Insect 15 Slides - SUNY Geneseobosch/Insects.pdf · (black fly) (Japanese beetle) Less Familiar...

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Myriapods and

Insects CH 14

Subphylum Mandibulata (continued from Crustacea)

Myriopods: “myriad of legs”

Centipedes (Chilopoda) Millipedes

(Diplopoda)

Similar to insects in many ways: --Uniramous appendages, trachea, excretory system --Antenna, mandibles, 1st &2nd maxilla,

maxilliped as poison gland in centipedes --Two distinct body regions: head-trunk -- Millipedes and centipedes found in late Cambrian marine fauna; considered two independent invasions of land

More on Myriapods: All terrestrial, mostly nocturnal, relegated to moist conditions in forest, moist soils rotting logs The cuticle is not waxy and allows considerable water loss. Also, spiracles of tracheal system are unable to close during respiration Millipedes: herbivores; fused segments, 2 pr of leg per Centipedes: maxillipeds as fangs; night hunters

A. Introduction B. Basic characteristics

What distinguishes insects? C. Insect Reprod. & Early Development E. Metamorphosis F. Exoptergygota and Endopterygota G.  Hormonal Control of Metamorphosis H.  Insect Societies

Super Class Hexapoda (6 legged arthropods)

Class Entognatha Class Insecta

Protura Collembolla

Class Entognatha

(springtails)

- Wingless - Mouthparts within a special pouch on the head

- Without metamorphosis -  Branched off before the

evolution of insects

Diplura (questionable affinity)

(two-pronged bristletails)

Thysanura (silverfish)

Class Insecta

- Considered the most primitive true insects

-  Wingless -  Without metamorphosis

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Familiar Animals

Order Diptera (150,000 species)

Order Coleoptera (360,000 species)

Great diversity of Flying Insects (Pterygota)

(black fly) (Japanese beetle)

Less Familiar Organisms

Order Mallophaga (2500 species)

biting lice (secondarily wingless parasites)

Diversity

Order Lepidoptera (160,000 species)

Meets the Order Mantoidea (2,000 species)

Exotic animals Success of Insects - 35 to 40 orders, 0.75 - 1.5 million species 2-3 thousand described every year; outnumber all other animal species combined - # of individuals in most species is high

e.g. locust

- found in practically every major habitat (one exception is the deep sea) - great economic importance

…as pests ...Vectors of disease Female Anopholes

Benefits: •  as predators of other insects

(parasitoid dipterans, hymenopterans) •  as producers…honeybees, silkworms •  as pollinators of plants

Malaria, plague, typhoid and yellow fever…….

Mountain pine beetles

Reasons for Success

- High reproductive potential - example: termite queen lays 200,000 eggs/day - Small size: most insects 1-2.5 mm in length large numbers for any given food supply - Metamorphosis: larva or nymph and the adult

stage do not compete for food - Wings and Flight: gain in dispersal, escape predation, exploit resources

- Exoskeleton

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Class Insecta = Hexapoda Characteristics

Uniramous appendages

- Four cephalic appendages: antenna, mandibles 1st maxilla, labium (fused 2nd maxilla) - Most appendages are uniramous (but evolved from polyramous, possibly even biramous types)

Insect Body Plan

- 3 Tagma: Head, thorax, abdomen; thorax as 3 segments, pro, meso, metathorax

-  1 pair of legs per thoracic segment; wings in meso and metathorax (1 pair on each)

- Abdomen usually with 11 segments; repro. structures; - Compared to crustacea, Abdominal appendages have been lost

Respiratory system of spiracles and trachea

•  System of tubes that deliver oxygen directly to flight muscles and other cells!!

•  Air taken into spiracles (by action of abdominal muscles) into tracheal tubes then to tracheoles and finally to individual cells. •  Respiration is independent of blood circulation

Spiracle

Trachea Tracheoles

Muscle fibers

Hollow tubes between hemocoel, (where waste is collected) and the gut where waste is removed. Distally K Urate in dissolved form enters the tubule.

Highly alkaline Acidic

Excretory and osmoregulatory Malpighian tubules

As pH drops proximally, uric acid is formed, water and potassium is reabsorbed. Waste is in the form of a crystal, uric acid and water is thus conserved.

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Class Insecta = Hexapoda Reproduction • Insects are dioecious (separate sexes)

• Sperm transferred in a specialized container (spermatophore)

• Fertilized Eggs Require protection: oviposition in water

or in other insects or in plant tissues

- - After fertilization, nuclei duplicate and migrate to the perimeter of the embryo, , cellularize and form a blastula

Link to Video

Reproduction and Development

- Segments begin to develop in sequence resulting in formation of head, thorax and abdominal region

http://www.cals.ncsu.edu/course/ent425/tutorial/embryogenesis.html



Class Insecta = Hexapoda Types of Post-Embryonic Development (metamorphosis)

1. Ametabolous: no larva or nymph wingless primitive insects

such as springtails and collembolans Miniature adult; without any major change in form

Examples : bristletails silverfish

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2. Hemimetabolous

• Immature aquatic stage, or naiad; similar to the adult but the wings are not fully developed.

• Wing pads can be seen on advanced instars

• Common orders : Ephemeroptera (mayflies) Odonata (Dragon Flies, damsel flies), Plecoptera (stone flies)

mayfly Dragonfly naiad

Dragonfly emerging

3. Paurometabolous: similar to hemimetabolous

Usually involves terrestrial forms such as grasshopper. The immature stage is the nymph

4. Holometabolous -- Young is different from adult in nearly every respect. -- Called a larva; it must pupate

and undergo a profound metamorphosis to the adult stage or imago. -- The pupa in beetles is called a grub,

in flies a maggot, crysallis for butterflies

Why Imago? “Apparition” ?

larva pupa

mosquito

Imaginal Discs in Holometabolous Development

Imaginal discs have not been found in animals with incomplete metamorphosis



Class Insecta = Hexapoda

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Apterygotes Order Diplura (silverfish)

Exopterygotes Endopterygotes No longer used in Taxonomy as they were paraphyletic taxa



Class Insecta = Hexapoda

Insect hormonal control of metamorphosis -  PTTH produced by cells in the brain enters the corpora cardiaca (neurohemal organs associated with the aorta) - Increasing PTTH levels in the blood induce the Prothoracic gland to produce ecdysone

- Action of ecdysone is modified by juvenile hormone (JH) from the corpora allata; JH suppresses expression of “adult genes”

- What triggers cessation of JH production? Genetics.

JH in red Prothoracicotrophic hormone (PTTH)

Insect Social Systems --Truly Social Insects (Eusocial) include:

-- all ~9500 ant species -- honeybees, a few wasps Hymenoptera

-- termites

-- Colonies are made up of Castes in all 3 groups: bees: workers (all sterile females), queen, drones

Insect Social Systems --Truly Social Insects (Eusocial) include:

-- all ~9500 ant species -- honeybees, a few wasps Hymenoptera

-- termites

-- Colonies are made up of Castes: ants: workers, soldiers, queen, males queens control sex of offspring by pheromones

Waggle dance of the honeybee

Insect Social Systems

worker soldier Flying female

male

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Insect Social Systems Inclusive fitness: Haplodiploidy: Males are 1N, females 2N There is an asymmetrical degree of relationship

Mothers are 1/2 related to daughters Sisters are 3/4 related to each other

But termites, snapping shrimp also eusocial yet not haplodiploid so other adaptive values may exist

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Insect 15 Slides - SUNY Geneseobosch/Insects.pdf · (black fly) (Japanese beetle) Less Familiar...

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