PREVENTION AND DESTRUCTION OF INSECT PESTS. 487 



the egg-stage in the Winter months. Thus the importance of know- 

 ing the life-historiea of our insect and other pests. 



Nearly every hnovon flant u attached by some insect. — Very often 

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

 attacks the onion, the riist or carrot fly the carrot, the American 

 blight the apple (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 Cruciferee alike. Some of 

 our worst pests are cosmopolitan 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 breathing apparatus, and the organs of 

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

 first is modified for biting, 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 this proboscis 

 into the leaf, and when inserted open it and draw out the sap. 

 Sucking-mouthed insects have a long, soft, coiled proboscis, and can 

 do no harm. Lepidoptera have sucking mouths. 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 larv83, and so destroy them. The plant-louse 

 would plunge its beak through the poison before it opened, 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 

 breathing-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, only by using some spray that will block up these breathing- 

 pores : soft-soap answers this purpose; any other substance, such as 



