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PLP 3104 Fundamentals of entomology Internal systems of an insect Dr. Lau Wei Hong Department of Plant Protection Faculty of Agriculture UPM Digestive system http://philschatz.com/biology-book/resources/Figure_28_04_06.png Foregut (stomodeum) Digestive system Mouth • Mandibles break down food into small pieces. Enzymes excreted from the mouth salivary glands will help in breaking down food and also add moisture. Pharynx • Peristalsis (rhythmic muscular contractions of the gut wall). Crop • Temporary food storage, digestion may occur as a result of salivary enzymes. Proventriculus • Tooth-like denticles that grind food particles. http://entomology.osu.edu/~bugdoc/Ent101/101Anatomy/101Anatomy_Pics/gut.TIF.JPG Stomodeal valve • Regulates the flow of food from the stomodeum to mesenteron. 1 Midgut (mesenteron) Digestive system Gastric caecum • Finger-like projection (2-10), provide extra surface area for secretion of enzymes or absorption of water. Ventriculus • Primary site for enzymatic digestion of food and absorption of nutrients. • Microvilli (microscopic projections): increase surface area for nutrient absorption. • Peritrohphic membrane: protects the digestive cells without inhibiting absorption of nutrient molecules. Pyloric valve • Regulates the flow of material from mesenteron to proctodeum. Hindgut (proctodeum) Malpighian tubules • long, spaghetti-like structure • Excretory organs: remove nitrogenous wastes (principally ammonium ions, NH4+) from hemolymph. • Toxic NH4+ is converted to urea and then to uric acid by a series of chemical reactions. Ileum, colon, rectum and anus • Homeostasis, regulating the absorption of water and salts from waste products in the alimentary canal. https://sp.yimg.com/xj/th?id=OIP.M1313a80ce124374e0efa7e65292d66cdH0&pid=15.1&P=0&w=300&h=300 Respiratory system • RS is responsible for: 1. Deliver sufficient O2 to cells 2. Remove CO2 (waste product of cellular respiration) • Insects breathe passively through special openings in the side of cuticle called spiracles. 1 pair of spiracles per body segment of thorax and abdomen. • These opening lead the O2 through a complex system of tubes called trachea. • Valve: muscle that regulates air flow, contract to close spiracle, relax to open spiracle. 2 Respiratory system • Spiracle • • Tracheole: special cells at the end of each tracheal branch, provides a thin, moist interface for exchange of gasses between atmospheric air and a living cell. – Valves – Hairs that filter out dust as the air enters • – O2 dissolves in the liquid and then diffuses into the cytoplasm of an adjacent cell. – CO2 diffuses out of the cell and body through the tracheal system. Taenidia: – Cuticle that winds spirally through the membranous wall. – Prevents tracheal tube collapse under pressure. – Gives tracheal tubes the ability to flex and stretch. • Air sacs: – Store a reserve of air. – Fill and enlarge as insect breaks free of the old exoskeleton and expands a new one – molting. Circulatory system • Open system: blood is not contained within a system of vessels. • Hemolymph (blood) consists of 90% plasma (liquid) and 10% hemocytes (cells). • Functions: – Transport of nutrients and hormones – Storage of substances (amino acids) – Water reservoir – Hydrostatic pressure for movement – Protection from foreign organisms that have invaded body (immunological function) – phagocytosis and encapsulation. http://blog.inceptsaves.com/files/2011/03/Trypanophobia.jpg How does hemolymph move throughout the insect body? • Only one vessel is present in the insect circulatory system: the dorsal vessel. • The dorsal vessel acts as the heart (in the abdominal region), pumping hemolymph forward into the anterior region (in the head and thorax), where it acts as the aorta and dumps the hemolymph into the head. • It flows posteriorly and is returned to the heart via ostia, which are small slits in the heart region of the dorsal vessel designed for hemolymph uptake. NERVOUS SYSTEM Nervous • What happen when you attack the fly????? • 3 components – 1)brain central – 2)ventral nerve cord nervous system – 3)peripheral nervous system (extend outside the central nervous system to serve the limbs and organs • Each of the components consists millions of neurons 3 WHAT IS A NEURON? http://1.bp.blogspot.com/-EmcKLvxRm-Y/TbBAyh1nH4I/AAAAAAAAAOI/LLkE0dpGLh8/s1600/insect-diagram.jpg Categories of neurons Afferent (sensory) neurons – bipolar or multipolar cells – dendrites associated with sense organs or receptors. – carry information toward the central nervous system. • Nerve cell • For information transfer • Composed of – 1) dendrite (enter the cell body) – 2) cell body (nucleus found) – 3) axon( leaving the body) • Repeating unit of neuron form a nervous system • Individual nerve cells connect with one another through special junctions, called synapses. Efferent (motor) neurons – unipolar cells – conduct signals away from the central nervous system – stimulate responses in muscles and glands. A D A D BRAIN Interneurons – unipolar cells (often with several collaterals and/or branching axons) that conduct signals within the central nervous system. • Nerve cord to the head is the BRAIN • 3 pairs of ganglia region: – 1)protocerebrum: associated with vision; they innervate the compound eyes and ocelli. 2)deotocerebrum: pair lobes with sensory pathway to antennae – 3)tritocerebrum: lobes with connective to 1st ganglion of ventral nerve cord 4 VENTRAL NERVE CORD • 1) subesophageal ganglion – innervates mandibles, maxillae, and labium, hypopharynx, salivary glands, and neck muscles. • 2) thoracic ganglia – ) control locomotion by innervating the legs and wings. • 3) abdominal ganglia http://1.bp.blogspot.com/-EmcKLvxRm-Y/TbBAyh1nH4I/AAAAAAAAAOI/LLkE0dpGLh8/s1600/insect-diagram.jpg – control movements of abdominal muscles. PERIPHERAL NERVOUS SYSTEM ENDOCRINE SYSTEM 1) neuron of sensory organs (sensory neuron) 2) neuron attached to muscles (motor neuron) • Function of insect nervous system critical in insect control consists of those glandular cells, tissues, and organs whose products (hormones) supplement the rapid, short-term coordinating functions of the nervous system. HORMONE • Chemical signal sent from cells in one part of an organism to cells in another part (or parts) of the same individual. • Chemical messenger • Produced in very small quantities, but cause big changes in their target cells. • Effect may be stimulatory (pencetus) or inhibitory (perencat). http://cronodon.com/images/ant_glands_v2.jpg 5 Categories of hormoneproductin cells in insects 1) Endocrine glands -- producing hormones and releasing them into the circulatory system. 2) Neurohemal organs -- store their secretory product in a special chamber until stimulated to release it by a signal from the nervous system (or another hormone). 3) Neurosecretory cells -- specialized nerve cells (neurons) that respond to stimulation by producing and secreting specific chemical messengers. - a link between the nervous system and the endocrine system Endocrine glands • the largest glands are found in the prothorax: PROTORACIC GLANDS (A) • Produce ecdysteroids/ molting hormones(ECDYSONE) • stimulate synthesis of chitin and protein in epidermal cells for MOULTING PROCESS • Once reaches adult stage, its prothoracic glands wither (kering/kecut): (A) • never molt again. (A) 4) Internal organs -- hormone-producing cells are associated with organs like ovaries and testes, the fat body, and parts of the digestive system Neurohemal organs Neurosecretory cells (D) • 1) CORPORA CARDIACA (B) – Release prothoracicotropic hormone (PTTH) – Only release PTTH when received signal from brain. • 2) CORPORA ALLATA (C) – manufacture juvenile hormone (JH), – Inhibits the development of adult characteristics during the immature stages – promotes sexual maturity (B)(C) during the adult stage. • found in clusters, both medially and laterally in the insect's brain. • specialized nerve cells (neurons) that respond to stimulation by producing and secreting specific chemical messengers. Functionally, they serve as a link between the nervous system and the endocrine system • secrete brain hormone. (D) (D) (D) (B)(C) Internal organs • Ovaries and testes – produce gonadal hormones: to coordinate courtship and mating behaviors. • Ventral ganglia in the nervous system – eclosion hormone that helps an insect shed (tanggal) its old exoskeleton – bursicon hormone: that causes hardening and tanning of the new one. http://www.dinkuminteractive.com/wp-content/uploads/2011/05/End.jpg 6