Metamorphosis, activity of juvenile-hormone esterase and alteration of ecdysteroid titres: Effects of larval density and various stress on the red flour beetle, Tribolium freemani Hinton (Coleoptera: Tenebrionidae)

When a larva of the red flour beetle Tribolium freemani (Hinton) was introduced into a vial, the larva pupated within 6 days, whereas when two larvae were introduced, the larvae pupated in 12 days. Crowded larvae delayed production of juvenile-hormone esterase (JHE) and release of ecdysteroids, as measured by radioimmunoassay, compared with the isolated larvae. The highest JHE activity was observed at pupal ecdysis in both groups and there were increases in whole-body ecdysteroid levels during the last part of intermoult before pupation and adult emergence, which coincided with decreases in ecdysteroid titres in both isolated and crowded groups. Cold shock, heat stress, the JHE inhibitor methamidophos, and juvenile hormone (JH) I delayed pupation in isolated larvae. Cold shock, heat stress and methamidophos reduced the JHE activity, and cold shock and JH I reduced ecdysteroid levels in isolated larvae. Light, vibration and a nonsteroidal ecdysteroid agonist RH 5849 stimulated pupation in crowded T. freemani larvae, which was antagonized by JH I. The JHE activity and ecdysteroid levels were higher in crowded larvae reared under 24 h light or treated with vibration, octopamine agonists and precocene II than those control larvae kept in constant darkness.