CHAPTER XVII 



INSECT PESTS 



How insects injure plants. After the young plants have 

 broken through the soil with every indication of becoming 

 thrifty and fruitful specimens, or after older and well-estab- 

 lished plants have given indications of an abundant crop, a 

 multitude of fungous and insect pests have still to be reckoned 

 with by the gardener before a return for his labor is assured. 

 Nearly all the insects that prey upon cultivated plants are so 

 voracious and multiply in such numbers that the crop is some- 

 times destroyed in spite of every effort of the gardener to pre- 

 vent it. It is estimated that insects and plant diseases cause 

 more than a billion dollars' damage to crops each year. As 

 regards the way in which they injure crops, insects may be 

 divided into two groups those with mouth parts adapted to 

 chewing, and those with mouth parts adapted to sucking. The 

 chewing insects harm the plants by eating stems and foliage, 

 or by burrowing into fruits, stems, and other plant parts. The 

 sucking insects do not defoliate the plant, but by sucking the 

 juices from the tender tissues they are nearly or quite as harm- 

 ful. Chewing insects may be controlled by poisons, but such 

 substances have no effect upon sucking insects whose food 

 comes entirely from the interior of the leaf. These latter must 

 be fought with smothering sprays and gases. 



Metamorphoses of insects. There are two general lines along 

 which insects develop from the egg to maturity. In grasshop- 

 pers, crickets, katydids, and the like, the newly hatched insect 

 has considerable resemblance to adult forms and gradually 

 acquires the characters of maturity as it grows in size. Such 



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