86 THE REPORT OF THE No. 36 



seems that the chief factor in the limitation of these pests is that the parasites are 

 apparently everywhere at the same time and that the outbreaks occur in the same 

 years almost throughout the three different regions. It looked that way to me 

 when looking at those charts just now. 



Dr. Hewitt: I do not think they quite coincide, e.g., the 1870 and 1880 

 outbreaks. 



Prof. Lochhead : Outbreaks are coincident, and the parasites must have 

 developed in the diflferent regions at the same time and in greatly increasing 

 numbers. That would seem to eliminate any method of control — for example, the 

 distribution of parasites that would tend to prevent the outbreaks. In the 

 Northern Forest Districts between those of the Central or Western at different 

 times it might be possible, if we had better resources at our hand, to carry 

 parasites from one district to the other. 



De, Bethune : I might mention one instance of very exceptional natural 

 control in connection with the American Tent Caterpillar. It was about 25 years 

 ago when at Port Hope we had a steadily increasing abundance of these insects 

 from year to year; they were extremely numerous. In this particular spring the 

 caterpillars had emerged from their cocoons when the apple buds were just opening 

 and we had a very severe frost that killed them all ; we saw no more of those 

 tent caterpillars for three or four years. Of course that would be a very excep- 

 tional case. 



Mr. Harrington : In reference to the tent caterpillar I may say that the 

 first time I was in British Columbia, that is about 1888, there was a serious 

 infestation then in the district around Victoria. Parasites were lessening the 

 ravages. That wo aid correspond apparently with the first outbreak that 

 is on that chart of the Western Region in 1888. The infestation was 

 very heavy. With regard to more recent infestations which we have had in 

 this eastern section of the country, of course three or four years ago the ravages 

 were very serious in certain districts of Quebec Province. Some species of trees, 

 poplars, etc., were almost totally defoliated for two or three years and the cater- 

 pillars were so numerous as to stop the trains. I 'know this is a fact, because 

 I was on a train which was stopped by caterpillars on the track. That infestation 

 has been checked now, and I think principally by the tachina flies as the infesta- 

 tion reached its maximum. There is no doubt, I think, that the caterpillars were 

 almost entirely wiped out by these tachinids although last year there were, of 

 course, webs to be seen m the same district. They build almost entirely on the 

 wild cherries M'hich are the natural habitat of the caterpillar under ordinary con- 

 ditions. They seldom spread to other trees until the infestation increases towards 

 the maximum, and that appears to be about every ten years, as far as my recollection 

 goes, of the occurrences which I have seen in thirty or forty years. Sometimes, of 

 course, caterpillars are subject to a fungus disease but the reduction of tlie numbers 

 I think is chiefly due to our good friends, the tachinids. 



Prof. Caesar: I wonder if Mr. Harrington has reared those tachinids. 



Mr. Harrington : I did a good many years ago. 



Prof. Caesar: The reason I ask is because I collected quite a number of 

 Forest Tent Caterpillar cocoons and reared the parasites from them, and they 

 were all Sarcophaga aldrichia, a new species described two years ago. I do not 

 mean that those Mr. Harrington saw were not tachinids, but all I reared were 

 sarcophagids. 



Mr. Gibson : We collected a large number of the cocoons and I remember 

 distinctly sending a lot to Mr. Tothill who failed to report on them. 



