Introduction to the Class Insecta

Mohamed Ben Rashed MBBCh, DCH, DTCH, Msc, PhD Clinical Parasitology and Medical Entomology Department Medical Faculty / Alfatah University Tripoli/Libya First Edition Preface I am presenting this book , to become as a reference for medical students of third class, the teaching members of this field and the busy physician, I have prepared this synopsis in the hope that it will convey the correct , and modern information of medical entomology . I exert my best efforts to collect and to add of the best benefit from various modern books and references, most of it from the internet, to present this book in a complete Image. Iam sorry for any incompletion or non clear of any part, but certainly I will correct that in the coming edition. In intended more explaining in some of the diseases such as Plaque, Scabies, Myiasis and others, because these are the most important and dangerous diseases transmitted or caused by arthropoda which can leads to high rate of morbidity and mortality in the community . I wrote this to be an easy scientific reference to the student, that because I found many of them suffering and asking of non availability of any specific comprehensive reference covering their needs, also due to the expensive price of the references. And the contradictions of the teaching members on the priority of teaching, this happened in the different medical faculties in the Jamahirya. Mohamed Ben Rashed Acknowledgments Acknowledgments to Centers for Disease Control and Prevention , Division of Parasitic Diseases , for prevention to copy photographs. I also acknowledge with gratitude the assistance received from : Dr- Nabile Jabr, head of parasitology department / Medical faculty/ Banha university; Egypt, for his effort to revise the book. The Auther Contents Preface Acknowledgments Introduction Phylum Arthropoda Features of Arthropods General arthropods morphology The arthropoda and its ways can affect our health Class Insecta Order: Diptera (true flies) Biting flies Mosquitoes Simulium:Black fly Chrysops:Horse fly Stomoxys calcitrans:Stable fly Glossina: tsetse fly Phlebotomus/Lutozomiay:Sand fly Culicoides: Midges Non-biting flies Filth flies Musca vetstissima:Bush fly Musca domestica: House fly Myiasis Order: Dictyoptera Cockroaches Order: Coleoptera Beetles Order: Hymenoptera Ants, Bees, Wasps Order: Siphonptera Fleas Plaque Sandflea Order: Anoplura Lice Order: Hemiptera Cimicidae:Bed bugs Triatominae:Assassin bugs Class:Arachnides Order: Acarina or Acari Ticks Mites Scabies Order : Araneida Spiders Order Scorpionida Scorpions Class Myriapoda Order:Diplopoda:Millipedes Order: Chilopoda:Centipedes Class Crustacea:Cyclopes Phylum Pentastoma:Linguatula serrata Terms and words meanings References Introduction The discipline of medical entomology, or public health entomology, is focused upon insects and arthropods that impact human health. It include the insects of medical importance. An arthropod phylum is an invertebrate animal having an exoskeleton (external skeleton), a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda (from Greek arthron, "joint", and podos "foot", which together mean "jointed feet". Arthropods are characterized by their jointed limbs and cuticles, which are mainly made of α-chitin. The rigid cuticle inhibits growth, so arthropods replace it periodically by molting. The arthropods constitute an extremely diverse numbers of species .Most species are ectoparasites. Some species are directly responsible for morbidity and mortality of their hosts. Many arthropods serve additionally as intermediate hosts for helminth parasites, or vectors for serious protozoan, bacterial, or viral diseases. Note: The phylum Arthropoda are divided into five classes. The class Insecta and Arachnida include most of the parasitic species or vectors of disease. The class Myriapoda have only the poisonous millipedes and centipedes, the Crustacea class contain few species that serve as intermediate host for animal parasites. The Onychophora class are not injurious. Features of Arthropods • Exoskeleton - a hard protective covering around the outside of the body (divided by sutures into plates called sclerites) • Segmented body - that allows movement • Jointed limbs and jointed mouthparts - that allow extensive specialisation • Bilateral symmetry - whereby a central line can divide the body into two identical halves, left and right • Ventral nerve chord - as opposed to a vertebrate nerve chord which is dorsal • Dorsal blood vessel. General arthropods morphology Insects such as flies, wasps and cockroaches all have • 3 body segments • 6 legs • 1 pair antennae Arachnids include spiders, scorpions, ticks and mites. They all have • 2 body segments - cephalothorax and abdomen • 8 legs • no antennae Head The insect head is a sclerotised capsule of mainly rigid sclerites. It houses the compound eyes, simple eyes (ocelli), antennae and mouthparts. Compound eye. In most insects there is one pair of large, prominent compound eyes. It is composed of several units called ommatidia. There may be up to 30,000 ommatidia in a compound eye. This type of eye gives less resolution than the vertebrate eye, but it gives acute perception of movement -important in flight. Digestive system The digestive system is complete. The mouth is surrounded with jointed mouthparts that gather (possibly through piercing or biting) and manipulate food. The gut is usually divided into a foregut, midgut, and hindgut. Circulatory system The circulatory system is open; blood is pumped by a heart and circulates through the body cavity. Nervous system The nervous system is well developed, usually including eyes, antennae and other sensory structures. Reproductive system The male reproductive system consists of paired testes, each connected by vas deferens to a seminal vesicle, and then uniting to form an ejaculatory duct that enters a penis, which may have complex supporting structures associated with it. The female system consists of paired ovaries, each of which is connected by an oviduct to a vagina. A spermatheca is present. Accessory glands are present in both male and female systems. Life cycles Developmentally, arthropods proceed from an egg, through larval and/or nymphal stages, to the adult. Note: Arthropods are usually ectoparasites, and may require 1 or more hosts to complete their life cycle. Many species move freely from one host to another, but others become attached permanently. Some species complete the entire life cycle on the host, but others attach only to feed and mate. Diversity There are over 1,000,000 described species of arthropod; of course only a fraction are parasites. Probably the greatest morphological diversity occurs among the crustaceans. Some species look nearly identical to their free-living relatives except for some minor adaptations for attachment; others are barely recognizable as arthropods. The arthropoda and its ways can affect our health Nuisance flies, ants etc Phobia Spiders, cockroaches etc Biting, sucking Ants, bed bugs, Horse flies, mosquitoes, sand flies, fleas Venoms and allergies Wasps, ants, bees, spiders, ticks, dust mites Disease, infestation Head, body and pubic lice, mites (scabies), Myiasis Disease vectors Two vector methods: • Mechanical - myxomatosis, bacteria by cockroaches and flies • Biological - requiring hosts in which the disease proliferates e.g. Malaria (disease) in humans (host) carried by mosquito (vector) Class Insecta Order Diptera (true flies) The true flies are one of the most important and popular insect orders comprising more than 100,000 described living species. Minute to medium size, rarely large insects, usually with good flight abilities. Antennae variable, formed by two basal segments and multi-segmented (usually up to 20 flagellomeres) to one-segmented flagellum bearing sensory style or arista in the latter case. Mouthparts licking or biting . Pro- and metathoraces small, immovably fused with large mesothorax. A- Bitting flies Mosquitoes Mosquito (from the Spanish or Portuguese meaning little fly) is a common insect. Mosquitoes have mouthparts that are adapted for piercing the skin of plants and animals. There are about 3,500 species of mosquitoes found throughout the world. In some species of mosquito, the females feed on humans, and are therefore vectors for a number of infectious diseases affecting millions of people per year. While males typically feed on nectar and plant juices, do not bite and therefore they do not transmit disease. the female needs to obtain nutrients from a "blood meal" before she can produce eggs. Note: The mosquitoes of medical importance are divided into: A-Anopheline mosquitoes which contains the important genus Anopheles. B- Culicine mosquitoes which contain three important genera, Aedes, Culex, and Man- sonia. Morphology Identifying Features of the morphology • Eggs of some mosquitoes float on the water in rafts. • Larvae, often called wigglers, have a soft body, a hard head and a breathing tube, or siphon, at the tip of the abdomen. • Pupae are shaped like a comma, and are commonly called tumblers. • Adults have delicate legs, a long proboscis and one pair of transparent wings. The mosquitoes have two wings, but unlike other flies, their wings have scales. The mouthparts of female mosquitoes form a long piercing-sucking proboscis which can pierce skin and suck blood. Males differ from females by having feathery antennae and mouthparts not suitable for piercing skin. Female mosquitoes are usually larger than males. Females have

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