10 INSECTS INJURIOUS TO STAPLE CROPS. 



The typical jmpa (Fig. 2, c, d) of a butterfly or moth is 

 of a more or less oval shape, rather resembling the adult 

 insect than the larva, with the wings and antennae tightly 

 folded at the sides, the legs drawn up snugly together under 

 them, and the head and mouth-parts bent upon the breast, 

 or sternum. But all of these parts are not always recog- 

 nizable, the legs and mouth-parts being sometimes lacking. 

 Gradually the jidult insect develops, and at last the pupal 

 skin is broken open and the airy butterfly emerges to enjoy 

 a short life and perpetuate the species. Such a series of 

 transformations is that commonly found among butter- 

 flies and moths (Lepidoj)tera), beetles (Coleoptera), flies 

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

 complete metamorphosis. All of these insects normally pass 

 through four stages, the Qgg, larva, pupa, and adult. 



Incomplete MetamorphosU. — 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 

 agg. 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 having fully developed 

 wings, being larger, and often by an accompanying change 

 of markings. The immature stages of such insects are 

 called nymphs^ and this development an incomplete meta- 

 'inorpliosis, having but three stages, the Qgg, nymph, and 

 adult (Fig. 3). 



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. 



