PKKVENTION AND DESTEUOTION OF INSECT PESTS. 511 



of a few may be destroyed in winter. Thus the importance of 

 knowing the life- histories of our insect and otlier pests. 



Nearly every known plant is attacked by some insect. — Very often 

 each species of insect has a particular food-plant : the onion fly 

 only attacks the onion, the rust or carrot fly the carrot and parsnip, 

 the American blight the apple and hawthorn (seldom the pear). 

 More generally any member of the same family of plants is attacked 

 by one species of insect ; for example, the turnip flea infests all 

 Gruciferfe alike. Some of our worst pests are general feeders, such 

 as the wireworm and leather-jacket, which will feed off the roots 

 of nearly all plants. Where we get one species feeding only off one 

 particular plant or family of plants, we can do much to prevent their 

 damage by judicious rotation in the garden and in field cultivation. 



Three of the most important structural features to he considered in 

 regard to insect eradication and prevention of their attacks are the 

 structure of the mouth, the hreathing apparatus, and the organs of 

 sense. — There are three distinct types of mouth found in insects : 

 the first is modified for hiting, the second for piercing, the third for 

 sucking. Insects provided with a biting mouth devour plant-tissue 

 wholesale, both leaf, stem, and rootage being subject to their on- 

 slaughts. Piercing -mouthed insects have their mouth-parts drawn 

 out into needle-shaped lancets enclosed in a tube formed by the 

 upper and lower lips. These insects feed by plunging the proboscis 

 into the leaf and drawing out the sap. Sucking -mouthed insects have 

 a long, soft, coiled proboscis, and can do no harm. Lepidoptera 

 have sucking mouths, but some few in Africa, &c., have the pro- 

 boscis so hardened they attack fruit. This structure of the insect 

 mouth is a point too often neglected by people anxious to destroy 

 insects. Poisons such as arsenical washes are useless for piercing- 

 mouthed insects such as plant-lice and bugs ; on the other hand, 

 poisons that will hold to the leaf will be taken in by leaf- and 

 blossom-eating larvae, and so destroy them. The plant-louse would 

 plunge its beak through the poison before it used, and so escape its 

 ill effects ; to poison plant-lice we should have to poison the sap. 

 How, then, can we destroy such pests ? On examining any insect 

 we shall observe (as pointed out in chapter vii.) at the sides of the 

 body a number of oval or slit-like apertures : these are hreathing- 

 pores or spiracles. Insects do not breathe through their mouth, but 

 through these respiratory openings. Varnish these over, and the 

 insect will be asphyxiated. Plant-lice, &c., can be killed, then, 

 by using some spray that will block up these breathing - pores : 



