Browsing by Author "Polson, A"

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    Three cocluded insect viruses : a biophysical and biological study of the nuclear-polyhedrosis virus of Colias electo, the granulosis virus of Heliothis armigera and the nuclear-polyhedrosis virus of Heliothis zea
    (1971) Gitay, Hela; Polson, A
    An investigation was undertaken in some detail of three virus strains of insect pests of agricultural importance, viz. a nuclear-polyhedrosis virus of the lucerne caterpillar, Colias electo, and a granulosis virus of the bollworm, Heliothis armigera, both found in South Africa, and a nuclear-polyhedrosis virus of the bollworm, Heliothis zea, isolated in America, with a view to ascertaining a knowledge of some of the fundamental properties and basic biology of these infective agents. On the basis of the information gained the viruses could be differentiated and their broad classification was established. The morphology of the polyhedra, capsules and virus particles observed by light and electron microscopy has been completed and measurements of the viral elements have been made. Some biophysical properties of the virus particles and their inclusion bodies were recorded, i.e. their resistance to chemical and physical treatments and their relative mobility in an electric field under standard conditions. Observations were made on procedures which brought about varying degrees of purification and concentration of the virus particles from putrefying larvae and the most successful of these were found to be reproducible. They involved the purification of the inclusion bodies and their digestion by weak alkali to release the virus particles. Both preparations of the viral elements were further purified by zone electrophoresis in sucrose density gradients. Some information was gathered on the mode of transmission of the infection from insect to insect by contact or cannibalism, from one generation to the next through the eggs, and particularly from one area to another by virus survival in avian faeces. The incidence and rate of the infection in the larvae was increased by environmental changes such as raising the temperature and also to some extent by spraying with a suspension of endospores of Bacillus thuringiensis. Exposure to other stress conditions was not successful in initiating a fatal infection in the insects. Of particular interest, however, was the observation that by injecting a 'foreign' virus a fatal infection was induced by activation of a native occult virus in the larvae of the silkworm, Bornbyx mori. In the context of the possible application of these infective agents to future methods of biological control of economically disastrous pests, these preliminary experiments were not unrewarding.
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    Viruses of Heliothis armigera (Hübner) (Lepidoptera : Noctuidae)
    (1977) Rubinstein, Riva; Polson, A
    Heliothis armigera (the bollworm) is a pest of agricultural importance in Southern Africa. It is often simultaneously infected with several insect viruses: nuclear polyhedrosis virus (NPV), granulosis virus (GV), and cytoplasmic polyhedrosis virus (CPV). Both NPV and GV have been previously studied because of their ready availability and their potential use in pest control. However, there have been no recorded studies of CPV in H. armigera because of the small amounts of virus present in the naturally infected larvae. Particular emphasis was therefore placed in this study on the CPV of H. armigera. CPV was successfully separated from naturally occurring NPV by a combination of techniques, such as differential centrifugation, density gradient zone electrophoresis and absorption with antibody to NPV. The CPV was then successfully propagated by passage in larvae reared on synthetic media. Pure CPV having been obtained, its replication and physico-chemical properties could be studied. Serological studies using immune electron microscopy and immune osmophoresis were used to detect and identify viruses of H. armigera and examine relationships between different CPVs. The gross morphological appearance of viral infections in H. armigera were studied. Distinctive features were observed both in larvae infected by NPV and in those infected by GV, but CPV-infected larvae were not markedly different in appearance from uninfected larvae. Larvae died readily from NPV or GV infection indicating their suitability for use in controlling H. armigera, but there was no larval mortality following CPV infection.