. Elementary entomology . In aquatic insects various respirator}- devices have been developed. Many of them (May-fly, dragon-fly, stone-fly, and mosquito nymphs) bear tracheal gills which consist of a leaflike expansion, or a tuft of thin filaments, into which the trachea extend and divide into a fine network. The oxygen of the water passes through the gill mem- brane into the air of the trachea, and thus the air of the tracheal system is purified. Xo true gills,- -that is, gills carrying blood vessels, like those of fishes, - - are found in insects. Other aquatic insects carrv a thin film of
. Elementary entomology . In aquatic insects various respirator}- devices have been developed. Many of them (May-fly, dragon-fly, stone-fly, and mosquito nymphs) bear tracheal gills which consist of a leaflike expansion, or a tuft of thin filaments, into which the trachea extend and divide into a fine network. The oxygen of the water passes through the gill mem- brane into the air of the trachea, and thus the air of the tracheal system is purified. Xo true gills,- -that is, gills carrying blood vessels, like those of fishes, - - are found in insects. Other aquatic insects carrv a thin film of air with them, either bv means of a ./ * thick coating of fine hairs to which air bubbles adhere, or beneath the wing-covers. The trachea are sometimes prolonged into tubes which pro- ject beyond the tip of the abdomen and extend to the surface of the water or mud in which these insects live. From the above description it is evident that insects possess the best-developed type of respir- atory system, extending as it does to all the tissues of the body, giving them a constant Fl(. Diagram supply of fresh air and earning off the waste of trachea in head gases. \Yith an,ample food supply this makes possible a rapid oxidation of the tissues, and '. trachea, or air tubes. ..... r i Note branches to all undoubtedly is one of the chiet reasons lor the the mouth-parts and wonderful muscular activity, working: power, and the antennae. (After Miall and Denny) endurance or insects. The structure of the respirator)7 system is of great practical im- portance in combating insect pests. Many insects which cannot be destroyed with arsenical poisons are killed by contact insecti- cides in either a spray or a dust form. These contact insecticides destroy the insect by entering or clogging the spiracles or trachea. Oils are particularly valuable because they spread and pass readily through the hairs which guard the spiracles. Soap solutions leave a gummy deposit, when the water evaporates, which
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