The Bulletin. 15 



methods of spread. We will consider each of these separately, con- 

 sidering first its natural powers. 



Natural Spread. — If one of the young insects should start out as 

 soon as born and run as rapidly as it could until it became necessary 

 for it to settle down and begin to feed, it could only travel a short 

 distance, perhaps one or two rods. It is evident, therefore, that the 

 vast majority of the young insects settle on the same tree on which 

 they are born. If the trees are so set and pruned that the branches of 

 separate trees do not interlock, it will be almost impossible for 

 the young insects to get from one tree to another of their own accord, 

 and this is an important point, for the spread of the scale in thickly- 

 set orchards may be very materially lessened by keeping the branches 

 so pruned that they shall not reach from one tree to another. But 

 in spite of this, the insects will usually spread to the other trees more 

 or less rapidly by other means. 



Spread hy Wind. — Notice that we have said that the young insects 

 are very, very small ; therefore, if a wind blows through the orchard 

 during the breeding season (from April to December) the young 

 crawling insects are liable to be blown about from place to place like 

 particles of dust. Indeed, in almost every case where a large orchard 

 becomes infested it is to be noted that it spreads most rapidly in 

 the direction of the prevailing winds. Of course it is mere chance 

 whether the young insects which are thus blowoi from one tree will 

 find lodgment on another, and these winds no doubt leave many 

 thousands to die on the gTOund. But it is perfectly evident that 

 many are spread from tree to tree by this means. 



Spread hy Birds. — If a bird alights in a scale-infested tree at 

 any time during the breeding season some of the young insects may 

 crawl upon its feet or feathers and be carried off into other trees, 

 there to crawl off a^ain. There can be no doubt that thev are often 

 established on new trees in this "vvay. We have sometimes found in 

 our inspections that the portion of a tree close around an old bird's 

 nest may be thickly infested, while other parts may be slightly 

 infested or almost entirely free from the insect. In towns and vil- 

 lages we have found similar evidence, the lower branches, next to 

 the street or walk, being most frequently infested, thus indicating 

 that the English SparroAv plays an important part in its spread in 

 such places. 



Spread hy Insects. — Insects play a part in the spread of this 

 pest similar to that of the birds. Especially during the blossoming 

 season, many insects are busy going from tree to tree and are thus 

 liable to spread the young scale-insects. Even the species of Lady- 

 beetles which attack and devour the San Jose Scale have been known 

 to bear on their legs or wings the very young scale-insects. 



