Direct manipulation of insect reproduction by agents of parasite origin

Reproductive output of female Tenebrio molitor beetles is reduced upon infe ction with metacestodes of the rat tapeworm, Hymenolepis diminuta. We are u sing this as a model to investigate the adaptive significance of parasite-i nduced curtailment of insect reproduction. Production of the yolk protein v itellogenin (Vg) in the insect fat body is significantly reduced both in vi tro and in vivo by metacestodes. Synthesis can be measured by using [C-14]L -leucine incorporation, followed by immunoprecipitation. In this paper we d emonstrate that a significant decrease in [C-14]Vg can be produced by an ac etic acid extract of the parasite. Conclusive evidence is presented that th e active component(s) originate from the metacestodes: an extract of parasi tes grown entirely axenically has similar deleterious effects. The developm ental stage of the metacestode is important: immature (stage I-II) parasite s had greater capacity to suppress Vg synthesis than mature ones (stage TI- VI). Examination of the chemical nature of the effector molecule(s) reveale d that acetic-acid-extractable, boiling-resistant, pronase-sensitive agents in the molecular mass range 10-50 kDa reduced Vg synthesis by 47.4%. These data suggest that metacestodes produce a modulator molecule that directly affects insect vitellogenesis and, therefore, that reduction of host fitnes s may confer a selective advantage upon the parasite.