14 



summer from 33 to 40 days. Here again with us the period seemed to be about 

 ten days or more longer. 



At Washington it was found that there were four full broods and a possible 

 partial fifth, but as the males emerged early in April, and in Ontario not until about 

 May 20th, a month or more later, we should not expect so many broods. It w^as 

 not part of my original plan to attempt to work out the life history or number of 

 broods. However, my assistant, Mr. G, J. Spencer, and I by placing a definite 

 number of the earliest larvae on each of several uninfested nursery trees secured 

 for the purpose were able to make some valuable observations. As a result of these 

 I am of the opinion that we have not more than three broods, and probably the third 

 is not quite a full one. To be absolutely certain on this point would require a good 

 deal more work with great care to see that natural outside conditions were observed. 

 Our rearing was done outside, but under cheesecloth, and in the city of St. 

 Catharines. 



Whatever the number of broods, running larvae may be seen in warm days as late 

 as November. I found a few this year on November 4th in the Niagara district. 



Estimate of the Numbek of Offspring in a Year from a Single Over- 

 wintering Female, — It is estimated that each female may on an average produce 

 400 or more offspring; approximately half of these may be males. Now if we 

 suppose, as I think is correct, that we have not more than three generations, the 

 total number of offspring at this rate from a single adult, if all lived, would be 

 16,000,000, and if we estimate the number of generations at two and one-half it 

 would be 8,000,000, If we allow for a total mortality of 50 per cent, in each 

 generation we shall still have at least 2,000,000 if there are three full broods, and 

 1,000,000 if there are only two and a half. It is because of this marvellous power 

 of reproduction that the San Jose Scale, though such a tiny creature, is so 

 destructive. None of our other species of native scales can increase at anything like 

 this rate, the highest probably being not faster than an average of 1,000 from a 

 single female in a season. 



MEANS of distribution. 



By far the most important of all the various means of distribution of the 

 San Jose Scale from one district to another has been infested nursery stock. 

 In this way it has been carried from California to the Eastern States, Canada, and 

 to several other portions of the world. Once in a locality, it spreads from tree to 

 tree and orchard to orchard by the little active larvae crawling upon various kinds 

 of insects or birds that alight upon or frequent infested trees and then go to some 

 other tree either near by or at considerable distance. As active larvae abound on 

 infested trees from the end of June to the severe frosts, it is quite evident that they 

 are also carried on the hands, clothes, baskets or ladders of the pickers, or even on 

 the horses or vehicles used in the orchard gathering the fruit or for any other pur- 

 pose. Where trees are close together the larvae travel from branch to branch, or 

 may be carried by the wind a short distance from a higher branch of one tree to a 

 lower one of the neighboring tree. Many of the inspectors of nursery stock believe 

 that the wind plays an important part in infesting stock situated near large, badly 

 attacked trees. Just how far the scale may be carried in this way I cannot say 

 definitely. In a moderate breeze I have caught them on tanglefoot placed near 

 the ground six feet away from a branch about 15 feet high. I should not be at 

 all astonished if strong gales would carry them occasionally as far as 30 or 40 



