248 



HABITS AND INSTINCTS IN LEPTINOTARSA. 



number of the attributes of an animal, as, for example, all the color characters, 

 would fail to come directly under the influence of this kind of selection 

 because of their non-selective value, and their elimination or preservation 

 would therefore depend upon whether or not they were associated with some 

 character which did have a selective value to the species. 



TabIvE 107. — Selective action exerted upon L. decemlineata by the hibernation period. 



[Hibernation in the winter of 1903 to 1904 at Chicago, Illinois. The table is based upon the 

 species as a whole, and has been obtained by seriating the individuals into classes accord- 

 ing to their likeness to each other,] 



Period. 



Class. 



2 



3 



4 



5 



6 



7 



8 



9 



10 



II 



12 



13 



Before hibernation. 

 After hibernation . . 



0.5 



I 



1-5 



2 



3 



i 



19 



25 



42 



54 



21 

 19 



3 



I 



2 



I 



The species of this genus that live in the tropical or semi-tropical regions 

 also pass a portion of each year in a dormant state, which has been termed 

 aestivation. The cause of this hibernation in tropical species is the coming on 

 of the dry season, which produces the same physiological results as does cold 

 in the northern latitudes. I have studied the conditions of aestivation in a 

 number of species in this genus, two of which will serve to illustrate the phe- 

 nomenon as it is found in the tropical members of the genus. The conditions 

 found in undecimlineata are representative of species which Uve in the more 

 moist regions, and those of midtitcsniata of species which live on the high and 

 dry plateau, Vv^here the moisture conditions tend strongly toward aridity. The 

 proper apparatus has not been available for the accurate weighing of these 

 two species in nature, but this in no way vitiates the general results that have 

 been derived from the study of aestivation in these beetles. 



Leptinotarsa undecimlineata, like decemlineata and all the other species in 

 the genus, hibernates in the second generation of each year, no matter whether 

 the proper time is reached in the rainy season, at its close, or thereafter. 

 When the beetles are ready to hibernate they will do so, in spite of the condi- 

 tions immediately surrounding them. The second brood in this species is 

 found in general in the months of September and October, hibernation begin- 

 ning in October or November with the cessation of the rains. After emerg- 

 ing from the pupa the second generation of this beetle feeds often for as long 

 a time as three weeks or a month, but not as ravenously as does decemlineata 

 in the north. During this time the weight, both gross and dry, increases 

 steadily until the animal gradually ceases feeding. The intestine is then emp- 

 tied of all food and the malpighian tubules secrete an excessive amount of 

 waste, which is often tinged reddish in color. Then there is the reduction in 



