insect physiology

Vitrification Hypothesis

Hypothesis for how cells survive dehydration:

• Cell contents form a glass-like state

• Molecular movement stops

• Cellular structures are stabilized

 Water Replacement Hypothesis

Hypothesis for how cells survive dehydration:

• Molecules (mainly trehalose) replace water

• Maintains structure of:

  • membranes

  • proteins

  • macromolecules

Cryptobias

an extreme dormant state where organisms appear almost dead but can revive when conditions improve.

Characteristics:

• Metabolism becomes nearly undetectable

• Organisms survive otherwise unsurvivable conditions

Pros of Dormancy

• avoidance of inclement conditions

• synchronizing (food source/same species)

difference between diapause & quiesence

diapause is programed, quiescence is not.

In addition, quiesence starts after conditions become unfavorable & ends when conditions improve.

In temperate insects, diapause is cued by..

changes in the photoperiod

Stage specific diapause

some examples

• Egg: Asian tiger mosquito

• Larvae: pitcher plant mosquito / eurytoma gigantea

• Pupae: flesh fly / eurytoma obtusiventris

• Adult: house mosquito / paper wasps

Types of Diapause

Facultative Diapause

• Occurs only under certain environmental cues

• Common in temperate insects.

Obligate Diapause

• Happens every generation

• Required for development.

Phases of Diapause

Induction → Preparation & Entry → Maintenance → Termination → Post-diapause Quiescence

What two forces control ion movement across membranes?

→ Chemical force (diffusion)
→ Electrical force (voltage)

Why is the inside of a neuron negative at rest?

K⁺ leaks out of the cell, leaving excess negative charge inside.

What is chemical force?

Movement of ions down their concentration gradient

What is electrical force?

Movement of ions due to membrane potential

E_ion < V_a

Electrical force dominates & drives Na+ out of the cell

E_ion > V_a

Chemical force dominates & drives Na+ into the cell, even against a positive chemical force

What is a graded potential?

A voltage change that decreases with distance

What is an action potential?

A rapid, all-or-none electrical signal that travels along the axon.

Why do some insect neurons not need action potentials?

due to how small insects are, some neurons are able to send signals w/only passive signal propigation

What channels generate action potentials?

Voltage-gated Na⁺ and K⁺ channels

What is light detected by?

Light is detected by rhodopsin, a G-protein coupled receptor (GPCR)

What is rhodopsin made of?

Opsin (protein)

Retinal (chromophore derived from vitamin A).

Key Themes Insect Vision:

1. Insect compound eyes are made of thousands of ommatidia.

2. Visual acuity is low but varies across the eye.

3. Light detection uses rhodopsin GPCR phototransduction.

4. Most insects have trichromatic color vision (UV, blue, green).

5. Many insects detect polarized light for navigation and finding water.

What is the basic visual unit of an insect compound eye?

Ommatidium (one of the MANY light detecting units which compose a compound eye)

What are the main parts of an ommatidium?

→ Corneal lens
→ Crystalline cone
→ Photoreceptor cells
→ Rhabdom
→ Screening pigment cells

What determines spatial resolution in compound eyes?

Interommatidial angle

What does a smaller interommatidial angle between adjacent ommatida yield?

Higher visual acuity

What is an acute zone?

A region of the eye with denser ommatidia and higher visual acuity

What type of receptor is opsin?

G-protein coupled receptor (GPCR)

What structural change occurs when rhodopsin absorbs light?

Retinal changes from 11-cis to all-trans

What type of signaling pathway is activated after rhodopsin changes shape?

Second messenger cascade

What ion channel ultimately opens during phototransduction?

TRP channel

What happens when the TRP channel opens?

Cations enter the cell, leading to depolarization

What are the three main photoreceptor types in most insects?

Blue, Green & UV

What is an ‘e-vector’?

A plane in which lightwaves vibrate

What natural source produces polarized skylight patterns?

The atmospheric scattering of light

About how many ommatidia are in the DRA?

~ 60

Which specialized eye region detects polarized light?

The Dorsal Rim Area (DRA)

Name the types of Insect Mechanosensors

Mechanosensory hairs, capaniform sensilla, & tympanic ears

What’s up with mechanosensory hairs?

These hairs ben when stimulated by touch/air movements, which activates a sensory neuron at the base of the hair

Elaborate on the role of campaniform sensilla

These are dome shaped sensor in the cuticle which detect strain and deformation in the cuticle. They help insects sense the forces acting on them

Tympanic Ears

Thin cuticle, sense sound pressure waves and vibrations caused by sound

Information from sensory hairs is integrated to the neuron system and directed to…

fourteen giant interneruoms

What are the characteristics of the Giant Internuerons?

• receive input from many sensory hairs

• located in the terminal abdominal ganglion

• have large axons

• rapidly transmit information to the thorax.

What triggers the ‘escape behavior’ response in cockroaches?

Wind detected by cercal hairs → sends signal to giant interneurons → GI’s transmit signals to cockroach legs → triggers 180º movement from source detection

What are EPSP’s?

excitatory post synaptic potentials

What are the characteristics of EPSP’s? What response can EPSP’s trigger?

• weighted (based on distance/length constant)

• summed across dendrites

• If total excitation exceeds threshold → action potential fires

How does ‘Descending Inhibition’ apply to insect neural activity?

Inhibitory signals from a higher neural center (e.g., the brain) suppress neural activity in some circuit

The brain sends signals down the ventral nerve cord which can suppress certain behaviours. (eg, male mantis s ex)