Mechanisms underlying the manipulation of reproduction in female Tenebrio molitor by molecules produced by Hymenolepis diminuta
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.