Study On"Lungs" Of The Insect Respiratory System

Most of insects usually don not have the hemcoyte for transporting oxygen, the respiratory of insect is chiefly accomplished by the tracheal system that spreads all over the whole body. Outside oxygen enters the tracheal system through spiracles arranged in two sides of body and is transported through trachea and tracheoles to meet directly the needs of tissues. But Locke(1998), a Canadian entomologist, recently suggested that caterpillars have evolved "lungs" for hemocyte gas exchange. The "lungs " are located at trachea of the 8th pair of abdominal spiracles and tokus compartment at the tip of the abdomen. This is a new concept of insect physiology. Based on his research, the structure and function of "lungs" are studied by means of electron microscope and other chemical methods further. The generality of "lungs" existence in the order Lepidoptera and the Class Insecta and evolutionary relationship are probed into. The main results are as follows:1. The structure and function of "lungs" of larvae Sylepta derogata and Leucania separata Walker are: ① "lungs" are located at trachea of the 8th pair of abdominal spiracles and the tokus compartment. The spiracles are bigger and more near dorsal line than all the others. Their trachea branches are taper and abundant and form short tracheoles. This gave the tufted form to the trachea, which appeared shrubby. The trachea branches that arranged in other segments gave them a tree-like look. They do not directly supply oxygen for tissues, but they suspend in the hemolymph and attach to the muscle of the heart, so that they can move in constant with the contraction of the heart muscle. ②The 8th segment tracheal tufts have thinner cuticle and basal lamina than that of the other trachea, and have much pad cuticle, which is appropriate for them to move, and their basal lamina have small pores, which are favour of the permeation of gas. ③Injecting the methylene blue into the larvae to label hemolymph, we observed that the hemolymph flow into the heart through the 8th segment tracheal tufts. ④Normally these tracheal tufts have all kinds of hemocytes, which are abundant in the tufts. A large number of hemocytes released from tissues attach to the tufts by changing their structure when anoxic stress happen. It is favour of the exchange of gas. ⑤Injecting leucomethylene blue into the larvae, we can find that the tufts easier change into blue than the others. It suggests that oxygen is more readily available to the hemolymph in 8th segment. Above the characters indicate that the tracheal tufts have large contact area with hemocoel, thinner cuticle, the participation of the homocytes, and the higher ability to gain oxygen and so on. Therefore, the tracheal tufts have the function of the lungs.2. The studies on the larvae of 43 species, belonging to 19 families of Lepidoptera indicate that existence of "lungs" as general. With the development of evolution from lower to higher the structure of the "lungs" have an evolution course from unclear to clear and finally very clear.3. The studies on the nymphs or larvae of 18 species belonging to Orthoptera, Mandotea, Homoptera, Hemiptera, Coleptera, Diptera and Hymenoptera indicate that the larvae of Argridae (Hymenoptera) have the function of "lungs", but the nymphs or larvae of other orders may not have "lungs".4. The structures of the "lungs" have an evolution trend from lower to higher through Lepidoptera to Hymenoptera.5. If the function of the "lungs" is extended into to "aerating trachea", the larvae of Apidae (Hymenoptera), Muscidae (Diptera) and nymphs of Coleoptera, Hemiptera also may have the function of the "lungs".Our researches are supplement and support to Locke's researches and an important progress in insect physiology.