Entomology - Morphology and Physiology

What is an exoskeleton

The external hardened, cuticular skeleton to which muscles are attached internally

What does integument mean

tough, outer protective layer

What does the exoskeleton do

• Provides a barrier against desiccation

• provides structure and support

• surface for internal muscle attachment

• protection from damage and infection

• sensory interface with environment

What is the main challenge of having an exoskeleton

Growth

What is the structure of the exoskeleton (name the layers from the inside to the outside of the insect)

1. Basement membrane

2. Epidermis

3. Cuticle

   1. procuticle

   2. epicuticle

What is the function of the epicuticle

cement layer that protects from abrasion, and wax layer that creates a barrier to water movement (keeps water in)

What is the structure of the procuticle

chitin microfibers surrounded by matrix of protein

What is the structure of the epidermis

single-layer of secretory tissue

What does the epidermis do

produces cuticle layers (only living layer of the exoskeleton) using dermal glands

What is the function of the basement membrane

separates body cavity from integument

What is chitin

a nitrogen-containing polysaccharide

What makes up the polymer chitin and how are they grouped together

repeating units of monosaccharides to form chains, which are grouped into bundles that have strong hydrogen bonding

how are the bundles of monosaccharides put together

the bundles align parallel to form sheets

how are the sheets of polysaccharides in chitin arranged

they are deposited at different angles in a rotation to create a helical arrangement

What are the physical properties of chitin

pliable, resilient, and tough

What two layers can the procuticle be split into

The exocuticle (closer to epicuticle) and the endocuticle (closer to epidermis)

What is the exocuticle and it’s function

It is the sclerotized portion of the procuticle. It functions as a hard armor for the insect

What is sclerotization

this is the stiffening of the cuticle by cross-linkage of protein chains creating dark rigid plates

What is the advantage of unsclerotized membranes

it allows insects to move around and expand since it’s softer and more flexible

What is resilin

a rubber-like or elastic protein in some insect cuticle

What are two different types of cuticular extensions

Spines (multicellular) and Setae (single-cell and hair like)

What causes variation in the coloration of insect exoskeletons

both pigments (chemical) and structure (physical)

What is the Cyphochilius beetle known for, where is it native to

it’s known for being among the whitest insects in the world, due to it’s ability to reflect 99.6% of all light (chitin and air bubbles allow this). It’s native to Asia, and it has been important for product development because of it’s passive cooling abilities.

What is the Namib Desert darkling beetle known for, and how is it important for product development

The bumps on the insect attract water droplets that are maintained by it’s waxy exoskeleton. The insect can tip it’s backside up, allowing the water to gather around it’s mouth for drinking. This is important for product development because biotechnology has been able to mimic it in order to create a water reservoir for people living in the desert.

How do insects grow?

through molting

What is molting

a two-step process including the formation of new cuticle and shedding of old cuticle

Explain the first step of molting

The cuticle separates from the epidermis (apolysis), and the epidermal cells divide and secrete molting fluid into the apolysial space that is inactive at this point

Why is the molting fluid inactive in step 1 of molting

This is so that the enzymes in the molting fluid don’t digest any living cells

Explain step 2 of molting

Epidermal cells secrete new epicuticle and the enzymes in the molting fluid activate after the epicuticle is there to protect the epidermis from digestion

Explain step 3 of molting

The old endocuticle is digested and reabsorbed, and new, undifferentiated procuticle is formed

Explain step 4 of molting

The remnants of the old cuticle separate/open along the weak line (suture)

Explain step 5 of molting

The insect undergoes ecdysis, leaving the exuvium behind

What is ecdysis

escape from the old cuticle

what is the exuvium

the old cuticle remnant, includes the exocuticle and epicuticle

Explain step 6 of molting

The cells expand, new cuticle swells and expands as it is straightened out

Explain step 7 of molting

The procuticle differentiates in exocuticle and endocuticle, and then sclerotization of the exocuticle happens

What is a teneral adult

a newly molted insect before sclerotization

What is the function of PTTH (Prothoracicotropic hormone)

it starts the process of molting by activating the prothoracic glands to secrete ecdysone

What is ecdysone

it is the molting hormone, it initiates the growth and molting activities of the epidermis

What releases PTTH

Corpora cardiaca

What do the prothoracic glands do

they produce ecdysone after stimulated by PTTH

What is metamorphosis

The relatively abrupt change in body form and physiology between the immature and adult stages

What does hemimetabolous mean

incomplete metamorphosis - development in which the body form gradually changes at each molt

What does holometabolous mean

complete metamorphosis - development in which the body form abruptly changes at the pupal molt

What is determinate growth

means that there is a certain number of molts and the growth ends at the adult stage

immature hemimetabolous insects are called what

nymphs

How do the wings of hemimetabolous insects develop

externally (exopterygote)

immature holometabolous insects are called what

larvae

how do the wings of holometabolous insects develop

internally (endopterygote)

How do hemimetabolous insects differ from holometabolous insects

• holo immatures are larvae and don’t resemble adults while hemi immatures are nymphs and resemble adults

• holo wings develop internally while hemi wings develop externally

• holo larvae and adults have different ecology while hemi nymphs and adults have similar ecology

how are hemimetabolous and holometabolous insects similar

both have determinate growth

Why is it a key innovation for larvae and adults to have different ecologies

this is because it led to an increase in diversity

T/F: All arthropods molt

false

T/F: All arthropods undergo metamorphosis

false

T/F: insects continue to molt as adults

False

What does ametabolous mean

means no metamorphosis, no change in body form during development, indeterminate growth

What is indeterminate growth

there’s no determinate number of molts, they continue molting even in adulthood (no terminal adult)

Which hexapods are ametabolous

non-insect hexapods and apterygote insects

What does juvenile hormone do

determines the body form/outcome of the molt by inhibiting development of adult characteristics before the final molt (suppressing hormone)

What produces juvenile hormone

corpora allata

For a particular pupating organism that normally has five instars, what would happen if the corpora allata was removed at the fourth instar

The insect would become an adult sooner, so it have a smaller pupa, and be a smaller adult

What would be the affect of inserting the corpora allata from a young larva into a 5th instar (last instar before pupation)

There would be an additional larval molt, causing the pupa and the resulting adult to be giant

draw out diagrams for hormones and hemi/holometabolous

What are IGRs

insect growth regulators - chemicals that disrupt normal insect growth and development

What are juvenile hormone mimics

IGRs that keep an insect from reaching adulthood

What are ecdysone receptor agonists (mimic)

IGRs that induce premature molts

What are chitin synthesis inhibitors

IGRs that inhibit cuticle formation

What are the applications of IGRs

they are useful in agriculture, horticulture, forestry, livestock, and households

What are the advantages of IGRs

• specific to insects

• harder for insects to evolve resistance to

What are disadvantages of IGRs

• timing - they are only effective when immature insects are exposed

• relatively slow process

What is example of a naturally occurring IGR

• some plants produce an ecdysone mimic when they are fed on, causing the insect to molt prematurely and die

• a specific example is in lettuce roots. Root herbivory by fungus gnats increases PE (ecdysone mimic) concentration in lettuce roots. The PE causes the gnats to die sooner and pupate too early

What are the three tagmata of insects specialized for

• Head - sensory and ingestive

• Thorax - locomotor

• Abdomen - digestive and reproductive

Explain the evolution of insect tagmosis

• a segmented, worm-like ancestor had 20 body segments

• development of paired appendages on each segment happened

• anterior (head end) segments begin to differentiate

• 6 segments (P +1-5) consolidated into a compound head, and the appendages form mouthparts and antennae

• 3 segments (6-8) become the thorax, and the appendages develop into jointed les for locomotion

• the remaining 11 segments become the abdomen, and the segmented appendages disappear (except segments 8,9, and 11 of the abdominal region)

What is the function of antennae

smell

What is the function of compound eyes

vision

what are ocelli and their function

they are light-sensitive “simple” eyes that only help to sense light and dark

What is the sensory equipment located on the head (excluding mouthparts)

• antennae

• compound eyes

• ocelli

What are the mouthparts on the head

• labrum

• mandibles

• maxillae

• labium

• palps

What is the labrum

upper lip

what are the mandibles

jaws, that cut and macerate (soften) food

What are the maxillae

accessory jaws that assist mandibles in processing food

what is the labium

lower lip

what are palps

sensory organs to sample food before ingestion

Recognize what all the organs on the head look like