188 



from drought, or if it is a wet season they claim they are dyiug 

 from ^\et weather. We have demoustrated conclusively, 1 tliink, 

 that insect troiihh's (h» not (h'pend on drought. In lact, the 

 most destructive insects worlv better under moist conditions. 

 So far as the relative abundance now and formerly is concerned, 

 it is the habit of all destructive insects to be very destructive for 

 a series of years and then practically disappear. This is, under 

 natural conditions they go in waves. There is no particular 

 period, but wlu^never the conditions, whatever the}' may be, are 

 favorable for their rapid increase, aiid their enemies are not 

 present in mimbers, they start another invasion and sometimes 

 kill off nearly all their host trees. The most striking example 

 of the ctmiplete extermination of an insect throughout a vast 

 area was in 1893. In 18U1 and 1892 the pine throughout West 

 Virginia and Virginia was dying at an enormous rate. We 

 found that it was being killed by the southern pine beetk', which 

 was threatening the total destruction of all the timber in those 

 two States, and did kill from seventy-live to eighty per cent, of 

 the best merchantable timber. In the winter of 189o, in January, 

 it was twenty-five degrees below zero in many sections in this 

 area. The next spring when we went into the woods to continue 

 our investigations, we found all of the broods of this beetle dead, 

 and as we continued the investigation we found them dead all 

 over the area. Since that time to the present, there has not been 

 a single specimen of that beetle found in the area mentioned. 

 This is an example of climatic infiuence. If we could have some- 

 thing of that character come along and clean out the chestnut 

 blight, it would settle all this trouble; but we can not depend 

 on such things to happen. This killing of the southern pine 

 beetle by cold was due to the fact that it is a southern insect 

 which had worked its way northward during mild seasons, so 

 that when the extreme cold came it was exterminated. This 

 cold did not kill any of the local insects tliat were working in 

 the bark with it. The same insect is now threatening the de- 

 struction of the timber throughout the southern States. Our 

 work in the south during the past ^summer has led to the exten- 

 sive cutting of infested trees by the owners in carrying out our 

 recommendations, and I think the beetle will be controlled. 



