266 JOURNAL OF AGRICULTUEE OF P. R. 



GENERAL CONSIDERATIONS. 



Before taking up a discussion of any one particular insect in its 

 relation to vegetables it would be well to consider the subject of 

 insects in general, their differences in structure and habits, and the 

 significance of these factors with regard to the methods employed to 

 control them. 



Insects may be roughly divided into two general classes, those 

 possessing biting mouthparts and those with sucking mouthparts. 

 To the first class belong grasshoppers, leaf-feeding beetles, and cater- 

 pillars. To the second, such insects as plant lice, scale-insects, bees, 

 and true bugs. Insects of the first class may usually be destroyed 

 by the use of stomach poisons, but this form of control is useless for 

 the second class, which must be hit by a contact spray in order to be 

 killed. 



Most insects pass through a number of different changes in form 

 before becoming adults. Some such as the grasshoppers and true 

 bugs have what is known as an incomplete metamorphosis. They 

 hatch from the egg into forms resembling the adults, but differing 

 usually in size and in lacking certain organs such as wings. This 

 stage between the egg and adult is known as the nymphal stage. 

 Other insects such as the. butterfly, beetle, and bee have what is 

 known as a complete metamorphosis. On leaving the egg thej' assume 

 a form entirely different from the adult. This is the larval or grub 

 stage, an active feeding stage. After this stage they change to a 

 pupal or resting stage, and finally to the adult forms. 



These stages differ remarkably in form and habit in the different 

 species of insects. Some are passed in the soil, others in the air, 

 some on the foliage of plants, and some within the stems and tissues 

 of the host plant itself. 



A careful study of all stages in the life of an insect will usually 

 reveal a weak spot, and advantage may be taken of tliis in controlling 

 the pest. 



CONTROL MEASURES. 



Control measures are numerous and varied, but may be all roughly 

 classified under the two main groups, direct and indirect. 



Indirect measures are mostly preventive and consist of any prac- 

 tice that does away with conditions favorable to injurious insect 

 life. Clean cultivation, the destruction of weeds and trash that 

 harbor destructive insects, the intelligent rotation of crops, the 

 planting of clean seed, the use of hardy seedlings, the proper use of 



