Some aspects of the animal ecology of Rhenosterbos: Elytropappus rhinocerotis (L.f.) Less
- Authors: Shiff, Clive Julian
- Date: 1957
- Subjects: Animal ecology -- South Africa , Rhenosterbos
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5880 , http://hdl.handle.net/10962/d1013200
- Description: Rhenosterbos, Elytropappus rhinocerotis (L.f.) Less belongs to a purely South African section ot the Compositae. It is restricted to an area of low rainfall which is evenly distributed over the year. The plant is a specialised xerophyte with minute leaves and white pubescent twiglets. Older stems become woody and dry and bear no leaves. The shrubs have a life span of about eight years; the plants are most succulent and luxurious during the third and fourth year, after which they tend to become woody and scraggly. For this investigation insect material was obtained by sweep-net collection and field observation. In the Grahamatown district 78 collections were made during the period March - November 1953, with data thus obtained being embodied in this work. In addition to this, collections were made in the Cradock-Hofmeyer, Uitenhage, Riversdale, Bot River, Swellendam and Stellenbosch districts. Twenty species of insects have been shown definitely to feed on the plant and there are another 13 which probably feed on it. Of the 20 species attached to the plant, 12 are sucking forms belonging to the Orders Homoptera and Hemipters. They include six Coccids, two Jassids a Cercopid, two Mirids and a Pentstomid. The Coleoptera are represented by one or perhaps two species which feed on the plant. The Lepidoptera are represented by two important species of moth, a Geometrid and a Pyralid. Four species of gall forming Diptera are associated with the plant. There are two species of Trypetidae which are responsible for piriform swellings of growth points and are distributed evenly throughout the bush. There are also two Cecidomyidae one of which develops in the growth points of the shoots and is responsible tor a minute tubular gall. The other develops in a fusiform stem gall. This latter gall has been shown to be more common on smaller bushes than on larger ones, implying that the adult female may show certain selective powers during oviposition. The size of the insect population is held in check by spiders mantids and other general predators. There are several Coccinellids which prey on the scale insects. Rhenosterbos supports a small, well regulated community of insects. The balance between plant and animal is very dellcate because of the high degree of specialisation of the plant. On occasions this balance has been known to break down, and the insects present in abundance have swamped and killed large patches of the plant.
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- Authors: Shiff, Clive Julian
- Date: 1957
- Subjects: Animal ecology -- South Africa , Rhenosterbos
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5880 , http://hdl.handle.net/10962/d1013200
- Description: Rhenosterbos, Elytropappus rhinocerotis (L.f.) Less belongs to a purely South African section ot the Compositae. It is restricted to an area of low rainfall which is evenly distributed over the year. The plant is a specialised xerophyte with minute leaves and white pubescent twiglets. Older stems become woody and dry and bear no leaves. The shrubs have a life span of about eight years; the plants are most succulent and luxurious during the third and fourth year, after which they tend to become woody and scraggly. For this investigation insect material was obtained by sweep-net collection and field observation. In the Grahamatown district 78 collections were made during the period March - November 1953, with data thus obtained being embodied in this work. In addition to this, collections were made in the Cradock-Hofmeyer, Uitenhage, Riversdale, Bot River, Swellendam and Stellenbosch districts. Twenty species of insects have been shown definitely to feed on the plant and there are another 13 which probably feed on it. Of the 20 species attached to the plant, 12 are sucking forms belonging to the Orders Homoptera and Hemipters. They include six Coccids, two Jassids a Cercopid, two Mirids and a Pentstomid. The Coleoptera are represented by one or perhaps two species which feed on the plant. The Lepidoptera are represented by two important species of moth, a Geometrid and a Pyralid. Four species of gall forming Diptera are associated with the plant. There are two species of Trypetidae which are responsible for piriform swellings of growth points and are distributed evenly throughout the bush. There are also two Cecidomyidae one of which develops in the growth points of the shoots and is responsible tor a minute tubular gall. The other develops in a fusiform stem gall. This latter gall has been shown to be more common on smaller bushes than on larger ones, implying that the adult female may show certain selective powers during oviposition. The size of the insect population is held in check by spiders mantids and other general predators. There are several Coccinellids which prey on the scale insects. Rhenosterbos supports a small, well regulated community of insects. The balance between plant and animal is very dellcate because of the high degree of specialisation of the plant. On occasions this balance has been known to break down, and the insects present in abundance have swamped and killed large patches of the plant.
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Some aspects of the insect ecology of citrus orchards
- Authors: Smithers, Courtenay Neville
- Date: 1954
- Subjects: Citrus -- Diseases and pests , Insect pests
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5883 , http://hdl.handle.net/10962/d1013231
- Description: After a brief introduction, the species of Citrus on which the investigations were carried out are mentioned. This is followed by an account of the methods of collection used, and a discussion of their relative merits. The main method used was that in which the trees were fumigated with hydrocyanic acid gas, and the insects falling from the trees were taken up on sheets. The location of the areas where collections were made are then given. An annotated list of the species taken by the fumigation method follows, and the numerical data obtained at the same time regarding the species present is given in an abbreviated form and discussed. A more detailed discussion of the relative abundance of the species is then undertaken. The discussion of the ecology of the insects commences with the insects listed according to their activities, so far as known, and an account of five trees of striking faunal differences is given. A broader discussion of citrus ecology is then given, based on the data previously presented; this ends with a short reminder of the inherent 'oneness' of the insect with its environment.
- Full Text:
- Authors: Smithers, Courtenay Neville
- Date: 1954
- Subjects: Citrus -- Diseases and pests , Insect pests
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5883 , http://hdl.handle.net/10962/d1013231
- Description: After a brief introduction, the species of Citrus on which the investigations were carried out are mentioned. This is followed by an account of the methods of collection used, and a discussion of their relative merits. The main method used was that in which the trees were fumigated with hydrocyanic acid gas, and the insects falling from the trees were taken up on sheets. The location of the areas where collections were made are then given. An annotated list of the species taken by the fumigation method follows, and the numerical data obtained at the same time regarding the species present is given in an abbreviated form and discussed. A more detailed discussion of the relative abundance of the species is then undertaken. The discussion of the ecology of the insects commences with the insects listed according to their activities, so far as known, and an account of five trees of striking faunal differences is given. A broader discussion of citrus ecology is then given, based on the data previously presented; this ends with a short reminder of the inherent 'oneness' of the insect with its environment.
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Some comparative studies of the fauna in soils developed under natural forest, pine and bluegum
- Watts, John Christopher David
- Authors: Watts, John Christopher David
- Date: 1952
- Subjects: Soil science , Forest ecology , Soil animals
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5895 , http://hdl.handle.net/10962/d1013423
- Description: [From Introduction] It has been said that, "If a nation saves its trees, the trees will save the nation." The truth of this assertion is apparent in many parts of the world today. In South Africa, fires and demands in the past for timber have led to extensive depletion of the Natural Forests. In many cases, natural revegetation has been slow to develop and deterioration of the soil has resulted. The desire to replace the tree cover and at the same time to meet an increasing internal demand for timber, has led to widespread planting of Pine and Bluegum. It is probable that more trees have now been planted than were destroyed in the past. The silviculturist however, who develops a pure stand on land which previously supported the mixed stand, should anticipate a change in soil properties as a natural accompaniment of such an undertaking. The nature of this change is the primum mobile of the present comparative study. The forest soils studied were taken in the Cape Province in the following areas:- Grahamstown; Amatola Mountains, District Alice; Witte-els-Bosch, District Humansdorp, during the course of a year. The physical and chemical properties, and the faunal composition of the soil samples were examined in relation to the different tree covers. Because of the necessity of taking large numbers of samples and thorough examination of these to arrive at a definite conclusion, the work is necessarily incomplete. It is felt however that the results obtained justify a further study of this aspect of soil biology.
- Full Text:
- Authors: Watts, John Christopher David
- Date: 1952
- Subjects: Soil science , Forest ecology , Soil animals
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5895 , http://hdl.handle.net/10962/d1013423
- Description: [From Introduction] It has been said that, "If a nation saves its trees, the trees will save the nation." The truth of this assertion is apparent in many parts of the world today. In South Africa, fires and demands in the past for timber have led to extensive depletion of the Natural Forests. In many cases, natural revegetation has been slow to develop and deterioration of the soil has resulted. The desire to replace the tree cover and at the same time to meet an increasing internal demand for timber, has led to widespread planting of Pine and Bluegum. It is probable that more trees have now been planted than were destroyed in the past. The silviculturist however, who develops a pure stand on land which previously supported the mixed stand, should anticipate a change in soil properties as a natural accompaniment of such an undertaking. The nature of this change is the primum mobile of the present comparative study. The forest soils studied were taken in the Cape Province in the following areas:- Grahamstown; Amatola Mountains, District Alice; Witte-els-Bosch, District Humansdorp, during the course of a year. The physical and chemical properties, and the faunal composition of the soil samples were examined in relation to the different tree covers. Because of the necessity of taking large numbers of samples and thorough examination of these to arrive at a definite conclusion, the work is necessarily incomplete. It is felt however that the results obtained justify a further study of this aspect of soil biology.
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