Sex differences in the profiles of prothoracic gland synthetic activity and of hemolymph ecdysteroid titers during development in the last larval instar of Rhodnius prolixus (Hemiptera).

The synthesis of ecdysteroids by prothoracic glands (PGs) of Rhodnius prolixus was measured in vitro by radioimmunoassay in both male and female larvae following initiation of development in the last larval instar by a blood meal. Neither ecdysteroid synthesis nor hemolymph titer differ between the sexes during the first few days following a blood meal. However, on Day 4 the PGs of female larvae commence a surge of increased synthesis, while in males this surge does not commence until Day 5. This 1 day difference is attributed to different times of activation of the PGs by prothoracicotropic hormone in male and female larvae. From Day 4 onward, differences between male and female larvae are described for both ecdysteroid synthesis and titer, both of which are more complex than a 1-day displacement of duplicate profiles. Both temporal and quantitative differences are detailed between males and females during Days 4-16 of development; ecdysteroid synthesis by PGs varies between males and females by up to fourfold on the same day. The hemolymph ecdysteroid titer profile closely follows that of PG synthesis for each sex. Both PG activity and titer in females decline 1 day ahead of males. The declining titer is known to influence the timing of ecdysis, and it was found that the median ecdysis time of females occurs 1 day before that of males even when males and females are synchronized with each other using a developmental marker on Day 14. We conclude that male and female PGs possess the intrinsic ability to synthesize ecdysteroids in a sex-specific pattern during development.(ABSTRACT TRUNCATED AT 250 WORDS)