96 



General Summaky as to Moktality 



as five days; the growth period of females as thirty-seven days and 

 their reproductive period as forty-two days ; and assuming that Per- 

 gande's percentages of males and females in the various generations 

 hold true thruout the season, a classification of the product as to stages 

 of development at the close of the season may be made as shown 

 above. 



The most interesting inferences from this computation are the 

 enormous number of offspring theoretically possible under optimum 

 conditions, the large variations in the total product due to slight differ- 

 ences in the length of the reproducing season, and the surprisingly 

 large per cent of the progeny which are still alive at the close of the 

 season. 



No account could be taken of the many mishaps which must pre- 

 vent many of the young from reaching maturity and many of the 

 adult females from producing their full quota of young; hence it is 

 not really possible that the number of young produced ever equals 

 that here shown to be possible theoretically. On the other hand, 

 these results have been worked out with mathematical accuracy from 

 averages actually secured in breeding experiments, and must serve to 

 convince any one that the San Jose scale, if allowed to multiply 

 unchecked on any favorable host plant or in any community, 

 will prove to be a very destructive pest, and they must also make it 

 clear that spraying to control it must be done so thoroly as to destroy 

 nearly or quite every living insect. 



Under the conditions which obtained in Mr. West's experiments, 

 the addition of ten days to the reproducing season would have more 

 than doubled the theoretical product. This serves to explain why the 

 scale is so much more abundant and destructive in the southern part 

 of the state than in the northern, and why it increases so much more 

 rapidly in some seasons than in others. 



