In insects, respiration occurs through
Insect respiratory system comprises extensive internal tracheal network opening externally via paired spiracles with valvular closure mechanisms on thorax and abdomen. Spiracles lead to atria and tracheae reinforced by spiral taenidia preventing collapse, branching repeatedly into finer tracheoles terminating near mitochondria, delivering air directly to tissues, bypassing circulatory system. Abdominal pumping ventilates sacs, discontinuous gas exchange minimizes water loss. Book lungs typify spiders, gills crustacean larvae and some aquatic nymphs have tracheal gills, skin diffusion occurs only in minute collembolans. Tracheal system enables high flight metabolism and terrestrial colonization.
Ref: Campbell Biology, 12th ed., Chapter 42: Insect Tracheal System; NCERT Class 11, Chapter 7