OF WASHINGTON, VOLUME XI, 19(19. 151 



NUPTIAL COLORS IN THE CHRYSOMELID^E. 



[Coleoptera.] 

 BY FREDERICK KNAB. 



Among certain forms of Chrysomelidse the imago takes on 

 an entirely different appearance with the attainment of sexual 

 maturity. Either new colors are added to the existing pattern 

 or there is a complete change in coloration. These colors are 

 not acquired as the result of the more or less gradual chiti- 

 nization and pigmentation which follows eclosion ("Aussfarb- 

 ungsprozess" of the Germans) hut make their appearance 

 only with the development of the sexual powers. This matur- 

 ing of the sexual powers may be a matter of months and often 

 it only comes about with the advent of another season, for most 

 Chrysomelidae are single-brooded and do not become sex- 

 ually mature until after they have hibernated or aestivated. 

 Perhaps it would be more exact to say that the physiological 

 changes which determine sexual activity take place during the 

 resting period (hibernation or aestivation ). 



One of the most striking examples of color-transformation 

 of this character has been studied by Caulfield in a northern 

 species of Cassidini; its significance, however, appears to have 

 been wholly overlooked. The beetle in question is Physonota 

 helianthi Randall. The difference between the parent beetles 

 and the new generation produced from them is so great that 

 Caulfield very naturally concluded the insect to be double- 

 brooded and dimorphic.* l>ut further observation demon- 

 strated that this insect is single-brooded and in the course of 

 time completely changes its appearance. f The beetles which 

 appear in the spring or early summer are brilliant golden green 

 and so they remain until they copulate, lay their eggs, and final- 

 ly die. The offspring of these golden green parents are wholly 

 different in appearance. After emergence the pronotum and 

 elytra are shining creamy white with translucent marginal 

 portions and with five black spots upon the pronotum ; soon, 

 with the progressing chitinization, the elytra change to a dull 

 blackish color with irregular ivory spots and blotches upon 

 them. In this sober garb the beetles may be found upon their 

 food-plant during the later part of the summer and in the 

 autumn; they feed but little and show no sexual desires, and 

 it is in this state that they go into hibernation. When the 

 beetles reappear in the following spring they have assumed the 



*Can. Ent., vol. 16, p. 227 (1884). 

 fCan. Ent., vol. 19, p. 73 (1887). 



