attributes of the kids which enhance tick/host contact. Newly born Angora goat kids are considered a high-risk group with regard to paralysis caused by the brown paralysis tick. Methods of avoiding mortality amongst kids are suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01193470
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  • 5
    Electronic Resource
    Electronic Resource
    Spatial distribution of the Karoo paralysis tickIxodes rubicundus (Acari: Ixodidae) within a false upper Karoo veld type (1991)
    Springer
    Experimental and applied acarology 11 (1991), S. 37-49 
    Details
    ISSN: 1572-9702
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Spatial distribution of the Karoo paralysis tick (Ixodes rubicundus) has been studied in a paralysis enzootic area of the southwestern Orange Free state. Significantly more females than males were collected from the vegetation. Most ticks (99%) used grass as questing sites at a height of approximately 45 cm (range 10–97 cm), which correlates with the size of host animals. No significant differences between the questing height of male and fermale ticks were evident. The ticks were found on most of the grass species present and, except for the genusEragrostis no specific preference was evident. When questing, the capitulum ofI. rubicundus is usually (90%) directed towards the ground. Seventy-eight percent of the ticks occurred singly on a specific grassblade or flowerhead. In those cases where two ticks occurred together, no sexual aggregation was evident. Most ticks occurred under or close ( $$\bar x$$ =62 cm) to the corwn cover of specific shrub or tree species. These plant species were characterized by a dense crown cover with a mat of decaying leaf litter underneath. The preference of the tick for wild olive trees (Olea europaea fricana) suggests that except for the physical characteristics of this tree species, host factors may also be important. Significantly more ticks were distributed on the cooler, more protected southern sides of vegetation in comparison to the northern sides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01193727
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  • 6
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    Observations on the relation between phytoplankton diversity and environmental factors in the Vaal River at Balkfontein, South Africa (1988)
    Springer
    Details
    Publication Date: 1988-11-01
    Print ISSN: 0018-8158
    Electronic ISSN: 1573-5117
    Topics: Biology
    Published by Springer
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  • 7
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    Modeling the minimum enzymatic requirements for optimal cellulose conversion (2013)
    Institute of Physics
    Details
    Publication Date: 2013-04-26
    Print ISSN: 1748-9318
    Electronic ISSN: 1748-9326
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by Institute of Physics
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