Ryuko Takeya

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).

Abstract 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.

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-hormone esterase (JHE), and ecdysteroid content, leading to a delay in pupation compared to the larvae under isolated conditions. Under crowded conditions, 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 ecdysteroid peak at day 11 of the instar. Optical stress, on the other hand, caused an increase in OA and ecdysteroid contents, leading to an acceleration of pupation compared to controls. Whole-body OA content reached its maximum 3 days before pupation and the ecdysteroid level 2 days later in larvae isolated, crowded, or optically stressed. The OA content, JHE activity, and ecdysteroid level showed a similar pattern after pupation till adult emergence both in crowded and uncrowded animals: peaks of OA content and JHE activity were observed at pupation, followed by the highest peak of ecdysone 4 days later (2 days before emergence). The ecdysteroid levels were higher in the crowded larvae reared under 24 h light conditions or treated with OA agonists than those in control larvae kept in the dark. Hence, isolation and optical stress increase OA content followed by JHE activity and ecdysteroid titer, leading 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 inducing an increase in JHE activity, thus decreasing JH titer followed by an increase in ecdysteroid level and delayed pupation. Arch. Insect Biochem. Physiol. 37:34–46, 1998.

Effect of larval density on whole-body biogenic amine levels of Tribolium freemani hinton

Abstract 1. Various biogenic amines, their precursors and metabolites in gregarious and solitary forms of the flour beetle Tribolium freemani Hinton larvae were measured using high-performance liquid chromatography coupled with electrochemical detection. 2. Octopamine was much more abundant than dopamine, serotonin, epinephrine, norepinephrine and related substances, suggesting that octopamine may play much more important roles in growth and behaviour of T. freemani than other biogenic amines and related substances. 3. Octopamine levels were higher in gregarious forms than solitary forms of T. freemani larvae, and the relation between octopamine content, hormone cycles and motility is discussed.