Juvenile hormone

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In insects, juvenile hormone (also neotenin) refers to a group of hormones which ensure growth of the larva, while preventing metamorphosis. It is secreted by a pair of endocrine glands behind the brain called the corpora allata. Juvenile hormone is also important for the production of eggs in female insects. Most insect species contain only juvenile hormone (JH) III. To date JH 0, JH I, and JH II have been identified only in the Lepidoptera (butterflies and moths). The form JHB3 (JH III bisepoxide) appears to be the most important JH in the Diptera, or flies.

Contents 1 Control of development 2 Use as an insecticide 3 Forms 4 References

[edit] Control of development

The titre of JH found in the haemolymph of the developing insect controls the stage of development that the insect is in. During ecdysis the form of the new cuticle laid down before the next moult is controlled by the JH level in the insect. JH maintains a juvenile state, and so the level of it gradually decreases during the development of the insect, allowing it to proceed to successive instars with each moult.

This has been demonstrated in various studies, most prominently that by V. B. Wigglesworth. In this two adult Rhodnius had their blood systems linked, ensuring that the JH titre in both would be equal. One was a third instar Rhodnius, the other was a fourth instar. When the corpora allata of the third instar insect were removed, the level of JH was equal in both insects to that in the fourth instar animal, and hence both proceeded to the fifth instar at the next moult. When the fourth instar Rhodnius had its corpora allata removed, both contained a third instar level of JH and hence one proceeded to instar four, and the other remained at this instar.

Generally, the removal of the corpora allata from juveniles will result in a diminutive adult at the next moult. Implantation of corpora allata into last larval instars will boost JH levels and hence produce a supernumary (extra) juvenile instar.

[edit] Use as an insecticide

Synthetic analogues of the juvenile hormone are used as an insecticide, preventing the larvae from developing into adult insects. At high levels of JH, larva can still molt, but the result will only be a bigger larva, not an adult. Thus the reproductive cycle is broken. One insecticide, methoprene, is approved by WHO for use in drinking water cisterns to control mosquito larvae.

[edit] Forms

• Juvenile hormone 0
  • CAS methyl (2E,6E)-10R,11S-(oxiranyl)-3,7-diethyl-11-methyl-2,6-tridecadienoate
  • Formula: C₁₉H₃₂O₃
• Juvenile hormone I
  • CAS methyl (2E,6E)-10R,11S-(oxiranyl)-7-ethyl-3,11-dimethyl-2,6-tridecadienoate
  • Formula: C₁₈H₃₀O₃
• Juvenile hormone II
  • CAS methyl (2E,6E)-10R,11S-(oxiranyl)-3,7,11-trimethyl-2,6-tridecadienoate
  • Formula: C₁₇H₂₈O₃
• Juvenile hormone III
  • CAS methyl (2E,6E)-10R-(oxiranyl)-3,7,11-trimethyl-2,6-dodecadienoate
  • Formula: C₁₆H₂₆O₃
• Juvenile hormone JHB3
  • CAS methyl (2E,6E)-6S,7S,10R-(dioxiranyl)-3,7,11-trimethyl-2,6-dodecadienoate
  • Formula: C₁₆H₂₆O₄

[edit] References

• Wigglesworth, VB. (1964) The hormonal regulation of growth and reproduction in insects. Adv. Insect Physiol. 2: 247-336
• Wigglesworth, VB. (1939) The Principles of Insect Physiology. Cambridge Univ. Press. Cambridge.