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Title: Mechanisms of insects' resistance to viruses
Author: Saejeng, Aungkana
ISNI:       0000 0001 3544 7628
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2007
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This thesis investigated insect immunity against viral infection within the haemocoel. The first two chapters of the thesis are focused on the relatio~ship between the insect host, Plodia interpunctel/a and its granulosis DNA virus and two different routes of infection (oral inoculation and intrahaemocoelic injection). Techniques for the intrahaemocoelic injection of budded virus were developed. I showed that P. interpunctella response to virus by both routes of infection (oral inoculation and intrahaemocoelic injection) was dose-dependent. This suggests a systemic response to granulosis virus in P. interpunctel/a at both the gut and in the haemocoel. The sublethal effect of the virus on the pupal weight and developmental time were also examined. The results were compared with control larva groups (non-challenged larva, larvae injected with sterile water, and larvae injected with virus-free haemolymph). Sublethal effects on larvae pupal weight and prolonged developmental time of the virus were found only when the virus was orally inoculated. No sublethal effects ofthe virus were when the virus was injected into the haemocoel. The next two chapters applied the developed techniques of intrahaemocoelic injection to investigate the immune responses in the insect's haemocoel, I measured haemolymph phenoloxidase and in order to look for a evidence of a humoral immune response against viral infection. Haemolymph from controls and individuals subject to either oral inoculation or intrahaemocoelic injection were collected at set times post challenge. A new method was developed that quantified the collected haemolymph volume. The results demonstrated that the level of haemolymph PO activity in asymptomatic (resistant) larvae to both the oral inoculation and intrahaemocoelic injection did not differ from the control larvae. Haemolymph PO activity was only significantly higher in the inoculated groups when disease symptoms were observed, probably reflecting disease pathology. This suggests that haemolymph PO may not have a direct role against granulosis virus infection in this insect. The last chapter looks for evidence of antiviral activity in the haemolymph of virus-challenged larvae. The antiviral activity was tested in vivo by direct injection into the larvae which had previously been orally inoculated with three different doses of granulosis virus. Three different types of haemolymph were tested: (i) nonchallenged haemolymph, (ii) challenged haemolymph of orally infected subsequently . asymptomatic larvae, and (iii) challenged haemolymph of orally infected subsequently symptomatic larvae. The mortality rates and the dose-response of each larval treatment groups were compared with control larvae non-subjected -injection. The results suggest that there were antiviral components in the challenged larvae haemolymph whether they wer.e subsequently asymptomatic and symptomatic.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available