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Submitted to: European Journal of Entomology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/14/1996 Publication Date: N/A Citation: N/A Interpretive Summary: The development of insects is controlled by molting hormones. During the life cycle, high molting hormone titers are required at certain times (molting, egg maturation) and low molting hormone titers at other times. This is accomplished in the insect by adjustment of the balance between hormone production and hormone inactivation. Certain enzymes are vital for the production of the molting hormone. Without a sufficient quantity of the enzymes, molting and egg maturation would not be possible. In the present study we determined the changes in the activity of two similar enzymes at a critical time of larval development. The results show that only one of the enzymes is essential for the control of molting hormone production. This enzyme can now be targeted for the development of specific inhibitors, capable of blocking the growth and development of a variety of pest insect species and of providing an alternative to pest control that is both more specific and less toxic than currently used insecticides. Technical Abstract: In the mid fifth-larval-instar tobacco hornworm, Manduca sexta, the midgut has high ecdysone 20-monooxygenase (E20M0) activity, with a peak at the onset of wandering on day five. Activities of E20M0, present both in mitochondria and in microsomes, were determined around the time of the peak. During the day preceding the peak the microsomal E20M0 increased 60-fold (total activity) or 115-fold (specific activity), and it decreased to one half or less of the peak activities within two days after the peak. The mitochondrial E20M0 increased only 1.3 to 2.4-fold (total and specific activities, respectively) before the peak, but declined more rapidly than the microsomal E20M0 after the peak. It is concluded that mitochondrial and microsomal E20M0 activities are controlled independently and that changes in the physiological rate of ecdysone 20-hydroxylation are effected primarily by changes of the microsomal E20M0 activities. |
