Juvenile hormone
Encyclopedia
Juvenile hormones are a group of acyclic sesquiterpenoids that regulate many aspects of insect physiology
Insect physiology
Insect physiology includes the physiology and biochemistry of insect organ systems.Although diverse, insects are quite similar in overall design, internally and externally...

. JHs regulate development, reproduction, diapause
Diapause
Diapause is the delay in development in response to regularly and recurring periods of adverse environmental conditions. It is considered to be a physiological state of dormancy with very specific initiating and inhibiting conditions...

, and polyphenism
Polyphenism
A polyphenic trait is a trait for which multiple, discrete phenotypes can arise from a single genotype as a result of differing environmental conditions.-Definition:A polyphenism is a biological mechanism that causes a trait to be polyphenic...

s.

In insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s, JH (formerly called neotenin) refers to a group of hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

s, which ensure growth of the larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

, while preventing metamorphosis. Because of their rigid exoskeleton, insects grow in their development by successively shedding their exoskeleton (a process known as molting).

Juvenile hormones are secreted
Secretion
Secretion is the process of elaborating, releasing, and oozing chemicals, or a secreted chemical substance from a cell or gland. In contrast to excretion, the substance may have a certain function, rather than being a waste product...

 by a pair of endocrine glands behind the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

 called the corpora allata
Corpus allatum
The corpus allatum , in insect physiology, is an endocrine gland which generates juvenile hormone; as such, it plays a crucial role in metamorphosis. Surgical removal of the corpora allata can cause an immature larva to pupate at its next molt, resulting in a miniature adult...

. JHs are also important for the production of eggs in female insects.

JH was discovered in 1965 and the molecular structure
Molecular structure
The molecular structure of a substance is described by the combination of nuclei and electrons that comprise its constitute molecules. This includes the molecular geometry , the electronic properties of the...

 solved in 1967.

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
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...

 (butterflies and moths). The form JHB3 (JH III bisepoxide) appears to be the most important JH in the Diptera
Diptera
Diptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...

, or flies.
Certain species of crustaceans have been shown to produce and secrete methyl farnesoate, which is juvenile hormone III lacking the epoxide group. Methyl farnesoate is believed to play a role similar to that of JH in crustaceans.

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
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...

 the form of the old cuticle laid down before the next moult is controlled by the JH level in the insect. JH maintains a juvenile state. The level of it gradually decreases during the development of the insect, allowing it to proceed to successive instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...

s with each molt.

This has been demonstrated in various studies, most prominently that by V. B. Wigglesworth in 1960s. In this study, two adult Rhodnius
Rhodnius
Rhodnius is a genus of bugs in the subfamily Triatominae, important vectors of Chagas disease. They were important models for Sir Vincent Wigglesworth's studies of insect physiology, specifically growth and development.-Species:...

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
Diminutive
In language structure, a diminutive, or diminutive form , is a formation of a word used to convey a slight degree of the root meaning, smallness of the object or quality named, encapsulation, intimacy, or endearment...

 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 etc.

Juvenile hormones in honey bee
Honey bee
Honey bees are a subset of bees in the genus Apis, primarily distinguished by the production and storage of honey and the construction of perennial, colonial nests out of wax. Honey bees are the only extant members of the tribe Apini, all in the genus Apis...

s

There is a complex interaction between JH, the hormone ecdysone
Ecdysone
Ecdysone is a steroidal prohormone of the major insect molting hormone 20-hydroxyecdysone, which is secreted from the prothoracic glands. Insect molting hormones are generally called ecdysteroids. Ecdysteroids act as moulting hormones of arthropods but also occur in other related phyla where they...

 and vitellogenin
Vitellogenin
Vitellogenin is a synonymous term for the gene and the expressed protein. The protein molecule is classified as a glycolipoprotein, having properties of a sugar, fat and protein...

. In the development stage, as long as there is enough JH, the ecdysone promotes larva-to-larva molts. With lower amounts of JH, ecdysone promotes pupation. Complete absence of JH results in formation of the adult.
In adult honey bees, JH and Vitellogenin
Vitellogenin
Vitellogenin is a synonymous term for the gene and the expressed protein. The protein molecule is classified as a glycolipoprotein, having properties of a sugar, fat and protein...

 titers in general show an inverse pattern.

JH titers in worker honey bees
Worker bee
A Worker bee is any female eusocial bee that lacks the full reproductive capacity of the colony's queen bee; under most circumstances, this is correlated to an increase in certain non-reproductive activities relative to a queen, as well...

 progressively increase through the first 15 or so days of the worker's life before the onset of foraging.
During the first 15 days, workers perform tasks inside the hive
Beehive (beekeeping)
A beehive is an enclosed structure in which some honey bee species of the subgenus Apis live and raise their young. Natural beehives are naturally occurring structures occupied by honeybee colonies, while domesticated honeybees live in man-made beehives, often in an apiary. These man-made...

, such as nursing larvae, constructing comb, and cleaning cells. JH titers peak around day 15; workers this age guard, remove dead bees from the colony, and fan at the colony entrance to cool the nest. Aggressiveness of guard bees is correlated with their blood JH levels. Even though guards have high JH levels, their ovaries are relatively undeveloped. Although, JH does not activate foraging. Rather it is involved in controlling the pace at which bees develop into foragers.

Vitellogenin titers are high at the beginning of adult life and slowly decrease.

JH has been known to be involved in the queen-worker caste differentiation during the larval stage. The unique negative relationship between JH and Vitellogenin may be important to the understanding of queen longevity.

See also Bee learning and communication
Bee learning and communication
Honey bees learn and communicate in order to find food sources and for other means.-Learning:Learning is essential for efficient foraging. Honey bees are unlikely to make many repeat visits if a plant provides little in the way of reward...


Forms

  • Methyl farnesoate
    • CAS
      Chemical Abstracts Service
      Chemical Abstracts is a periodical index that provides summaries and indexes of disclosures in recently published scientific documents. Approximately 8,000 journals, technical reports, dissertations, conference proceedings, and new books, in any of 50 languages, are monitored yearly, as are patent...

       methyl (2E,6E)-3,7,11-trimethyl-2,6,10-dodecatrienoate
    • Formula: C16H26O2

  • Juvenile hormone 0 (found in Lepidoptera)
    • CAS
      Chemical Abstracts Service
      Chemical Abstracts is a periodical index that provides summaries and indexes of disclosures in recently published scientific documents. Approximately 8,000 journals, technical reports, dissertations, conference proceedings, and new books, in any of 50 languages, are monitored yearly, as are patent...

       methyl (2E,6E)-10R,11S-(oxiranyl)-3,7-diethyl-11-methyl-2,6-tridecadienoate
    • Formula: C19H32O3

  • Juvenile hormone I (found in Lepidoptera)
    • CAS
      Chemical Abstracts Service
      Chemical Abstracts is a periodical index that provides summaries and indexes of disclosures in recently published scientific documents. Approximately 8,000 journals, technical reports, dissertations, conference proceedings, and new books, in any of 50 languages, are monitored yearly, as are patent...

       methyl (2E,6E)-10R,11S-(oxiranyl)-7-ethyl-3,11-dimethyl-2,6-tridecadienoate
    • Formula: C18H30O3

  • Juvenile hormone II (found in Lepidoptera)
    • CAS
      Chemical Abstracts Service
      Chemical Abstracts is a periodical index that provides summaries and indexes of disclosures in recently published scientific documents. Approximately 8,000 journals, technical reports, dissertations, conference proceedings, and new books, in any of 50 languages, are monitored yearly, as are patent...

       methyl (2E,6E)-10R,11S-(oxiranyl)-3,7,11-trimethyl-2,6-tridecadienoate
    • Formula: C17H28O3

  • Juvenile hormone III
    • CAS
      Chemical Abstracts Service
      Chemical Abstracts is a periodical index that provides summaries and indexes of disclosures in recently published scientific documents. Approximately 8,000 journals, technical reports, dissertations, conference proceedings, and new books, in any of 50 languages, are monitored yearly, as are patent...

       methyl (2E,6E)-10R-(oxiranyl)-3,7,11-trimethyl-2,6-dodecadienoate
    • Formula: C16H26O3

  • Juvenile hormone JHB3 (found in diptera)
    • CAS
      Chemical Abstracts Service
      Chemical Abstracts is a periodical index that provides summaries and indexes of disclosures in recently published scientific documents. Approximately 8,000 journals, technical reports, dissertations, conference proceedings, and new books, in any of 50 languages, are monitored yearly, as are patent...

       methyl (2E,6E)-6S,7S,10R-(dioxiranyl)-3,7,11-trimethyl-2-dodecaenoate
    • Formula: C16H26O4

Use as an insecticide

Synthetic analogues of the juvenile hormone are used as an insecticide
Insecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...

, preventing the larvae from developing into adult insects. JH itself is expensive to synthesize and is unstable in light. At high levels of JH, larva can still molt, but the result will only be a bigger larva, not an adult. Thus the insect's reproductive cycle is broken. One JH analogue, methoprene
Methoprene
Methoprene is a juvenile hormone analog which can be used as an insecticide that acts as a growth regulator. Methoprene is an amber-colored liquid with a faint fruity odor which is essentially nontoxic to humans when ingested or inhaled. It is used in drinking water cisterns to control mosquitoes...

, is approved by the WHO
Who
Who may refer to:* Who , an English-language pronoun* who , a Unix command* Who?, one of the Five Ws in journalism- Art and entertainment :* Who? , a 1958 novel by Algis Budrys...

 for use in drinking water cistern
Cistern
A cistern is a waterproof receptacle for holding liquids, usually water. Cisterns are often built to catch and store rainwater. Cisterns are distinguished from wells by their waterproof linings...

s to control mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...

 larvae.

Juvenile hormone regulation

Juvenile hormone is produced in the corpora allata of insects. JH will disperse throughout the haemolymph and act on responsive tissues. JH is principally degraded by the enzymes Juvenile-hormone esterase
Juvenile-hormone esterase
In enzymology, a juvenile-hormone esterase is an enzyme that catalyzes the chemical reactionThe 3 substrates of this enzyme are methyl, --10,11-epoxy-3,7,11-trimethyltrideca-2,6-dienoate, and H2O, whereas its two products are --10,11-epoxy-3,7,11-trimethyltrideca-2,6-dienoate and methanol.This...

 (JHE) or juvenile hormone epoxide hydrolase (JHEH). JHE and JHEH both lead to suppression of JH signaling and response. Tissues responsive to JH may produce one or both of these enzymes.

JH stimulates the accessory glands of adult males, promoting gland growth and the production of accessory gland secretion. Yolk production (vitellogenesis
Vitellogenesis
Vitellogenesis is the process of yolk formation via nutrients being deposited in the oocyte, or female germ cell involved in reproduction. It starts when the fat body stimulates the release of juvenile hormones and produces vitellogenin protein. It occurs in all animal groups lower than the mammals...

) in female ovaries is also stimulated by JH action. JH may also regulate reproductive behaviour in both sexes.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK