Review Sheet -- Test 1 (Week 1)         Biology 4900 -- Entomology; James Adams

What is an Insect? See "Classification of Arthropods" handout
        Insects are in the Phylum Arthropoda (meaning "jointed appendages").

(Chapter 15, 16)
Distinguishing Characteristics of Arthropods:
    1. Jointed appendages (of course!)
    2. An exoskeleton (which must either be shed or added on to for growth)
            This exoskeleton provides protection, support and muscle attachment (like your endo-
            skeleton)
    3. Distinctly segmented body.

Several different subphyla are included in the arthropods (Know the bold faced groups)
        Trilobites (extinct)
        Chelicerates which includes Arachnids (spiders, scorpions, ticks, mites, chiggers, etc.)
        Crustaceans which includes crabs, lobsters, shrimp, isopods (pillbugs), etc.
        Myriapods, which includes centipedes (Chilopoda) and millipedes (Diplopoda)
        Hexapods -- this subphylum includes the insects and odd primitive orders

Some people believe Myriapods and Hexapods are sister groups, but more recently genetic
       studies strongly infer that hexapods are the sister to Crustaceans.  See my website and
       the link provided to a recent paper on the relationships of arthropods

Some important features of hexapods, shared with some other arthropod groups:
            See "Entomological Terms" handout
    1. Mouthparts that include:
        a. Labrum (upper "lip")
        b. Two pairs of food manipulating mouthparts: mandibles and maxillae
        c. Labium (lower "lip")
    2. One pair of antennae on head, which is freely moving from other segments
    3. Sclerites ("hard parts") on each segment: a top tergite, lateral pleurites, and a sternite
    4. Several internal structures:
        a. Respiratory system -- with tracheae and spiracles (usually two per segment)
        b. Digestive system -- with fore-, mid- (with peritrophic membrane) and hindgut
        c. Excretory system -- with Malpighian tubules
        d. Circulatory system -- open, with dorsal blood vessel carrying blood forward to head

Distinguishing Characteristics of Hexapods:
    1. Six legs, of course!
    2. Three body parts: head, thorax and abdomen
    3. Wings in many (but not all); any arthropod with wings is an insect

All Hexapods used to be called Insects (Class Insecta); you'll notice that your book mentions two 
    separate "groups" of hexapods -- the "Informal Group" Entognatha (containing the Protura,
    Collembola, and Diplura) and the Class Insecta . . . Why?

Because there are some distinctive differences between some of the most primitive hexapods and
    those that are considered true insects, though again, recent studies suggest that the Diplura
    are very closely related to insects and may belong with them. The Protura are very odd,
    with no eyes or antennae, and they even add segments as they molt the first four times.
    Springtails (Collembola) are also odd in their body segmentation (only 6 in the abdomen), and
    genetically appear to be the sister to the Proturans. Both Diplura and Collembola have fully
    musculated antennae (we'll explain this further). So there are some very strange primitive
    hexapods, but they are all considered hexapods (though not all are considered insects).

In this course, we will talk about ALL hexapods, but don't be surprised if I refer to all of them as
insects from time to time!

(Chapter 1)
Why study Insects, or Who Cares?!
    Insects are SUCCESSFUL, in many respects:
        1. They are diverse -- many, many different species in the world.
        2. They are numerous -- lots and lots of individuals.
        3. They have inhabited most parts of the surface of the earth, including being very diverse
            in the terrestrial (land) environment.

    Why have insects been so successful? (See pages 10 - 12)
        1. A multipurpose, largely water impermeable exoskelton, and internalized respiratory
            system.
        2. Inhabiting the terrestrial environment, particularly having done so before vertebrates
        3. A small body size -- minimal survival requirements
        4. A fast (short) generation time and tremendous production of immatures (young).
            Allows much more rapid evolutionary adaptation and ultimately speciation -- likely
                a major reason why insects are so diverse.
        5. Flight for the vast majority of species -- allows escape, finding resources and dispersal.
        6. Many have complete metamorphosis B reduces competition between life stages.

Still, why study insects? Because they influence YOU.
        1. Because they are so abundant, particularly in the terrestrial environment, you WILL
            encounter them.
        2. There are Beneficial insects -- Examples?
        3. There are Injurious insects -- Examples?

We will discuss the impacts of insects on humans in much greater detail later in the semester.