Entomology File

Definition and Characteristics of Insects

  • An insect is an invertebrate classified under the class Insecta in the phylum Arthropoda.

    • Distinguishing characteristics include:

      • Segmented bodies with paired, many-jointed legs.

      • Three major body sections: head, thorax, and abdomen.

      • Six legs (three pairs).

      • Two antennae.

    • The term "insect" comes from the Latin word "insectum", meaning "cut up".

    • "Entomology" derives from the Greek word "entomos", meaning "cut in pieces", referencing the insect's tri-part body structure.

    • "Hexapod" refers to the six legs, and "arthropod" refers to jointed legs.

      • Both terms are derived from Greek origins.

    • Insects are the only arthropods capable of flight; however, not all insects possess wings. Some, such as Zygentoma and Archaeognatha, never evolved wings, while others have lost wings over time.

Insect Taxonomy

  • All insects are classified in the following hierarchy:

    • Kingdom: Animalia

    • Phylum: Arthropoda

    • Subphylum: Hexapoda

      • Includes classes and orders like Collembola, Protura, and Diplura. There's debate on if these orders belong to class Entognata or if they are separate classes.

    • Class: Insecta

      • Contains diverse orders of insects.

    • The 2025 Entomology List also includes the family Ixodidae (hardbacked ticks), which belongs to the order Ixodida within the subclass Acari (mites and ticks), classified under the class Arachnida in the subphylum Chelicerata.

Characteristics of Members of Taxonomic Groups

  • Kingdom Animalia

    • Features:

      • Heterotrophic,

      • Eukaryotic,

      • Multicellular,

      • No cell wall or chloroplasts,

      • Motile,

      • Have sense organs.

  • Phylum Arthropoda

    • Features:

      • Chitinous exoskeleton,

      • Must molt during growth,

      • Jointed paired appendages,

      • Segmented bodies divided into regions called tagmata (head, thorax, abdomen),

      • Bilateral symmetry,

      • Ventral nervous system,

      • Open, dorsal circulatory system.

  • Clade Mandibulata

    • Characteristics include modified appendages (mandibles) used as jaws.

Subphylum Hexapoda

  • Three pairs of legs located on the thorax, segmented into head, thorax, and abdomen.

  • One pair of antennae on head.

  • Many species have one or two pairs of wings.

  • Compound and simple eyes common.

Insect Identification Tips

  • Color is generally not a good identification marker.

  • Wing venation is crucial for identifying orders like Hymenoptera, Diptera, and Lepidoptera.

  • Learn defining traits of major orders:

    • Diptera: One pair of functional wings, the second pair modified into halteres.

    • Hymenoptera: Forewings usually larger than hind wings, connected by hamuli.

    • Coleoptera: Forewings modified into elytra for protection.

    • Lepidoptera: Two large pairs of wings, with connections (frenulum).

Insect Development

  • Morphogenesis: All changes to insects that involve growth, molting, and maturation.

  • Molting Process:

    • Triggered by hormones when growth reaches exoskeleton limits.

    • Each molt marks the transition from one instar (developmental stage) to another.

      • Process:

        1. Apolysis: Separation of old exoskeleton from the epidermis.

        2. Secretions of inactive molting fluid by epidermis.

        3. Construction of new cuticular layer.

        4. Activation of molting fluid.

        5. Digestion and absorption of the old endocuticle.

        6. Secretion of new procuticle by epidermis.

        7. Ecdysis: Shedding of the old exoskeleton.

        8. Expansion of new integument.

        9. Tanning (sclerotization) of the new exocuticle.

  • Types of Metamorphosis:

    • Ametabola: No metamorphosis; young resemble adults but are smaller; undergo molts to grow.

      • Examples: Protura, Diplura, Collembola, Archaeognatha, Zygentoma.

    • Hemimetabola: Incomplete metamorphosis with egg, nymph, and adult stages.

      • Examples: Ephemeroptera, Odonata, Blattodea, and others.

    • Holometabola: Complete metamorphosis with egg, larva, pupa, and adult stages.

      • Examples: Megaloptera, Neuroptera, Coleoptera, and more.

Larvae and Pupa Types

  • Larvic Types:

    • Eruciform: Generally cylindrical, like caterpillars.

    • Campodeiform: Flattened body, adapted for running.

    • Scarabaeiform: C-shaped, robust body, common in grubs.

  • Pupa Types:

    • Obtect (like a chrysalis): Developing appendages bound against the body.

    • Exarate: Appendages free and visible externally.

    • Coarctate: Encased in the last larval exoskeleton.

Insect Behavior

  • Understanding insect behavior, including communication and social structures is essential.

  • Social Insects: E.g., termites and bees show various forms of social behavior and interactions.

    • Various classifications (solitary to eusocial) are common based on nesting behavior, cooperative brood care, reproductive castes, and generation overlap.

  • Advantages of Social Living:

    • Construction of large nests.

    • Efficient foraging and constant vigilance against threats.

  • Disadvantages of Social Living:

    • Disease spread in colonies.

    • Competition for resources.

Insect Ecology

  • Understand trophic levels of insects: consumers in all levels of the food chain except the primary producer stage.

  • Insect Feeding Groups:

    • Herbivores: Phytophagous, can be monophagous, oligophagous, or polyphagous.

    • Carnivores: Zoophagous insects that consume other animals; usually predatory.

    • Parasitism: Organisms (parasites) that exploit a host, potentially harming them.

      • Include endoparasites (inside) and ectoparasites (on the surface).

    • Decomposers: SAPROPHAGOUS insects critical in recycling nutrients and breaking down organic materials.

  • Insects impact human life as both beneficial (pollinators, decomposers) and harmful (agricultural pests, disease vectors).