24 



INSECT PESTS OF FARM, GARDEN AND ORCHARD 



each molt they become larger and small wing-like pads gradually 

 appear on the sides of the thorax. There is no dormant or pupal 

 stage, the adult insect differing from the previous stages in hav- 

 ing fully developed wings, being larger, and often by an accompany- 

 ing change of markings. The immature stages of such insects 

 are called nymphs, and this development an incomplete meta- 

 morphosis, having but three stages, egg, nymph, and adult (Fig. 16). 

 The time occupied by the complete life^cle of an insect 

 varies from a week or ten days for the plant-lice to thirteen or 

 seventeen years for some cicadas, and is entirely dependent 

 upon the habit of the species and the climate. A correct knowl- 

 edge of the exact time and conditions under which the trans- 

 formations occur for each individual insect pest is therefore often 

 most essential when seeking means for its control. 



How Insects Feed 



The material to be used in combating a given insect is largely 



dependent upon the 

 structure of its mouth- 

 parts. Much Paris 

 green is wasted upon 

 insects unable to eat it 

 and which it will, there- 

 fore, never kill. 



Insects in ay be 

 roughly divided into 

 two classes, those which 

 bite and those which 

 suck their food. Among 

 the former are the 

 beetles, grasshoppers, 

 the larvae of butterflies 



FIG. 17. Front-view face of grasshopper (Schizto- and moths, and the 



cerca americana): ant., antenna; oc.. ocellus; i <? n' j 



ey., eye; cl, clypeus; Ibr., labrum, or upper larvae of saw-flies; and 



lip; mx.p., maxillary palpus; lab.p., labial pal- among the latter are 



' 10 fmaxilla; ' a6 -' labium ' or butterflies, flies, bees, 



and bugs, while the 



larvae of most flies and bees do not possess mouth-parts homo- 

 logous with those of the above. 



