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INSECT AND THEIR ROLES Akanksha Humane* and Rekha Samrit1 Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola-444104, Maharashtra, India. 1Mahatma Phule Krishi Vidyapeeth, Rahuri-413722 Maharashtra, India. * Corresponding author- [email protected] Received: July 27, 2020; Accepted: Aug 18, 2020

Introduction Hormones are chemicals produced by an organism which circulate in blood to regulate its long term physiological, developmental and behavioural activities. hormones are generated and used by to regulate physiological, developmental and behavioural events. Insect hormones can be produced by epithelial glands. Growth and development in insects control by series of hormones which are secreted in predetermine sequences. Prothoracicotropic (PTTH) was the first insect hormone to be discovered by early workers such as Stefan Kopec in 1922 and Vincent Wigglesworth in 1934 as “Brain hormone”. Endocrine Glands in Insects

Glands Secretions Neurosecretory cells Produce Neurosecreation. Prothoracic gland Produce Ecdysone. Corpora allata Produce JH. Stores and release brain hormones. Corpora cardiaca Also produces and releases some peptides such as Adipokinetic Hormones. Midgut endocrine cells Produce various peptides. Produce the ecdysis triggering hormone Epitracheal gland “Ecdysion” in Lepidoptera.

Neurosecretory Hormones (Brain Hormone) Brain Hormone  NSC in dorsal part of protocerebrum produce a hormone called Prothoracicotropic Hormone (PTTH) or BRAIN HORMONE which activates prothoracic glands.  Mostly this hormone is constituted of lipid or peptide and water soluble polypeptide or small molecule of protein.

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Fig.1: Insect possess Hormones that Effect Bursicon  Neurosecretory hormone that controls tanning or sclerotization and mechanical properties of the cuticle during and after a moult.  Bursicon, commonly found in neurohaemal organs associated with the ventral chain ganglia is suggested to stimulate tanning and sclerotisation of the cuticle following ecdysis. Diuretic Hormone  Neurosecretory cells scattered in the ventral nerve cord produce diuretic hormone.  It involved in regulation of insect water balance. Functional Significance of Neurosecretory Hormones  The secretions of the median neurosecretory cells promote the functioning of the prothoracic glands stimulate protein synthesis, probably control water loss and oocyte development activities.  Neurosecretory hormones have also been associated with behavioural activities, such as, response of the female towards the malecocoon formation etc. Hormones from Corpora Cardiaca  Corpora cardiaca found in most insects except collembola, which lies on each sides of aorta behind brain.  It acts as a Conventional storage and release organ for neurohormones.

1. Adipokinetic Hormone(s): Adipokinetic hormone (AKH), a decapeptide from the locust has been identified. AKH in corpora cardiaca of locusts regulates lipid metabolism during prolonged flight.

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2. Neurohormone D: Material isolated from corpora cardiaca of Caracius morosus called Neurohormone D, which increasing the frequency of amplitude of heart beat, stimulating colour change in Caracius. 3. Chloride-Transport stimulating hormone: In desert locust rectum of insect is an important organ, which regulates the ionic balance. It is stimulated by the hormone from corpora cardiaca, the Chloride- Transport stimulating hormone. Juvenile Hormone / Neotinin  Corpora allata secretes Juvenile hormone (JH) or Neotinin, there by inhibit metamorphosis. This CA hormone(s) is therefore sometimes also called as “Inhibitory or Status Quo” hormone.  Corpora allata glands were discovered by JANET during 1899.  JH first extracted from the abdomen of Hyalophora cercopia (Moth). Functional Significance of Juvenile Hormones  It is needed for egg maturation and function as accessory glands in male.  Other activities controlled by this hormone are polymorphism, regeneration, metabolism of fat, water balance, colour changes, imaginal diapause, pheromone production etc. Ecdysone / Moulting Hormone /Ecdysteriod  Neurosecretory cells activate prothoracic glands to secrete ECDYSONE.  First experimental proof about the importance of Prothoracic glands was provided by a Japanese worker, Fukuda in 1940 while working with silkworm.  Ecdysteriods are produced by the prothoracic gland, in immature insects, and by the gonads, in adults. In insects, insulin-producing cells are found throughout the body, including in the pars intercerebralis region in the brain. In many insects, the insulin- producing cells in the brain are connected to nearby glands that produce other hormones, including JH (Wu and Brown, 2006). Functional Significance of Ecdysone  It initiates the moulting process.  It breaks larval and pupal diapauses.  Renewals of growth and deposition of new cuticle.  MH is interference in principal enzyme system, regulate normal metabolism and growth. Ex. Cytochrome oxidase.  It influences the puffing pattern of giant cell in & Chironomous.  It inhibits the function of Corpora allata. Other Hormones Peptide Hormones It is known to control wide range of physiological, Biochemical and Developmental function including water balance, lipid and carbohydrate metabolism, muscle contraction, reproduction, growth and development.

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Proctolin:  Isolated from Periplanata americana. It acts as an Excitatory Neurotransmitter to modulate muscle excitability.  Functions of endocrine hormones.  Regulation of moulting.  Determination of form at metamorphosis.  Polymorphism.  Regulation of diapause.  Involvement in reproduction.  Regulation of metabolic activities and general body functions.  Regulation of behaviour. Conclusion The insect hormones have the developmental, physiological and behavioural effects in the same insect. These are important for moulting and reproduction of insect.The results of hormone action may appear remarkably diverse in different species.It have been the target site for IGRs, viz., JH analogues, chitin synthesis inhibitors, and ecdysone agonists and used in the diverse pest management programs. Reference Wu Q and Brown MR. (2006). Signaling and function of insulin-like peptides in insects. Annual Review of Entomology 51:1-24.

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