26 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



Such a series of transformations is that commonly found among 

 butterflies and moths (Lepidoptera), beetles (Coleoptera) , flies 

 (Diptera), and bees (Hymenoptera), and is known as a complete 

 metamorphosis. All of these insects normally pass through 

 four stages, of egg, larva, pupa, and adult. 



Incomplete Metamorphosis. In contrast to this mode of 

 development is that of the grasshoppers (Orthoptera), bugs 

 (Hemiptera), and some other insects. As already stated, these 

 are much like the adult upon emerging from the egg. With 

 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, of egg, nymph, and adult 

 (Fig. 16). 



The time occupied by the complete life-cycle 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, 

 therefore, never kill. 



Insects may be roughly divided into two classes, those which 

 bite and those which suck their food. Among the former are 

 the beetles, grasshoppers, the larvas of butterflies and moths, 

 and the larvse of saw-flies ; and among the latter are butterflies, 

 flies, bees, and bugs, while the larvae of most flies and bees do not 

 possess mouth-parts homologous with those of the above. 



