| Summary: | Metacestodes of Hymenolepis dirninuta cause a reduction in the reproductive success of Tenebrio rno/itor by interfering with the process of vitellogenesis. The parasite produces a molecule that causes a decrease in the synthesis of vitellogenin (Vg) in the beetle host. This thesis provides an account of the progress towards the isolation of this molecule and attempts to determine its mode of action. The parasite molecule is a small peptide, as determined by its chemical nature. It is pronase sensitive and heat insensitive, has a strong absorbance at 215nm and is blocked at both the NH2- and COOH-terminals. Two putative modes of action of the parasite manipulator molecule have been explored, namely induction of apoptosis of fat body cells or alteration of Vg mRNA abundance. The levels of chromatin condensation and DNA fragmentation in fat body nuclei are significantly elevated upon infection in vivo, indicating increased apoptosis. However, fat body tissue from non-infected females cultured with live parasites did not exhibit an increase in the levels of apoptosis. This suggests that apoptosis is not induced by the parasite molecule. Follicle resorption in the ovaries was also examined. Although there is a significant increase in the number of ovarioles undergoing resorption in H dirninutainfected T. molitor, the cause is not follicle cell apoptosis.
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