. Elementary entomology . In aquatic insects various respiratory 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. No true gills, — that is, gills carrying blood vessels, like those of fishes, — are found in insects. Other aquatic insects carry a thin film of air
. Elementary entomology . In aquatic insects various respiratory 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. No true gills, — that is, gills carrying blood vessels, like those of fishes, — are found in insects. Other aquatic insects carry a thin film of air with them, either by 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 supply of fresh air and carrying off the waste gases. \\'ith an ample food supply this makes possible a rapid oxidation of the tissues, and undoubtedly is one of the chief reasons for the wonderful muscular activity, working power, and endurance of insects. The structure of the respiratory 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 clogs the trachea. Finely divided dusts, such as fine tobacco dust, pyrethrum, and even air-slaked lime or road dust, will clog the spiracles of man
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Keywords: ., bookcentury1900, bookdecade1, booksubjectentomology, bookyear1912
