PEDIGREE BREEDING. 275 



and 10 female. I allowed these to breed freely as before, and obtained in the 

 fourth generation, L. decemlineata, So male and 106 female; L. pallida, 190 

 male and 210 female. 



I then transferred the entire lot to nature in a situation where I could keep 

 control of them. 



In the fifth generation I gathered all the adults and found : L. decemline- 

 ata, 211 male and 209 female; L. pallida, 509 male and 540 female. 



It was evident that pallida was more than holding its own in this experi- 

 ment. All were subsequently returned to the plot where the experiment 

 was being conducted to hibernate. The following winter was a hard one, 

 and the plot where the beetles were was frequently subjected to freezing and 

 thawing conditions most unfavorable to hibernation. In the spring there 

 emerged, L. decemlineata, 6 male and 10 female; L. pallida, 14 male and 15 

 female. These I allowed to breed together upon a plot of potatoes supplied 

 for the purpose, and counted in the sixth generation, L. decemlineata, 314 

 male and 301 female; L. pallida, 819 male and 761 female. It is clear that 

 pallida was becoming well adapted to the condition of its environment. I 

 felt that further experiment with this form unconfined in nature was neither 

 safe nor desirable, and exterminated the entire lot in the sixth generation. 

 It would have been of great interest to have allowed this experiment to go on 

 and to have given the insects freedom to spread over the country, to see how 

 fast and how far they would have gone, but the nature of the species, its huge 

 capacity for food, and the plants attacked unfortunately made such an experi- 

 ment entirely out of the question. 



At the beginning of these experiments with pallida a single male pallida 

 was crossed with 4 females of decemlineata, giving the first hybrid generation 

 with the decemlineata character dominant. From these beetles I selected 

 lots of 10 males and 10 females, and got offspring as follows: (A) L. pallida, 

 21 males and 10 females = R; (B) L. decemlineata, 58 male and 51 female = 

 D + 2 Dr. 



These lots w : ere now reared in succeeding generations. 



Lot A. These hibernated, and there emerged of pallida 3 males and 2 

 females, which were bred, and gave a fourth generation which consisted of 

 L. pallida, 21 male and 10 female, without traces of intermediate or decem- 

 lineata characters. These were bred for the fifth generation, giving of L. 

 pallida 41 male and 40 female. This generation hibernated, and thereafter 

 emerged and were bred in cultures, giving in the sixth generation of L. pal- 

 lida 82 male and 61 female, with no trace of decemlineata. This series 

 was in the seventh generation exterminated by an accident in late larval and 

 pupal stages. It is evident, however, that the material of lot A was either 

 pure pallida or that pallida was dominant to the extent of submerging and 

 keeping submerged any decemlineata characters. 



