Entomology Exam 2 topics

Hemolymph

Insect’s medium to transport substances to and way from cells in body (blood, except its for open cavity bodies rather than “closed” like other animals)

Functions of hemolymph

1. Lubricant for tissues - allows movement for organs

2. Hydraulic medium for hydrostatic pressure

3. Transport medium for many molecules, including wastes (not for oxygen, though)

4. Storage (Amino acids, sugars, H2O)

5. Protection (ex) immune response)

Osmeteria

Uses hemolymph as a hydraulic medium for hydrostatic pressure; “horns” (in caterpillars) that inflate with hemolymph using hydrostatic pressure when threatened by predators.

Ptilinum

• (In fly pupae) formed for partial development, but the fly stays in for some safety

• During development, the fly must eventually break out of this (last) larvae exoskeleton before finishing its metamorphosis.

• Breaks out using hydrostatic pressure (via hemolymph as “hydraulic medium”) and a combination of flexible, nondeveloped parts (legs) and sclerotized, hardened parts

• After escaping, the nondeveloped parts finish sclerotizing.

Reflex bleeding

• External bleeding to repel predators since they’d think that the trickster is too “sick” to be eaten

• Aligns with protection function of hemolymph

• Ladybird beetles do this

(Insect) Heart

• “Pump” present in open circulatory system

• A dorsal tube with holes undergoing peristalsis

Peristalsis

• Present in insect heart; defined as the progression of coordinated contractions of involuntary circular muscles

(Insect) Aorta

Tube (shorter than heart) lacking holes. Ventral in insect, in front of the heart.

Accessory pulsatile organs

Muscular structures helping hemolymph flow to extremities like wing veins (fast enough circulation to keep wing alive). An example of their location would be next to the wings’ base.

Functions of hemocytes examples

• Phagocytosis

• Encapsulation

• Hemolymph coagulation

• Storage and distribution of nutrients

Encapsulation is used when…

Parasitic wasps plant their eggs in other insects (ex) Drosophila), aka when invading organisms are too large for phagocytosis.

Steps of Encapsulation

1. Once the invader is recognized inside the insect, granulocytes release aggregation factors into the invader, attracting plasmatocytes to the area.

2. Plasmatocytes flatten out and cover the surface, forming 50+ layers of cells. This coats the invader, marking it as the basement membrane of the integument. The invader is now a capsule.

3. The capsule is covered with glycosaminoglycans: similar in composition to basement membrane.

4. Some plasmatocytes contain phenoloxidases → capsule becomes melanized + sclerotized, killing the invader inside of it → the killed invader now appears as a dark spot for the former host’s entire life.

Tracheal system

• A system of internal tubes where gas exchange in insects occur

• Oxygen is carried directly to areas where it is used - in most cases, hemolymph is not involved in oxygen transport due to this.

• Made up of the trachea, tracheoles, spiracles, taenidia, and intima

Trachea

• Formed by invagination of ectodermal tissue and are lined with a cuticular intima of the cuticle

  • Arranged in taenidia

  • Branch into finer tubes (tracheoles)

Tracheoles

• Branches of trachea (part of tracheal system)

Where are there a disproportionate amount of tracheoles in an insect’s body?

There are a disproportionately high amount of tracheoles in the thorax: much oxygen is needed for flight; the brain also needs lots of oxygen, so many tracheoles are in the head as well.

Taenidia

The product of the intima that wraps around the trachea (tube) in spiral folds. Its size is proportional to the diameter of the tube.

Intima (of tracheal system)

Endocuticle and epicuticle substances that line the trachea. Its arrangement forms spiral folds that are known as the taenidia.

Diffusion in insects are…

Sufficient for small enough insects, but larger insects supplement diffusion with abdominal pumping/ventilation.

Ventilation

The contraction and expansion of the volume of tracheal tubes done by abdominal pumping. In larger insects, this process, when combined with diffusion (along a concentration gradient), carries inhaled oxygen throughout the entire tracheal system.

Abdominal pumping

Muscular contractions that change shape of the abdomen, assisting in the ventilation (respiratory) process.

Spiracles

Holes on the integument (small enough to retain water) that take in oxygen for respiration

What are air sacs?

Air sacs are tracheal regions in many insects that have dilations and decreased taenidia. They are therefore easily compressed by changes in hemolymph pressure

Air sacs’ use in flight insects

Their ability to be compressed automatically by flight muscles makes them able to better deliver more, adequate oxygen to active flight muscles (useful for flying)

Problem of flight muscles and oxygen; what is the solution?

In flight, flight muscles’ oxygen demands exceed more than other tissues. However, other tissues, the CNS especially, cannot be derived of oxygen. The solution is the use of isolated air supply/degenerate trachea.

Isolated air supply in Schistocerca

To protect CNS’s oxygen supply, the head’s oxygen supply is given by spiracle 1. The degenerate trachea to the thorax prevents massive drainage of anterior air supply during flight

Degenerate trachea

Collapsed trachea that decreases oxygen transfer in tracheal tubes between the flight muscles and head

• “Head directed air” doesn’t reach flight muscles, and vice versa

• Ability to regulate isolated air supply/degenerate trachea by opening/closing spiracles

What is the greatest physiological challenge for aquatic insects?

Getting oxygen

How are most aquatic insects like?

They live at the water’s surface, and have no specialized structures/behaviours for obtaining oxygen; air is exchanged with the tracheal system via spiracles (like terrestorial insects)

Aquatic insects that submerge themselves either part of the time or all the time have…

special adaptations that allow them to obtain oxygen

Respiratory siphon

• Like a snorkel

• Submerged aquatic insects can access atmospheric oxygen directly through these

• Can be 6x as long as body (rat-tailed maggot) to reach surface

• Thoracic spiracles are posterior; this structure is aka the spiracle

• No reliance on water for gas exchange

• Usually have water repellent hairs around opening:

  • Underwater, they close up and prevent water from entering structure

  • Above water, they spread out and push water away from opening

• Can be used to indirectly acquire atmospheric oxygen: some mosquito larvae pierce into aquatic plants’ tissues that are filled with air

Cutaneous ventilation in aquatic insects

Very small insects with a thin cuticle can absorb dissolved oxygen directly from water, even if they have other modified structures for oxygen uptake

What are the two types of physical gills?

Compressible gill and plastron sensilla

Tracheal gills

Thin, feathery or leaf-like structures with abundant trachea

• closed trachea system (no spiracles, high surface area)

• ex) odonata naiad, ephemeroptera naiad

Compressible gills

• “scuba tank” carried by posterior of abdomen

• bubble of air that extracts oxygen from surrounding water

• insects trap a bubble of air in contact of spiracles pointed upwards

• bubble has gas concentration equal to that of atmosphere: less oxygen than N

• well concentrated water has more oxygen than bubble: oxygen diffuses from water into bubble, replenishing oxygen used by insect

• CO2 diffuses out of bubble into water

• water has less N than bubble, so N, which maintains bubble’s shape, diffuses into water - causing the “time limit” as bubble shrinks to a useless size

Plastron sensilla

• thin layer of air held close to body surface by tiny, densely packed water repellent hairs

• air bubble does not shrink (hairs, not N, maintain shape of bubble)

• insects with these structures can theoretically stay underwater for entire life (no time limit)

• this structure is used by eggs and immobile insect stages