HYMENOLEPIS DIMINUTA-INDUCED FECUNDITY REDUCTION MAY BE CAUSED BY CHANGES IN HORMONE-BINDING TO TENEBRIO-MOLITOR OVARIES

Aspects of vitellogenesis, known to be controlled by juvenile hormone, are adversely affected by Hymenolepis diminuta infection of Tenebrio molitor, in spite of circulating titres of the hormone remaining uncha nged. It has therefore been proposed that juvenile hormone binding is disrupted at the tissue site level. Juvenile hormone III binding sites were located in the nuclear, microsomal and post-microsomal supernata nt fractions of the follicle cells of Tenebrio molitor. When JH-III bi nding was quantified for both control and Hymenolepis diminuta-infecte d beetles, binding in the nucleus and cytosol were found to be largely unaffected. However, microsomal binding was severely disrupted; on da ys 3 and 6 post-infection, binding was greatly diminished, on day 9 po st-infection, binding was slightly reduced and, by day 15, binding was 'restored' to that of control insects. Using follicle cell microsomes at day 3 post-infection, previous Scatchard analysis revealed the pre sence of at least two JH-III binding sites. The first is of higher aff inity, K-d = 5.3 x 10(-8) M, B-max = 1.5 x 10(-11) mol/mg protein and the second of lower affinity K-d = 7.7 x 10(-7) M, B-max = 9.75 x 10(- 11) mol/mg protein. A comparison with microsomal binding parameters of follicle cells from non-infected Tenebrio indicated that although the B-max values were unchanged, the K-d value of the higher affinity sit e was increased by approximately 5-fold. These data are indicative of a parasite-induced competitive binding inhibitor.