466 



N. M. Stevetjs 



TABLE II 

 Diahrotica l2-punctata 



It will be seen from the tables that Diabrotica soror is somewhat 

 more variable and averages smaller in early summer than in late 

 autumn; also that there is a possibility of two or three intergrading 

 groups. The latter fact would not, however, seem to have any 

 significance with reference to the supernumerary chromosomes, 

 since in Diabrotica 12-punctata (Table II) the curve of variability 

 is very steep with one mode at 5 mm. The 100 specimens of 

 Diabrotica 12-punctata included in Table II were collected on some 

 late goldenrod in one corner of a field on October 3, 4 and 9; the 

 first 100 in Table I, in one rose garden in small collections extend- 

 ing over about six weeks. In both lots, most of the insects had 

 recently emerged, and the conditions of temperature and nutrition 

 under which they had developed could not have varied very 

 greatly. 



The one significant result so far as the supernumerary chromo- 

 somes are concerned is the parallel series of numbers for the five 

 types of the two species — Diabrotica soror, 48, 33, 15, 3, I and 

 Diabrotica 12-punctata, 51, 35, 11, 2, i. Were it not for this par- 

 allehsm of results in the two similar but geographically widely 

 separated species,^ one might suppose the presence of the super- 

 numeraries to be accidental, due perhaps to an irregularity in the 

 breaking up of the spireme or to imperfect metakinesis some- 

 where in the history of the male or female germ cells. The behav- 

 ior of the supernumeraries in the growth stages of the spermato- 



1 Diabrotica 12-punctata occasionally ranges into California, but belongs more especially to the eastern 

 half of the United States, being perhaps most abundant in the Mississippi Valley. 



