Insecta

- A very fast overview

Diversity of eukaryotes

• Size of organisms represents number of species.
• Insects comprise ca. ¾ of all animal species.

Crustacea

Acari

Chelicerata

External morphology of adult insects

• Hard exoskeleton made of chitin.
• Three main sections: head (with mouth parts, compound and simple eyes and 2 antennae), thorax (with legs and wings), abdomen.
• Six pairs of legs and two pairs of wings!
• Mouth parts are diagnostic for different insect orders.

} Head

} Thorax

}Abdomen

Mouth parts of insects

Cockroach

Honey bee

Butterfly

Mosquito

Labrum (g)

Mandible (r)

Maxillae (y)

Labium (b)

Labrum (g)

Mandible (r)

Maxillae (y)

Labium (b)

Insect compound eyes

• Individual component: Ommatidium.
• One eye of a dragonfly contains 28,000 ommatidia.
• Aside from compound eyes, also individual eyes can occur: Ocellum.

Insect legs

Beetle

Grasshopper

Louse

Honey bee

Mole cricket

Variations of insect legs

Insect digestive and excretory systems

• Digestive system (GREEN): Pharynx→ Esophagus→Proventriculus→Ventriculus (absorption)→Malphigian tubules (BLUE: excretion)→Ilium→Rectum (reabsorption of water)→Anus.

• Spiculae (openings) and tracheae (pipes) for gas exchange (BLUE).
• Dorsal heart, open circulatory system (RED).
• Ventral nerve cord (YELLOW).

→ Compare with vertebrates!

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Internal morphology

Insect development

• In order to grow, immature insects have to shed their inflexible exoskeleton. They have to molt.
• Molting is controlled by hormones:
• Ecdysone is triggering molt.
• Juvenile hormone is suppressing adult characteristics. If levels decrease, pupation into adults is triggered.
• Artificial juvenile hormone has been used as insecticide.

Three different forms of development

• Metamorphosis: change of form.
• Ametamorphosis: no metamorphosis; immatures resemble adults, except size → most primitive insects, e.g. springtails.
• Gradual metamorphosis: Immatures resemble adults, except certain features, e.g. wings, coloration; juveniles are called nymphs or naiads → e.g. grasshoppers, cockroaches, dragonflies → HEMIMETABOLIC
• Complete metamorphosis: Immatures do not resemble adults; juveniles are called larvae and pupae → e.g. butterflies, beetles, flies, bees, → HOLOMETABOLIC

Systematic entomology

• Because of the immense insect diversity, only those orders (groups) will be introduced, which have high relevance for forests and forestry.
• Important functions in forests performed by insects are: predation, herbivory (including timber!), decomposition, parasitism, pollination, seed dispersal.

Orders Collembola, Diplura +Thysanura

• Most ancient insect groups.
• Without wings.
• Ametamorphic.
• Mouth parts chewing.
• Among the most important arthropod decomposers in leaf litter and forest soils.

Order Phasmida: Walking sticks and leaf insects

• Two pairs of membranaceous wings, often reduced in walking sticks.
• Hemimetabolic.
• Chewing mouth parts, mostly feeding on leaves of trees.
• Mimesis: Shape and color resembling twigs and leaves as protection against predators.

Orthoptera: grasshoppers and crickets

• Last pair of legs mostly adapted for jumping.
• Chewing mouth parts: Caelifera (short antennae) herbivorous, Ensifera (long antenna) omnivorous.
• Hemimetabolic.
• Important pests in agriculture, less so in forestry.

Caelifera

Ensifera

Order Isoptera: Termites

• Social insects with three ‘castes’: reproductive (‘king’ +‘queen’), workers (males + females), soldiers.
• Mouthparts chewing.
• Two pairs of membranaceous wings.
• Hemimetabolic.

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Feeding ecology of termites

• Most serious pests of timber and wood products, but also important decomposers.
• They can digest cellulose, some with the help of protozoans and Archaea.
• Biomass in some rain forests is 2,000 kg/ha and more than 1,000 ind./m².

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Order Hemiptera, Suborder Heteroptera - True bugs

• Superficially resemble beetles, but have sucking mouthparts.
• Hemimetabolic.
• Four membranaceous wings, first pair with thickened base.
• Feeding on plant sap, some can transmit plant diseases. Some groups are predators, few are parasites.

Order Hemiptera, Suborder Homoptera - Cicadas, hoppers, aphids, etc.

• Sucking mouthparts.
• Hemimetabolic.
• Two pairs of wings fully membranaceous.
• Many important pest species, feeding on plant saps. Some can transmit plant diseases.
• Aphids can build up populations very fast through parthenogenesis.

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Order Thysanoptera - Thrips

• Small insects (ca. 3 mm) with two pairs of fringed wings or wingless.
• Rasping/sucking mouthparts.
• Hemimetabolic.
• Some pest species, possibly most important pollinators of Dipterocarpaceae.

Order Coleoptera - Beetles

• Most diverse insect order with ca. 350,000 described species.
• Two pairs of wings, first pair as hard elytrae.
• Holometabolic.
• Chewing mouthparts.
• Occupy virtually all kinds of niches as predators, herbivores, decomposers or pollinators.

Wood beetles

• Many beetle families contain species which are important pests in forests and plantations.

Buprestidae

Cerambycidae

Curculionidae

Lucanidae

Scarabeidae

Order Hymenoptera – Bees, wasps, ants

• Social and solitary insects, second most diverse group after beetles.
• Chewing/lapping mouthparts.
• Holometabolic.
• Two pairs of membranaceous wings, coupled by hamuli.
• Some are very important pollinators, predators and even seed dispersers.

Hymenopteran states

• Some bees, ants and wasps have evolved the most complex social structures among invertebrates.
• ‘Castes’ are one reproductive females (‘queen’, mostly long-lived), repr. Males (mostly short-lived) and sterile workers.

Bees as pollinators

Bees in Borneo

• Social bees are more diverse than solitary ones.
• They are most likely the most important animals pollinators in Borneo’s forests: in Sarawak 32% of 270 plant species were pollinated by social bees, additional 18% by solitary bees.

Ants in Borneo

• Ants are by far the most ‘influential’ animal group in Borneo’s forests.
• In Sabah 524 species have been found in six ha of lowland forest.
• Some species are important predators → army ants.
• Some are seed dispersers; they can create specific associations of epiphytes → ‘ant gardens’.
• Some are associated with certain plants (Myrmecodia, Macaranga) in which they build their nests and which they provide with nutrients and defend against herbivores.

Lepidoptera – Butterflies and moths

• Conspicuous and well-known order.
• Sucking mouthparts.
• Holometabolic.
• Two pairs of wings, usually covered in scales and connected to form one functional pair of wings.

Butterflies and forestry

• Adult Lepidoptera mostly feed on nectar and some are important pollinators.
• Lepidoptera larvae (caterpillars) can be serious defoliating pests.
• Some larvae are destroying timber because of their wood-boring habits.

Trogonoptera brookiana

Examples for protective coloration

Mimesis

Mimicry

Diptera - Flies

• One pair of developed wings; second pair reduced to halteres.
• Sucking mouthparts.
• Holometabolic.
• Form of antennae diagnostic within the order Diptera: Nematocera with long, slender a.; Brachycera with short a.
• Some are pollinators; some are predators. Important pest species, e.g. of fruit trees.
• Some species are important parasites of humans and animals.

Malaria - Plasmodium

Human

Sporozoites in liver

After days, spor. are transformed into merozoites which infect repeatedly red blood cells. Typically fever every 48 or 72 hours.

Merozoites transform into Gamontes which can infect bloodsucking mosquitoes.

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Anopheles sp.

In the mosquito sexual propagation of Plasmodium takes place.

In the oocyte (‘egg’) thousands of sporozoites develop.

Mosquito

Mosquito bites human.

Syrphidae – wasp mimicry