THE CANADIAN ENTOMOLOGIST. 87 



and the discovery in Ontario, after three or four days of a strong, steady, 

 southerly wind, of moths, such as the cotton moth, that breed only in the 

 Southern States. Winds, too, often blow young scale insects from the 

 topmost branches of one tree to those of another, or break off infested 

 twigs and leaves and scatter them throughout the orchard. It is worth 

 noting, in this connection, that the strongest and most frequent winds are 

 from the south-west. This fact, to some extent, explains the direction of 

 the spread of our worst insects. It has been observed that, if the San 

 Jose' Scale gets established in the south-west side of an orchard, it will 

 s|)read over the whole orchard much more rapidly than if it has to begin 

 at the north side and work south. 



Closely connected with the action of winds is that of rain storms. 

 These wa,sh many insects from wherever they may happen to be exposed to 

 their fury, and sweep them along, either by themselves or on whatever 

 floating material they may be able to attach themselves to, for long dis- 

 tances in the overflowing rivers and streams, to be cast up at last, still 

 alive in many cases, here and there along the shore. 



Some German entomologists, who have made observations on the 

 subject, tell us that the calm, sultry period just before a thunderstorm has 

 a peculiar effect upon insects, causing a strange, nervous sort of activity, 

 and drawing forth from their' concealment both sexes. Thev say, more- 

 over, that Aphides have been observed, during a violent thunderstorm, to 

 crawl to the crown of a plant, and, at the proper moment, launch them- 

 selves headlong into the vortex of the storm, to be whirled along possibly 

 for miles. 



But, even though these different natural means will account for a 

 gradual and continuous spread of insects, they are far from being the only 

 or even the chief means of distribution. Just as we found that the intro- 

 duction of transoceanic insects must be attributed to commerce, so ako to 

 commerce we must attribute the main part in the rapid spread of insects 

 on land. 



Of all the kinds of commerce that have been responsi!)le for the 

 carrying of insect pests from place to place, that in nursery stock has been 

 the chief in the past, before the G )vernment passed a law requiring that 

 such stock should be thoroughly fumigated and disinfected before dis- 

 tribution. It is to nursery stock that we can trace most of the rapid 



