Download ESPM 134 Insects 1 Introduction to the Insects: Diversity and

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