Introduce:
CHAPTER 4
INSECT PHYSIOLOGY
Insect physiology is the study of the structure and physiological function of the internal organs of insects, thereby understanding the relationship between structure and physiological function and between physiological activities and environmental factors. Understanding the impact of external factors on internal physiological activities is a necessary basis for proposing insect management measures in the direction that is most beneficial to humans and the environment.
Target:
Knowledge:
+ Provides knowledge about the structure, function and location of internal organs in insects.
Skill:
+ Understand the working mechanism of internal organs.
Ability to be self-reliant and responsible: have a spirit of learning, be proactive in learning, have a scientific and creative working method and always update information.
1. Muscular system of insects
The insect musculature is a complex system consisting of several hundred to several thousand muscle cells. Most are striated, even those surrounding the digestive tract and the heart. The musculature surrounding the digestive tract, heart, and oviduct produces peristaltic movements that help these organs function, such as helping the heart to contract, moving blood into the dorsal blood vessels, or moving food through the digestive tract and eggs or sperm through the reproductive tract. The musculature that moves appendages is usually arranged in segments, usually in symmetrical pairs. Usually each segment of each appendage has its own musculature.
Insect musculature is generally quite strong, many insects can push a weight 20 times their body weight and for some insects that can jump, insects can jump a distance many times the length of their body. Insect musculature can contract very quickly, expressed through the beat of the wings, beats of several hundred times per second are very common in insects, this shows that the musculature has a great impact on the physiological activities of insects.
2. The sinusoids and internal organs of the insect body
2.1 Sinusoidal body
The cavity inside the body formed by the insect's skin is called the corpus cavernosum. The corpus cavernosum contains the internal organs and has two thin partitions running along the body to form three small cavities: the dorsal hematoma, the intestinal hematoma, and the ventral hematoma. The partitions do not completely divide the corpus cavernosum, so the insect's body remains a unified whole.
2.2 Digestive system
Like other animals, insects use their digestive system to absorb nutrients and other materials from the food they consume. Most food in the form of large or complex molecules such as proteins, polysaccharides, fats, nucleic acids, etc. will be broken down into smaller units such as amino acids, simple sugars, etc. by catabolic reactions before being used by cells as a source of energy or materials for growth and reproduction. This metabolic process is called digestion.
All insects have a complete digestive system. In it, the process of digesting food occurs in a tube-like structure (called the alimentary canal) that extends from the mouth to the anus with specialized functional areas to undertake digestion, nutrient absorption and excretion. Food always moves through the digestive system in a single direction.
In most insects the digestive tract is divided into three functional regions: the foregut (stomodeum), the midgut (mesenteron) and the hindgut (proctodeum).
In addition to the digestive tract, the insect digestive system also has a pair of salivary glands and a salivary cavity located in the thorax next to the foregut. From the salivary glands, ducts run to the cavity across the head and into the mouth at the back of the pharynx. During chewing, the movement of the mouth helps mix saliva with food in the oral cavity.
a) Foregut
From the pharynx food passes through the esophagus, a tube connecting the pharynx to the crop, by peristalsis of the intestinal wall into the crop and remains there until it is passed through the rest of the digestive tract. Within the crop, some digestion may occur as a result of the action of enzymes in saliva, added as the food passes through the oral cavity, and enzymes secreted from the midgut.
In some insects, the crop opens posteriorly into a muscular stomach bearing minute tooth-like structures that help grind up food particles.
similar to the gizzard of birds. The foregut valve is a sphincter located just behind the muscular stomach that regulates the flow of food from the foregut into the midgut.
b) Midgut
The midgut begins just behind the foregut valve. Near the anterior border, the wall of the midgut has finger-like projections (usually 2–10) that provide additional surface area for absorption of water and other substances into the digestive tract. The entire midgut is called the ventriculus, which is the first part of the digestive tract responsible for secreting enzymes to digest food and absorb nutrients. The digestive cells on the wall of the ventriculus have tiny projections (visible only under a microscope) called microvilli that increase the surface area for absorption of nutrients.
The midgut is formed from the embryonic endoderm and is not protected by an intima structure, but is instead lined and protected by a semipermeable membrane called the trophoblastic membrane secreted by a bundle of cardiac epithelial cells (cardial epithelium) located just behind the foregut valve (valve cardia). The structure of the trophoblastic membrane consists of chitin microfibrils surrounded by a carbohydrate protein matrix.
The posterior aspect of the midgut is marked by another sphincter called the pyloric valve. This valve regulates the flow of material from the midgut to the hindgut.
c) Hind intestine
The pyloric valve marks the beginning of the hindgut and is also the starting point of the malpighian ducts, long, tubular structures distributed throughout the abdominal cavity that serve as excretory organs to remove nitrogenous waste products (mainly ammonium ions, NH 4 + ) from the blood (hemolymph). Ammonium ions are converted to urea and then uric acid by a series of chemical reactions in the malpighian ducts and are then released into the hindgut to be excreted with the feces.
The hindgut plays a major role in reabsorbing water and salts from the waste products of the digestive tract. In some insects, the hindgut is divided into three observable regions: the ileum, the colon, and the rectum. Water reabsorption is assisted by six rectal cushions located in the rectum wall that retain more than 90% of the water in the feces before it is excreted through the anus.
Tank
saliva
Right
Esophagus
Foregut intima layer
Tooth
Small kite
Anterior bowel valve
Tube
Malpighi midgut
Pyloric valve
Ileal and colon
Hindgut intima layer
Almost
Anus
Lower throat
Straight intestine
Upper lip
Anterior oral cavity
Lower lip
Saliva duct
Left salivary gland
Left salivary gland
Stomach muscle
Solid bowel
Pyloric ball
Potential membrane
Figure 4.1: General digestive and excretory systems of insects (according to William
S. Romoser and John G. Stoffolano, Jr).
2.3. Circulatory system
Insects and other arthropods have an open circulatory system that differs from the closed circulatory system of humans and other vertebrates in both structure and function. In a closed circulatory system, blood is always contained in reservoirs such as arteries, veins, capillaries, and the heart. In an open circulatory system, blood (called hemolymph) flows freely within the body cavity, in direct contact with all internal tissues and organs.
a) Function
In addition to basic functions such as transporting nutrients, salts, hormones, and metabolic waste throughout the body, the insect circulatory system also performs other important roles:
- Protect the body: such as healing wounds by clotting reaction, gathering and destroying endoparasites.
- Produces self-defense compounds to fight against predators.
- Create internal pressure to support egg hatching; larval moulting; adult emergence; expansion of body and wings after moulting and emergence; physical movement (especially in soft-bodied larvae); reproduction (fertilization and egg laying); and swelling of exocrine glands.
- In some insects, blood (hemolymph) also aids in thermoregulation: cooling the body by transferring heat away from areas where muscles are actively working, and warming the body by collecting and transporting heat absorbed during sun exposure to areas of the body where it is needed.
b) Structure
Structurally, the insect circulatory system consists of dorsal blood vessels and blood sinuses.
+ Back blood vessels
The dorsal blood vessel is the major organ responsible for transporting blood in the circulatory system and consists of a tube running along the thorax and abdomen located inside the dorsal wall of the body. In most insects, the dorsal blood vessel is a fragile membranous structure that collects blood in the abdomen and carries it forward to the head.
In the ventral region of the dorsal blood vessel is called the heart. Here it divides into cardiac chambers, each corresponding to an abdominal segment, separated by heart valves (ostium) to ensure unidirectional blood flow. On either side of the cardiac chamber wall there is a pair of alary muscles. Contraction of the alary muscles helps push blood forward from one cardiac chamber to the other. The rate of contraction of the heart varies depending on the insect species (typically 30–200 beats per minute) and the air temperature. The heart rate increases at high temperatures and decreases at low temperatures.
In front of the heart (thoracic region), the dorsal blood vessels have no valves and muscles but are simply a tube called the aorta that runs forward into the head and empties near the brain. Blood bathes the organs and muscles of the head as it exits the aorta, then spreads back through the digestive tract and body into the abdomen to the heart to complete a circuit.
Auxiliary pump
Dynamic
Pump circuit
owner
extra
Pump Root Auxiliary Slot Heart Heart
dorsal membrane
Root of the foot
Membrane
Figure 4.2: Diagram showing the blood circulation of insects in the body
+ Blood sinus
To aid in the movement of blood, the body cavity is divided into three chambers called blood sinuses by two membranes (the dorsal and peritoneal membranes). The dorsal membrane, formed by the alary muscle of the heart and similar structures, separates the cardiac sinus (pericardial senus) from the visceral sinus (perivisceral sinus). The peritoneal membrane, always covered with nerve fibers, separates the visceral sinus from the perineural sinus.
c) Blood components
About 90% of insect blood is plasma, a colorless, sometimes greenish or pale yellow liquid. Compared with vertebrate blood, insect blood has higher concentrations of amino acids, proteins, sugars, and inorganic ions. Overwintering insects often store ribulose, trehalose, or glycerol in their plasma to help prevent their blood from clotting in cold temperatures.
The remaining 10% of the blood volume is made up of various types of cells (collectively called hemocytes) including phagocytes and exocytes. Except in some species of flies and mosquitoes, insect blood does not contain red blood cells. Oxygen supply in insects occurs directly through the tracheal system, not through the circulatory system.
2.4. Respiratory system
Insects are aerobic organisms, they need oxygen from the environment to live.
The respiratory system is responsible for supplying oxygen to all cells and removing carbon dioxide (CO 2 ) from the body. Unlike vertebrates, the insect respiratory system is separate from the circulatory system, and is a complex network of tracheal tubes that deliver oxygen to all cells in the body.
Air enters the insect body through openings called spiracles located along the sides of the thorax and abdomen of the exoskeleton. In most insects, each pair of spiracles is located on a body segment. The flow of air into and out of the insect body is regulated by one or two flap-like valves located near the opening of the spiracles. These valves are controlled by muscles, which close the spiracles when the muscles contract and open them when the muscles relax.
After passing through the spiracles, air enters a longitudinal tracheal tube called the tracheal trunk, which then diffuses into a complex network of tracheal tubes that divide into increasingly smaller branches that reach all parts of the body. At the end of each tracheal branch, a special cell (tracheole cell) provides a thin, moist surface for gas exchange between air and living cells. Oxygen in the trachea is first dissolved
into the fluid of the tracheole and then diffuses into the cytoplasm of an adjacent cell. At the same time, CO 2 , produced as a waste product of cellular respiration, diffuses out of the cell and eventually out of the body through the tracheal system.
A
Chest airbag
Heart Breathing Hole
Windpipe
Lateral tracheal body
Branch
windpipe
Abdominal air bag
Dorsal trachea
Close | Branch | Close | ||
Bag | gas | gas | gas | Gas |
gas | manage | manage | manage | manage |
belly | beside | back | back | belly |
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Head trachea
B
Thoracic vent
Tracheal branch
belly
Abdominal trachea
Abdominal breathing hole
Figure 4.3: Diagram showing the tracheal system of an insect (grasshopper).
(A) dorsal view; (B) ventral view
To prevent the trachea from collapsing under pressure, thin strands of epidermal tissue (taenidia) coil like a spring around the membranous wall of the trachea. This structure allows the trachea to bend and stretch without constricting the flow of air.
In some parts of the tracheal system, taenidia are absent, allowing the formation of bladder-like sacs to store air. In dry environments, the temporary air supply of these sacs allows insects to
Parasites can retain water in their bodies by closing their spiracles during periods of high transpiration shock.
Aquatic insects consume the air stored in their air sacs when diving, or use the stored air to regulate buoyancy. During molting, the air sacs inflate, allowing the insect to shed its old exoskeleton and expand its new one. Between molts, the air sacs provide space for internal organs to expand.
Body wall
Epithelial cells
Tracheal wall with epithelial cells removed
Intimate layer
Tracheal tube
Breathing hole
Tracheal body
Windpipe
Tracheal branch
Figure 4.4: Tracheal system of insects
a) Respiration of insects living on land
Small insects respire almost exclusively by passive diffusion and physical action for gas transport in the tracheal system.
In large insects, respiration requires active ventilation of the tracheal system (especially when the insect is active or is under thermal shock) by opening and closing several spiracles while using abdominal muscles to expand and contract the body volume. Although this type of activity can help push air along the body along the tracheal shaft, diffusion is still important to deliver oxygen to individual cells through the network of small tracheal tubes. In fact, the rate of gas diffusion is one of the main limiting factors (along with the weight of the exoskeleton) that prevents insects from growing too large.
b) Respiration of insects living in water
Insects that live in water also need oxygen, so they have breathing patterns that are adapted to the environmental conditions in which they live. Some breathing patterns of insects that are adapted to living in water are as follows:
+ Cuticular respiration