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Induction of dauer pupae by fenoxycarb in the silkworm, Bombyx mori
S G. Dedos1, F Szurdoki, A Székács
1Department of Biological Production, Tokyo University of Agriculture and Technology, Fuchu-shi, 183, Tokyo, Japan
Abstract:
Topical application of fenoxycarb (1 &mgr;g per animal) at 129 or 132 h of the fifth instar larvae of the silkworm, Bombyx mori, did not induce morphological abnormalities in the pupal stage, but these animals became dauer (permanent) pupae. This condition of B. mori and the endocrine events leading to permanent pupae are discussed in this work. Application of fenoxycarb at 132 h of the fifth instar elicited a high ecdysteroid titre in the pharate pupal stage and a steadily high ecdysteroid titre in the pupal stage. The fenoxycarb-induced permanent pupae had non-degenerating prothoracic glands that secreted low amounts of ecdysteroid and did not respond to recombinant prothoracicotropic hormone (rPTTH) late in the pupal stage. The Bombyx PTTH titre in the haemolymph, determined by a time-resolved fluoroimmunoassay, was lower than that of controls at the time of pupal ecdysis, but higher than controls later in the pupal stage in fenoxycarb-treated animals. After application of fenoxycarb, its haemolymph level, measured by ELISA, reached a peak at pupal ecdysis, then remained low. These results suggest that the fenoxycarb-mediated induction of permanent pupae is only partially a brain-centred phenomenon. It also involves alterations in the hormonal interplay that govern both the initiation of pupal-adult differentiation and changes in the steroidogenic pathway of the prothoracic glands of B. mori.
Insights
Fenoxycarb application causes permanent pupae in silkworms (Bombyx mori) by altering hormonal signals. This disrupts normal development, affecting prothoracic glands and ecdysteroid levels, indicating a complex endocrine regulation.
Area of Science:
- Insect endocrinology
- Developmental biology
- Chemical toxicology
Background:
- Fenoxycarb is an insect growth regulator.
- Insect metamorphosis is regulated by hormones like ecdysteroids and PTTH.
- Understanding endocrine disruption is crucial for pest control and developmental studies.
Purpose of the Study:
- To investigate the effects of fenoxycarb on Bombyx mori development.
- To elucidate the endocrine mechanisms underlying fenoxycarb-induced permanent pupae.
- To analyze hormonal changes and prothoracic gland function.
Main Methods:
- Topical application of fenoxycarb to fifth instar Bombyx mori larvae.
- Monitoring of morphological development and pupal stage.
- Measurement of ecdysteroid and PTTH titers in hemolymph using ELISA and time-resolved fluoroimmunoassay.
- Assessment of prothoracic gland activity and response to rPTTH.
Main Results:
- Fenoxycarb induced permanent pupae without morphological abnormalities.
- Elevated ecdysteroid titers were observed in pharate and pupal stages.
- Prothoracic glands showed reduced responsiveness to rPTTH, despite low ecdysteroid secretion.
- PTTH hemolymph levels were altered, with initial decrease and later increase compared to controls.
- Fenoxycarb levels peaked at pupal ecdysis and then decreased.
Conclusions:
- Fenoxycarb-induced permanent pupae result from complex endocrine alterations.
- The phenomenon is partially brain-centered but also involves direct effects on prothoracic gland function.
- Fenoxycarb disrupts the hormonal interplay regulating pupal-adult differentiation and steroidogenesis.