Fundamentals of Entomology

Anatomy: Respiratory system

Respiratory system

• The insect respiratory system is made up of a series of tubes that originate from spiracles (openings of the exoskeleton that allow for gas exchange) and extend throughout the body. Internally, the tubes, or trachea, appear as thin white lines throughout the hemocoel and are particularly noticeable surrounding internal organs. Trachea deliver oxygen to internal organs and tissues.

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• Compare the tracheae with the Malpighian tubules. They are often very similar in appearance. Did you confuse tracheae with Malpighian tubules earlier?
• Two ways to distinguish the structures are color and location. Tracheae have a ‘shinier’ appearance under the scope and may even appear ‘silvery’. As for location, Malpighian tubules are found at the junction of the midgut and hindgut (although they may extend outward into the hemocoel), whereas tracheae are positioned throughout the body.

Respiratory system
Similar to aerobic animals, insects must obtain oxygen from their environment and eliminate carbon dioxide respired by their cells. This is gas exchange through series of gas filled tubes providing surface area for gaseous exchange (Respiration strictly refers to oxygen-consuming, cellular metabolic processes). Air is supplied directly to the tissue and haemolymph (blood) is not involved in the respiratory role. Gas exchange occurs by means of internal air-filled tracheae. These tubes branch and ramify through the body. The finest branches called tracheole contact all internal organs and tissues and are numerous in tissues with high oxygen requirements. Air usually enters the tracheae via spiracular openings positioned laterally on the body. No insect has more than ten pairs (two thoracic and eight abdominal).
Based on the number and location of functional spiracles respiratory system is classified as follows
1. Holopneustic:10 pairs, 2 in thorax and 8 in abdomen. e.g. grasshopper
2. Hemipneustic: Out of 10 pairs, one or two non-functional
3. Peripneustic: 9 pairs - 1 in thorax 8 in abdomen e.g. Caterpillar
4. Amphipneustic 2 pairs - One anterior, one posterior, e.g. maggot.
5. Propneustic: 1 pair -anterior pair e.g. Puparium
6. Metapneustic: 1 pair - posterior pair e.g.Wriggler
7. Hypopneustic:10 pairs - 7 functional (1 thorax + 6 abdominal), 3 non functional. e.g. head louse
8. Apneustic: All spiracles closed, closed tracheal system e.g. naiad of may fly.