Entomology Exam 2

What are the three tagmata

Head, thorax, abdomen

Important constituents of head tagmata

sclerotized capsule used for sensation, eating, and information processing

Important constituents of thorax tagmata

3 ancestral segments each bearing 1 pair of legs, segments 2+3 with wings, used for locomotion

Important constituents of abdomen tagmata

multiple segment, contains digestive tracts, genitalia (reproduction), and air sacs for respiration; some larvae / nymphs also use it for locomotion; digestion, reproduction, respiration

What are the layers of integument

cuticle, epidermis, and basement membrane

Cuticle purpose & components

non-cellular layer “exoskeleton” provides most of the structural main functions of integument

Epidermis purpose & components

one-cell-thick layer of living cells, secretes cuticle and performs glandular and sensory functions of integument

Basement membrane purpose & componentss

non-cellular layer (like chicken egg membrane), provides scaffolding for epidermis

tagmosis

the fusion of segments into functional units

tagma (pl. tagmata)

the distinct functional body regions formed by the fusion and differentiation of segments

Cephalization

creating the head from a fusion of 6 ancestral segments into a single, highly sclerotized capsule

Sclerotization (tanning)

the process by which an insect's or arachnid's exoskeleton hardens and darken (crosslinking various proteins called sclerotins)

Sclerite

a component section of an exoskeleton

Sclerotins

the proteins reinforcing exoskeletons through crosslinkage (stiffens chitin)

Cerci

a pair of appendages found at the end of an insect's abdomen that primarily function as sensory organs (helping the insect detect air currents, vibrations, and potential predators)

Tergite (tergum, pl. = terga) vs. sternite (sternum, pl. = sterna)

sclerites on the dorsal vs. ventral abdomen

Pleural membrane

soft part of the cuticle that joins tergites and sternites laterally (enables abdomen expansion)

Integument meaning

outer covering of the body

Main sections of insect integument

cuticle (exoskeleton), epidermis, basement membrane

Functions performed by the insect integument

Skeletal support, Locomotion, Water conservation, Sensory capabilities, Defense and offense,Exocrine glands, Respiration, Digestion

Layers of the cuticle

Epicuticle (outermost), exocuticle, endocuticle

What is Epicuticle made out of and what does it do

lipoproteins, waxes, oils; like “paint job” of cars and does not provide structural support but rather chemical interfacing with outside world (including water retention)

What is Exocuticle made out of and what does it do

cross-linked (sclerotized) chitin and proteins, is rigid and hard to provide structural support, also most responsible for color

What is Endocuticle made out of and what does it do

non-cross-linked chitin and proteins, is strong and flexible but not rigid or hard

How does color work in insects

mostly structural (light reflected/refracted) based on structure of chitin matrix (NOT chemicals like dyes)

How is chitin used in insect integument

forms the structural foundation, providing rigid exoskeleton that offers protection, support, and acts as a barrier against water loss

steps of ecdysis

0. Proliferation of epidermal cells

1. Apolysis: separation of old cuticle from epidermis

2. Secretion of inactive molting gel by epidermis

3. Production of epicuticle layer for new cuticle

4. Activation of molting fluid

5. Digestion and absorption of old endocuticle; epidermis

6. secretes new procuticle

7. Ecdysis: shedding the old exocuticle and epicuticle

8. Expansion of new integument

9. Sclerotization of new exocuticle

what is chitin

amino polysacchiride similar to cellulose arranged in microfibrils sheets (lamellae) layered out of alignment for more tensile strength; made rigid and hard (also brittle and unrecoverable chemically) by sclerotization (also usually darkens cuticle)

Limitations of a chitinous cuticle

size constraints (tubular structures aka insect limbs/body cavities are strongest at small diameter), cannot grow continuously (must molt)

chitin lamellae

sheets of microfibrils

chitin microfibril

bundles of H-bonded chitin embedded in a protein matrix

scaling laws (of physics)

Commonly encountered forces (such as adhesion, air resistance, kinetic energy) acts on insects differently from how we experience the forces because some forces scale linearly, others with the square, and others with the cube of one’s body length

how are physics “different” for insects

adhesion is strong for insects, kinetic energy is weak for insects, air is “gooey”

synchronous muscles

1 neural signal = 1 contraction, in all animals

asynchronous muscles

1 neural signal = many contractions, generates extremely fast wingbeats, only in insects

why can insect legs move faster than human legs in terms of number of steps per unit time

forces scale differently with muscle strength and cross sectional area relative to mass/inertia of each leg

myosin and actin

cause contraction of muscle fibers

apodemes

internal ridges/ingrowths of the integument that serve as attachment points for muscles

prolegs

non-jointed appendages on the abdomen of some insect larvae used for gripping and locomotion

Resilin

a rubber-like protein in insects that acts as a molecular spring

Metafemoral spring

triangular plate

elastic plate

direct vs. indirect flight

muscles attached to wings vs. muscles distorting thorax to move wings

pros and cons for direct flight

pros and cons for indirect flight

the only orders who use direct flight (hint: Paleoptera orders)

Odonata, Ephemeroptera (mayflies)

evidence for flight being a costly investment

secondarily wingless insects; alates in insects that have both winged and wingless forms

examples of how wings are used for purposes other than flight

Ruan et al. 2020: what question did they set out to solve?

How do flea beetles achieve impressive jumps? (previous research disagrees)

Ruan et al. 2020: What was their experimental approach?

Micro-CT scanning analysis of 7 species to build 3D models of internal structure, 13 genera dissected, high speed filming of 4 species

Ruan et al. 2020: What did they find out about how flea beetles jump (what body parts are involved to generate and release the necessary forces)?

Tibial extensors stretch metafemoral spring to store elastic force, tibial flexor keeps tibia folded with help of triangular and elastic plate acting as latch/protection mechanism

Ruan et al. 2020: What were the implications of their study?

information can be compared with other groups that store kinetic energy for rapid movement OR can be used to design robot based on beetle’s hind legs

How does the jumping mechanism studied in Ruan et al. 2020 work in principle? What parts are involved?

parts involved: the tibial flexor and tensor muscles, metafemoral spring, Lever’s triangular plate, elastic plate

Arolia

a pad-like organ on the underside of the insect "foot", formed by an extension of the last tarsal segment

pulvilli

how are insect legs used to stick to surfaces

arolia/pulvilli secrete fluids and/or bear tiny hairs to adhere to smooth surfaces, surface tension and adhesion forces hold on water, Van der Waals forces on walls