Stimulation of JH biosynthesis by the corpora allata of adult female Aedes aegypti in vitro: effect of farnesoic acid and Aedes allatotropin

Abstract

Previous studies have demonstrated that the synthesis of juvenile hormone (JH) by the isolated corpora allata (CA) complex in vitro as well as the JH titer in the yellow fever mosquito Aedes aegypti are elevated before feeding and low after a blood meal. In the present study, we used an in vitro radiochemical assay to analyze the effect of farnesoic acid (FA) and Aedes allatotropin (Aedes-AT) on the biosynthesis of JH and methyl farnesoate (MF) by the isolated CA complex of A. aegypti adult female. CA complex from day-0 females (0-1 h after emergence) exhibited a low basal juvenile hormone III (JH III) biosynthetic activity and did not respond to either allatotropic or FA stimulation. However, incubation of CA complexes from newly emerged females with Aedes-AT plus FA resulted in very high production of JH III. This is the first report suggesting that allatotropin makes corpora allata in newly emerged females capable for JH biosynthesis. When we studied CA complexes dissected from females 1 day after emergence, the stimulatory action of Aedes-AT was strong and dose-dependent, with maximum stimulation in the range of 10(-8)-10(-9) mol l(-1), suggesting that Aedes-AT is indeed a true allatotropin (a molecule with allatotropic activity) in A. aegypti. The addition to the culture medium of 40 micro mol l(-1) FA, a JH precursor, resulted in a 9-fold increase in JH III biosynthesis in 2-, 4- and 6-day-old sugar-fed females. The two major labeled products synthesized by the stimulated CA complex were identified as JH III and MF by RP-HPLC and GC-MS. Treatment of CA complexes with FA, but not Aedes-AT, resulted in an increase in MF. Application of both Aedes-AT and FA to the CA complexes of 2-, 4- and 6-day-old females resulted in the same effects as FA alone. These data suggest that in sugar-fed females, FA and Aedes-AT exert different effects on the terminal steps in JH biosynthesis.