Inhibition of vitellogenin synthesis in Apis mellifera workers by a juvenile hormone analogue, pyriproxyfen

Insect juvenile hormone (JH) has been related to modulation of vitellogenin (Vg) synthesis, a protein produced by fat body cells, secreted in haemolym ph and sequestered by developing oocytes. A stimulatory JH action has been described for the majority of species studied thus far. In some insects, ho wever, Vg synthesis has been inhibited or unaffected by JH. The aim of this study was to re-examine the action of JH on Vg synthesis in Apis mellifera workers, since contrasting effects of this hormone were described. Newly e merged worker bees were treated with different doses of pyriproxyfen (PPN), a potent JH analogue. Vg and total protein were quantified in haemolymph s amples of newly emerged up to 6-day-old worker bees. Protein synthesis acti vity of fat body cultured in vitro and ultrastructure of fat body cells wer e also examined. High doses (1.25, 2.5, 5 and 10 mu g) of PPN inhibited the onset and accumulation of Vg in the haemolymph of young worker bees in a d ose-dependent fashion. This inhibition was not a result of fat body cell de generation or death, as illustrated by fat body cells ultrastructure analys is, but by impairing Vg synthesis, as demonstrated by in vitro culture of f at body cells. Low doses (0.001, 0.01 and 0.1 mu g) neither affected the no rmal synthesis and secretion of Vg into the haemolymph nor caused an early onset of Vg in treated bees (which could be interpreted as a JH-activating effect), as shown by Vg quantification at 24-h intervals. The results sugge st that a low JH titre in honey bee workers permits the onset and accumulat ion of Vg in haemolymph, whereas high;IH levels turn off Vg synthesis. (C) 2000 Elsevier Science Ltd. All rights reserved.