14 N. S. ENTOMOLOGICAL SOCIETY 



abundance of the insect from Saint John to Moncton along the 

 bay shore. Since that time the insect has increased steadily 

 and there is no possibility of the parasites gaining the upper 

 hand for several years. 



So much then, for the way in which the factors of control 

 have operated in two specific cases. 



In conclusion let us for a moment return to the table of 

 factors in control. Among these factors the insect parasites, 

 and predators occupy a somewhat peculiar position. They 

 can overtake a numerically increasing host and so have a regu- 

 lative effect not possessed by any of the other factors. Also 

 they are the only factors that can be manipulated by human 

 beings, and herein lies the possibility of preventing outbreaks 

 of certain injurious insects, such as the Fall Web worm, Forest 

 Tent Caterpillar and Spruce Budworm. 



The present outbreak of Fall Webworm in Nova Scotia, 

 for instance is clearly due to a scarcity of the two chief parasites, 

 Varichaeta and Limnerium; it might perhaps have been pre- 

 vented by introducing these insects in large numbers four or 

 five years ago from New Brunwwick, where they could have 

 been collected by the thousand. At Red Deer, Alberta, there 

 is a heavy outbreak of Forest Tent Caterpillar, that has now 

 been running for three years. Not a single parasite could be 

 found working on the larvae or pupae last year, and the same 

 condition was found by Mr. Baird to obtain this year. The 

 outbreak perhaps could have been prevented by introducing 

 about four years ago thousands of its two chief parasites, 

 Limnerium and Blepharipeza from either the Atlantic or Pacific 

 Provinces where they could then have been gathered in suitable 

 numbers. As a final illustration I will mention the oyster 

 shell scale,the only really important controlling factor of which 

 in Europe and eastern North America is a mite. Two or 

 three decades ago the scale reached British Columbia, but the 

 mite was left behind. In the Okanagan Valley the scale has 

 been steadily increasing and is now in places exceedingly abund- 

 ant; had the mite Hemisarcoptes been liberated in the Okana- 

 gan, say ten years ago, it is probable that the scale situation 

 would be considerably less acute than at the present time. 



