In most insects, female-specific egg-protein precursors (vitellogenins) are synthesized during pupal or adult stages in response to 20-hydroxyecdysone and/or juvenile hormone. In the gypsy moth, two female-specific haemolymph polypeptides (apo-vitellogenins) having electrophoretic and immunologic identity with Lymantria dispar egg-vitellin apo-proteins begin to accumulate in the haemolymph after day 3 of the fifth larval instar. Head ligation, starvation or treatment with doses of a juvenile hormone analogue, methoprene, >10 μg prior to day 3 block the accumulation of apo-vitellogenin in the haemolymph. Unlike head-ligated or starved larvae which do not gain weight and do no accumulate normal levels of non-vitellogenin haemolymph proteins following treatment, methoprene-treated larvae grow normally and accumulate non-vitellogenin haemolymph proteins. 20-Hydroxyecdysone (2.5 μg) has no effect on the haemolymph accumulation of apo-vitellogenins in normal larvae, and does not restore haemolymph apo-vitellogenins in methoprene-treated, head-ligated or starved larvae. The above results suggest that a low (or declining) juvenile hormone titre during a critical stage early in the last larval instar (prior to day 3) is necessary for the accumulation of vitellogenin in the haemolymph to proceed normally in the gypsy moth. Other factors such as nutrient intake may also be involved. This role of juvenile hormone as an inhibitor of vitellogenin accumulation/synthesis is a novel one for insect species.
All Science Journal Classification (ASJC) codes
- Insect Science