. Animal biology. Zoology; Biology. CLASS INSECTA 289 flea seems to be the agent in the transmission of bubonic plague from rats to man. 318. Combating Injurious Insects.—Injurious insects may be com- bated in many ways. Mandibulate insects can be destroyed by placing poisoned food where they will get it or by spraying poisons in solution on the leaves or fruit of plants which they eat. This method can be applied in the case of cockroaches, crickets, earwigs, ants, beetles, and lepidop- terous larvae. Suctorial insects may be sprayed with oily substances which close the spiracles and cause suf
. Animal biology. Zoology; Biology. CLASS INSECTA 289 flea seems to be the agent in the transmission of bubonic plague from rats to man. 318. Combating Injurious Insects.—Injurious insects may be com- bated in many ways. Mandibulate insects can be destroyed by placing poisoned food where they will get it or by spraying poisons in solution on the leaves or fruit of plants which they eat. This method can be applied in the case of cockroaches, crickets, earwigs, ants, beetles, and lepidop- terous larvae. Suctorial insects may be sprayed with oily substances which close the spiracles and cause suffocation, or if they are in a room where they can be reached with poisonous gases, they may be destroyed by fumigation. Insect powders usually produce their effects by being. Flo. 188.—Australian lady-beetle, Rodolia cardinalis Mulsant, and the scale insect on which it feeds, Icerya purchasi Maskell. A, the adult beetle; B, the pupa; C, larvae feeding on the scale insect; D, a twig of orange, showing the scale lice, and larvae and adults of the beetle. A to C, X 4; Z), natural size. {From Marlatt, Year-book, U. S. Dept. Agr., for 1896.) breathed into the tracheal tubes. In some cases insect pests may be secured in numbers by jarring the plants and collecting them in appro- priate hoppers, after which they may be killed in the manner most convenient. Insects may be trapped in a number of ways and may be combated by the spreading of infectious diseases among them. The most important factor in insect control, however, is their destruction by birds, and to this end insectivorous birds should be zealously protected. 319. Beneficial Insects.—Both the larvae and the adults of the order Odonata (o do na' ta; G., odontos, tooth), which includes the dragon flies and damsel flies, are carnivorous, the adults being beneficial because of their destruction of mosquitoes, which form a large part of their food. Some beetles are beneficial because they attack injurious insects. Among thes
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