METAMORPHOSIS OF THE RED FLOUR BEETLE, TRIBOLIUM-FREEMANI HINTON (COLEOPTERA, TENEBRIONIDAE) - ALTERATION OF OCTOPAMINE CONTENT MODULATES ACTIVITY OF JUVENILE-HORMONE ESTERASE, ECDYSTEROID LEVEL, AND PUPATION

Under crowded conditions, Tribolium freemani larvae exhibited a delay in the increase of octopamine (OA) content, activity of juvenile-hormo ne esterase (JHE), and ecdysteroid content, leading to a delay in pupa tion compared to the larvae under isolated conditions. Under crowded c onditions, a peak OA content appeared at days 2-4, followed by a peak of JHE activity at day 7, the second OA peak at day 9, and an ecdyster oid peak at day 11 of the instar. Optical stress, on the other hand, c aused an increase in OA and ecdysteroid contents, leading to an accele ration of pupation compared to controls. Whole-body OA content reached its maximum 3 days before pupation and the ecdysteroid level 2 days l ater in larvae isolated, crowded. or optically stressed. The OA conten t, JHE activity, and ecdysteroid level showed a similar pattern after pupation till adult emergence both in crowded and uncrowded animals: p eaks of OA content and JHE activity were observed at pupation, followe d by the highest peak of ecdysone 4 days later (2 days before emergenc e). The ecdysteroid levels were higher in the crowded larvae reared un der 24 h light conditions or treated with OA agonists than those in co ntrol larvae kept in the dark. Hence, isolation and optical stress inc rease OA content followed by JHE activity and ecdysteroid titer, leadi ng to changes in metamorphosis program. Some OA agonists actually had the same effect; as isolation and optical stress did, suggesting that OA is a causative agent in pupation programming of T. freemani by indu cing an increase in JHE activity, thus decreasing JH titer followed by an increase in ecdysteroid level and delayed pupation. (C) 1998 Wiley -Liss, Inc.