63 The Mechanism of Evolution in Leptinotaesa 



Habitat, Ecology, Life Histobt. 



Like the other species in this division L. decemlineata passes the winter as an 

 imago, hibernating, but there is a great variation over the area inhabited in the 

 dates of entrance into and emergence from hibernation, due almost entirely to 

 varying climatological conditions. On emergence it breeds, giving the first 

 summer generation, which emerges about the middle of July over most of its 

 range, and these breed again, giving the second summer generation, which 

 emerges in August or early September and soon hibernates. It is not uncom- 

 mon to find a third small brood, especially in the south, and in favorable seasons 

 in other places, and this due to the fact that in nature the overwintering popu- 

 lation may live and breed with the second summer generation, producing hybrids 

 between generations of different potentialities. The progeny of these matings 

 often numerous and strong, behave in a very curious and variable manner, so 

 that in materials in nature, two, three, or even four broods are foimd at times. 

 When, however, stocks from many different portions of the country are fully 

 analyzed, it is found that all, both north and south, are two-brooded like the rest 

 of the species in this division. 



MiNOB Divisions. 



Many years of breeding and experimentation have shown that an endless 

 number of true-breeding races of low variability can be created in experiment. 

 ISTone of these are well defined, or of any independence in group-cultures or in 

 nature, and none has any homologue in nature. All are due to purely artificial 

 isolations and fixings of trivial variations of attributes present, and while an 

 imposing array of pure biotypic lines could be created, it would be the acme of 

 folly to do so, because they have no discoverable permanence in the species in 

 nature. 



Sports are known sparingly in nature. In 1906 I recorded the occurrence of 

 several which were then regarded as such, some of which proved on breeding to 

 be gametic variations, and it is only by breeding that the real nature of these 

 variations can be determined. It is not uncommon to find somatogenic varia- 

 tions, some of which closely resemble the germinal variations. Breeding tests 

 alone can determine the true nature of these extreme variations. 



Spobts Obseeved in Natuee and Tested by Bbeedino. 



LEPTINOTABSA pallida NOV. VAB. 



(Plate 6, flg. 2.) 



Imago : Oval, convex, more elongate than decemlineata Say, white or faintly 

 yellow- white ; smaller than L. decemlineata Say, with sides more nearly parallel. 

 Above: Epicranium sparingly, irregularly, and not deeply punctate, densest 

 behind eyes, center polished, few punctations, color pale white with tinge of 

 yellow, pattern extremely reduced, but center usually variable; eyes black, 

 mouthparts pale; mandibles, tips brown or black; antennae, four basal joints 

 white, remainder very light brown, faintly pubescent, seventh sharply broadened, 

 broad as long, as are also eighth to eleventh, twelfth conical, rounded. Pro- 

 notum, few small scattered pimctations on lateral and posterior margin, whole 

 part polished; pattern reduced, elements all present, but fusions are rare. 

 Pronotum, distinctly longer and narrower than in L. decemlineata Say; scu- 

 tellum smooth, polished, brown, edges darkened; elytra white or pale yellow- 



