PHYSIOLOGY OF WING DEVELOPMENT IN APHIDS. IOQ 



present. There is, however, no external indication of the wings 

 or of their buds. The body is almost columnar, with a con- 

 striction back of the head, but with no marked differentiation 

 between the thorax and abdomen. 



In those individuals which ultimately become winged, the 

 second and the third thoracic segments begin to swell laterally 

 as well as dorso-ventrally. The swollen thorax is ordinarily 

 noticeable at the end of the first ecdysis in the case of the rose 

 aphids. Usually after the second, yet occasionally after the 

 third ecdysis, in the case of the mustard aphis, a pair of hyaline 

 wing-pads protrude from each side of the second and third tho- 

 racic segments. At the following ecdysis, the wing-pads become 

 unfolded and the adult insect results. In those forms which 

 remain apterous, no constriction between the thorax and abdomen 

 occurs. 



Other structural differences noticeable between the apterous 

 and alate viviparous females of the common rose aphid, Macrosi- 

 phum roses (L.), may be tabulated as follows: 



Winged Viviparous Female. Wingless Viviparous Female. 



Color Dorsal marking present. Dorsal marking absent. 



Length 2.2 mm. 2.7 mm. 



Antenna Articles I to VI dark through- Only 1,11, and VI dusky. 



out. 



Sensoria on III More than 60 found About 12, all being found near the 



throughout the entire length. basal portion. 



Color of Cornicle Dark throughout. Dark with lighter rings near the base 



and apex. 



These are some of the more prominent differences. Minor 

 differences, as, for example, the relative length, shape, size, etc., 

 of the cornicle, cauda, antenna, etc., are numerous and cannot be 

 enumerated here. It follows, then, that the factor which is 

 responsible for the production of either the apterous or the alate 

 forms not only determines the fate of the wings, but also causes 

 other morphological changes as above mentioned. 



Although no special effort was made to study the histological 

 differences between the two forms, the sectioned material 

 showed that there is a less amount of muscles and ectodermal 

 cells, but more of fat body in the apterous form as compared 

 with the alate individual. 



