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ESPM 134 Insects 1 Introduction to the Insects: Diversity and Adaptations Why insects? Tremendous richness of species (1 million) and diversity of life styles Broad range of ecosystem services in forest environments Arthropoda Most successful phylum of animals (or organisms?) Characterized by chitinous exoskeleton, segmented bodies, jointed appendages Chelicerata - two body regions (cephalothorax and abdomen), no antennae, (spiders, horseshoe crabs, sea spiders) Myriapoda - many legs (1-2 per body segment), specialized defensive odors (centipedes, millipedes) Crustacea - mainly aquatic, two body regions (cephalothorax and abdomen), antennae, (barnacles, lobsters, shrimps, water fleas, copepods) Hexapoda Hexapoda Superclass of all 6 legged arthropods with three distinct body regions (head, thorax, abdomen) Protura – small (<2mm), delicate, unpigmented, lack wings and antennae, leaf litter Collembola (springtails) – small (<10mm), soft bodied, wingless, leaf litter Diplura – small (2-5mm),unpigmented, wingless, leaf litter Insecta Insecta Class of true insects, compound eyes, ectognathous (exposed mouthparts), tracheal gas exchange, genitalia on abdominal segments 8 (female) or 9 (male) Archaeognatha (bristletails) – larger, primitively wingless, occur in drier soil environments Thysanura (silverfish) – larger, primitively wingless, variety of habitats (also houses) Pterygota Pterygota Infraclass of winged insects, thorax of adult large usually with veined wings on 2nd and 3rd segments, metamorphosis Ephemeroptera (mayflies) – wings cannot fold, non functional adult mouthparts, aquatic scavengers or herbivores Odonata (dragonflies) – wings cannot fold, predators, aquatic predators Neoptera Neoptera Insects with wings that can fold back over the abdomen at rest Many poorly resolved orders of insects (attached Fig.) all with partial metamorphosis Orthoptera (grasshoppers, etc) – hind legs enlarged for jumping, largely phytophagous Isoptera (termites – within Dictyoptera) – social insects, cellulose feeders, dead wood Paraneoptera (book lice, lice, thrips, bugs) – orders in which mouthparts are modified as beaks for sucking and piercing, incomplete metamorphosis (Hemiptera - aphids, scales, true bugs) Endopterygota Endopterygota Neopteran insects with complete metamorphosis (pupal stage) Coleoptera (beetles) – front wings thickened as rigid elytra, wood borers, terminal miners, cone borers, root borers Hymenoptera (bees, wasps, ants, sawflies) – abdomen often separated from thorax by narrow waist, pollinators, parasitoids, predators, defoliators Lepidoptera (moths, butterflies) – wings covered with scales, defoliators, terminal miners, cone borers Diptera (flies) – single pair of wings, cone borers, parasitoids, predators, detritivores Success of the insects Small size – 1-10mm, facilitates partitioning of resources Short generation time – 7/10days-1.5 years, promotes more rapid genetic change in response to environment Sensory sophistication – required for controlled flight, allows fine scale interpretation of environment Trophic linkages – strong associations with other trophic levels, phytophagy, parasitism, coevolved radiations Metamorphosis – permits specialization for larval growth, and adult reproduction Flight – arose once (300 million years ago) from basal branches of legs, facilitates food specialization, escape, mate finding, dispersal Aspects of insect species richness Insects absent from marine environments, but often dominate terrestrial environments Succession – species richness influenced by both plant species richness and plant architecture (structural complexity) Latitude – species richness increases toward tropics, e.g. ants and bark beetles Distributional range – the larger the area occupied by a tree the greater the richness of insects (island biogeography – interplay between colonization and extinction) References Edmonds, Agee & Gara (2000) Forest Health and Protection - Chapter 18