Ch10 Insect hormones

• Insects have a high impact on human life.
• Insect hormones are understood by understanding how insects function.
• Insects have a unique combination of characteristics including an exoskeleton for ecdysis, metamorphosis for niche differentiation, open circulation through hemolymph, excretion through Malpighian tubules, respiratory system through tracheal tubes, small body size, arthropoda for jointed appendages, ability to fly with two pairs of wings (adult), high reproductive capacity, and adaptability in a changing environment.
• Hormones control various processes in insects including development and growth, reproduction, energy metabolism, water and ion balance, and more, which is similar to the situation in vertebrates.
• Insect hormones are found in the central nervous system, glandular part of corpora cardiaca (CCg), corpora allata (CA, juvenile hormone), prothoracic gland (PG, ecdysteroids), intestine (enteroendocrine cells), gonads, epitracheal glands (Inka cells), and more.
• In insects, stored lipid droplets lead to lipolysis, which increases β oxidation in the fat body and increases the availability of fatty acids for the flight muscles.
• The physiological roles of Adipokinetic Hormone(s) in insects include the regulation of energy metabolism, complex functional interactions with other metabolic regulation pathways, behavioral effects, such as starvation-induced hyperactivity, regulation of immune and stress responses, effects on reproduction, and stimulation of heart and other muscular contractions.
• Hypertrehalosemic and adipokinetic hormones (HTH, AKH) are major energy recruitment hormones in insects.
• Triacylglycerol is converted to diacylglycerol (DAG) during insect flight.
• Glycogen is converted to trehalose (and glucose) during insect flight.
• Major energy recruitment is needed for insect flight, including the initial use of glycogen stores in the fat body and the use of lipid (triacylglycerol) stores in the fat body for sustained flight.
• DAG is transported to the flight muscles in insects, coupled to lipophorins (Lp).
• The role of adrenaline in vertebrates is to increase heart rate and blood pressure.
• Adipokinetic Hormone(s) in insects are produced in the glandular part of the corpora cardiaca (APCs) or IPCs.
• Types of hormones in insects include steroid hormones (ecdysteroids), sesquiterpenes (juvenile hormones), peptide/protein hormones (prothoracicotropic hormone (PTTH), allatotropin (AT), adipokinetic hormone (AKH), ecdysis-triggering hormone (ETH), CRF-like and calcitonin-like diuretic hormones, insulin-like peptides (ILPs), etc.).
• Insect hormones are involved in the secretion of molting fluid and new cuticle.
• Ecdysteroid biosynthesis involves 20E, cholesterol/phytosterols, and is induced by ProThoracicoTropic Hormone (PTTH).
• An old diagram of insect metamorphosis includes insect hormones.
• Conversion from E to 20E occurs in different peripheral tissues.
• Cell division in the epidermis is regulated by insect hormones.
• Ecdysteroids are produced in prothoracic glands and also in gonads.
• 50 identified insect neuropeptide families, with many initial discoveries in locusts, and most of these are acting via G protein-coupled receptors (GPCRs).
• Insect hormones are species-dependent.
• Juvenile hormone, JH, determines changes in internal morphology and its timing modulates the action of 20E.
• Molting hormone, 20E, peaks prior to each molt.
• The most important ecdysteroids are ecdysone (E) and 20-hydroxyecdysone (E is converted to 20E in peripheral tissues).
• Insect hormones are involved in post-embryonic development.
• Ecdysteroids are precursors to dietary sterols such as cholesterol (animal diet) or campesterol & β-sitosterol (vegetal diet).
• Insect hormones cause structural changes in internal organs.
• Amines such as octopamine and serotonin (5HT) are also found in insect hormones.
• Neuropeptides are involved in the control of a wide variety of physiological processes in insects including energy metabolism, osmoregulation, and mating behavior.
• The onset of metamorphosis from larval to adult form requires cessation of JH production and clearance of remaining JH from hemolymph by specific enzymes.
• • Juvenile hormone signaling is a key target in insect pest control.
• Action via binding to nuclear receptors: EcR-A, EcR-B1, EcR-B2 (receptor isoforms), EcRs form heterodimers with USP (ultraspiracle, homolog of vertebrate receptor RXR).
• Juvenile hormones (JHs) are sesquiterpenoids produced in the corpora allata, with six major forms identified: 16-19 carbon skeleton.
• Major role in post-embryonic development: stimulation of the molting process by activation/inactivation of specific genes.
• Produced in neurosecretory cells of the brain, the active form of PTTH is a homodimer.
• Juvenile hormone biosynthesis involves acetyl-CoA, corpora allata (CA), and is regulated by allatostatins, allatotropins, nutrients, insulin-like peptides, neurotransmitters.
• Juvenile hormone signaling is a key target in insect pest control.
• In some insects, ecdysone production is inhibited by "ecdysiostatic hormone(s)" from the CNS.