152 COI.ORATION IN I.KPTINOTARSA. 



IN THE IMAGINES. 



In all the species of Leptinotarsa which I have studied, the development of 

 the imaginal color pattern begins in the latter part of the pupal stage and is 

 completed after emergence while the young imago is still in the pupal cell. 

 The full intensity of the adult coloration is not attained until after the beetle 

 has emerged from the ground and has been feeding for several days, that is, 

 just before it begins to breed. Soon after reproduction has commenced, how- 

 ever, the colors begin to fade. 



The Ontogeny of Coi^or on the Epicranium and Pronotum. 



The color patterns on the epicranium and pronotum begin to develop on the 

 average about three days before the final transformation ; but in some species, 

 and in individual instances, the time may be longer or shorter. Thus, in 

 decemlineata^ color may appear on the epicranium four or five days before the 

 insect emerges, while in oblongata, dilecta, and other species there may be no 

 trace of color upon these parts until ten or twelve hours before the final trans- 

 formation. 



The color development upon the epicranium of undecimlineata is typical 

 of those species which have a pattern composed of spots of dark cuticula color 

 upon a lighter background. On plate i8, figs. 9 to 14, are represented six 

 stages in this development. In the first stage (fig. 9) two lightly traced areas 

 upon the epicranium are observed as two faint yellow-brown spots. These 

 mark the beginning of the two centers (g and g') which in later stages fuse 

 to form a median heart-shaped spot. On the pronotum no color is yet visible. 

 A stage closely following this is represented in fig. 10, with the color on the 

 epicranium deeper and with two new faint yellow-brown areas on the prono- 

 tum in the position later occupied by the spots a and a\ Simultaneously two 

 color areas have appeared in the outer posterior portion of the epicranium, 

 which are the beginnings of the spots h and h\ In each of the spots a and a' 

 on the pronotum there are traces of anterior and posterior centers which are 

 usually visible for a brief period. In the third stage (fig. 11) the spots g and 

 g' have grown considerably larger and have fused across the median line pos- 

 teriorly, while h and h' have also grown and extended medianward. On the 

 pronotum a and a' have increased in depth of color and have spread peripher- 

 ally, while anteriorly new areas, the beginnings of b and &' and c and c\ 

 have appeared, and posteriorly e and e' are recognizable. In the following 

 stage (fig. 12), g and g' have grown larger and have also extended poste- 

 riorly until they almost unite with h and /i' in the median posterior portion of 

 the epicranium. This union is completed in the next stage (fig. 13). Upon 

 the pronotum d and d^ and / and /' now appear, and the a, b, c, and e spots 

 have grown in size and depth of color. In the remaining stages represented 

 (figs. 13 and 14) the color pattern is finished; g and g' completely fuse with 



