Juvenile hormone

Juvenile hormones (JHs) are a group of acyclic sesquiterpenoids that regulate many aspects of insect physiology.

[1][2][3] In insects, JH (formerly neotenin) refers to a group of hormones, which ensure growth of the larva, while preventing metamorphosis.

Juvenile hormones are secreted by a pair of endocrine glands behind the brain called the corpora allata.

[6] Certain species of crustaceans have been shown to produce and secrete methyl farnesoate, which is juvenile hormone III lacking the epoxide group.

The level gradually decreases during the development of the insect, allowing it to proceed to successive instars with each molt.

In this study, two adult Rhodnius had their blood systems linked, ensuring that the JH titre in both would be equal.

Generally, the removal of the corpora allata from juveniles will result in a diminutive adult at the next moult.

[16] In adult honey bees, JH and Vitellogenin titers in general show an inverse pattern.

[21] During the first 15 days, workers perform tasks inside the hive, such as nursing larvae, constructing comb, and cleaning cells.

[25] The unique negative relationship between JH and Vitellogenin may be important to the understanding of queen longevity.

[26] JH in many butterfly and moth species are necessary for the production and release of the sex pheromone by females.

One JH analogue, methoprene, is approved by the WHO for use in drinking water cisterns to control mosquito larvae due to its exceptionally low toxicity (LD50 >35,000 mg/kg in the rat).

JH is principally degraded by the enzymes juvenile-hormone esterase (JHE) or juvenile hormone epoxide hydrolase (JHEH).

There are a large number of additional steps to generate cholesterol from IPP, the ubiquitous precursor of all isoprenoids.

The enzymes of this pathway were first studied in Manduca sexta, which produces both homoisoprenoid and isoprenoid (JHIII) JHs.

[36] Lee et al. showed that the same source of enzymes efficiently make both mevalonate and its 3-ethyl homolog, homomevalonate.

Thus, this part of the isoprenoid pathway appears nearly identical with that of cholesterol with the exception of the insect specific homoisoprenoid units.

[40] Absolute configuration of homomevalonate and 3-hydroxy-3-ethylglutaryl and 3-hydroxy-3-methylglutaryl coenzyme a, produced by cell-free extracts of insect corpora allata.

A cautionary note on prediction of absolute stereochemistry based on liquid chromatographic elution order of diastereomeric derivatives.

While the vast majority of farnesyl diphosphate is converted into ultimately cholesterol in animals, in insects it is apparently acting on by a diphosphatase to give farnesol, which in turn is acted on by an NAD+ dependent enzyme, farnesol/farnesal dehydrogenase in M. sexta[40] to give farnesoic acid.

Subsequent work has shown that the enzyme is highly specific for trans allylic alcohols with at least three isoprene units,[42] and to also be present in mosquitoes.

[44] A recent publication by Nouzova et al. (2015) shows that allatostatin C, the peptide which inhibits JH production by the corpora allata, blocks the transport of citrate out of the mitochondrion in Aedes aegypti.