Vitellogenin uptake, not synthesis, is dependent on juvenile hormone in adults of Phormia regina (Meigen)

When Phormia regina larvae were raised on an artificial diet, topical applications of either methoprene (2.5 μg/fly) or juvenile hormone III (5 μg/fly) to adult, sugar-fed, females on days 3, 4 and 5 after emergence caused from 10.2 to 17.5% to have stage 4 follicles (i.e. as judged by the presence of a little opaque material in the oöcytes); whereas, in both the untreated and the acetone controls, oöcytes remained in stage 3, in nearly all flies, without any opaque material. Previous studies by other researchers on methoprene-treated, sugar-fed P. regina referred to the opaque material in stage 4 follicles as yolk. In this present study, however, examination, using a specific enzyme-linked immunosorbent assay (ELISA) for vitellin and vitellogenin, of stage 4 follicles as well as the haemolymph from sugar-fed and methoprene (or juvenile hormone III)-treated flies, revealed no vitellin or vitellogenin, respectively. These results are consistent with our previous data, which have shown that juvenile hormone is mainly involved with vitellogenin uptake but not vitellogenin biosynthesis. Thus our present results are inconsistent with a previous conclusion indicating that methoprene treatment would cause vitellogenin biosynthesis and complete egg development in sugar-fed P. regina raised as larvae on pork liver. When we raised larvae on pork liver, we found that topical application of methoprene (three times) to 195 sugar-fed females resulted in only one female containing stage 10 ovaries and 112 contained stage 3, 74 stage 4, and eight stages 5–9 ovaries. None of the methoprene induced stage 4 follicles showed any detectable quantity of vitellin. Since methoprene treatment resulted in only one fly (out of 195) to have stage 10 follicles (albeit the vitellin deficiency), our results do not support the idea that juvenile hormone treatment alone is sufficient to initiate and sustain vitellogenin biosynthesis and uptake in sugar-fed P. regina.