Degradation of juvenile hormone III in vitro by non-parasitized and parasitized Spodoptera exigua (Noctuidae) and by the endoparasitoid Chelonus inanitus (Braconidae)

Abstract

Parasitism of Spodoptera exigua by the solitary egg-larval parasitoid Chelonus inanitus induces precocious onset of metamorphosis, i.e. parasitized larvae construct a pupal cell and become prepupae in the fifth larval instar while non-parasitized larvae do so in the sixth larval instar. The parasitoid larva emerges as a freshly molted third instar larva from the precocious prepupa. A comparison of the metabolism of racemic 3H-JH III by homogenates of non-parasitized and parasitized larvae at the stage of pupal cell formation revealed that very similar amounts of juvenile hormone III diol, juvenile hormone III acid and juvenile hormone III acid-diol were formed. This shows that the changes in juvenile hormone degradation associated with metamorphosis, which occur in the sixth stadium in non-parasitized larvae, are precociously induced in parasitized larvae in the fifth stadium. In homogenates of parasitoid larvae, juvenile hormone III metabolizing activity was very low during the internal phase of development (first to second instar larvae) and almost excusively juvenile hormone III diol was formed. After emergence from the host, i.e. in third instar larvae, juvenile hormone III metabolic activity increased and esterases became active. In comparison to the host, specific juvenile hormone III degrading activities were always much lower in homogenates of parasitoid larvae than of host larvae. With homogenates of S. exigua eggs at a stage 2 3 of embryonic development and shortly before hatching, the pattern of juvenile hormone III metabolism was almost identical whether parasitized or not, and the major metabolite being formed was juvenile hormone III diol. This shows that parasitism by C. inanitus does not influence juvenile hormone metabolic activities at these stages.