371 



being made in such a way that it does not dry. I presnme it comes nearest to our 

 printer's roller glue. The caterpillars never pass above it from below. Coming down 

 the tree they jump over it. The devices for putting it on are very simple. That is 

 the method which experience has shown to be the most satisfactory there; but it is a 

 preventive method and chiefly to be considered when you have given up the fight 

 for extermination. 



The main thing for you to do is to try to stamp it out during the active season and 

 use all your energies to that end. The arsenicals are not expensive, and if an analy- 

 sis is made of the Paris green, or whatever form of arsenic is used, to insure its purity, 

 I can see no reason why the whole area should not be practically cleared off during a 

 single season. That should be carefully followed up by close observation, with a 

 view of repeating it in the case of some omitted center or point where they may be 

 found in a subsequent year. In case they have not gone into the woods it seems to 

 me feasible to exterminate them. 



I would make one other suggestion, and that is, that as an auxiliary method it 

 would be well to spend |1500 or $600 in sending one or two persons abroad next 

 summer with no other object tlian to go to some section of northern Eurojje to collect 

 and transmit to authorized persons here a certain number of the primary parasites of 

 this species, which are known to check its ravages over there. The insect was un- 

 doubtedly brought over by Trouvelot without any of its natural checks. In my 

 judgment it would be well worth trying to import its parasites from abroad. The 

 advantage would be this : If you failed to exterminate it by spraying, its parasites, 

 seeking for this particular host, would be more apt to find the overlooked or escaped 

 specimens than man would. 



Professor Fern.vld. Do you think that any of our native parasites will be liable to 

 attack this insect? 



Professor Riley, Experience justifies the belief that some of them may, in time. 



Professor Fernalx). Have we a case on record ? 



Professor Eiley. Yes; though they are not numerous. Pieris rapw or the Imported 

 Cabbage-worm has some native parasites. There are other cases, but I should have 

 to consult ray notes.* 



Professor Fernald. In reply to the question which was first asked as to whether 

 it is possible to eradicate the insect at all, let me suppose a case. Suppose we have a 

 tree like the elm I see yonder, and suppose we know it to be the only tree in America 

 that is infested. I think you will all agree with me that for a small sum of money the 

 thing could be eradicated. Suppose there were two — suppose all the trees on the 

 common were infested. If they could be eradicated from all those trees it is only a 

 question of time and money to eradicate them from over a much larger territory. It 

 is a question of time and intelligent labor ; I say intelligent advisedly. Right here I 

 would suggest very earnestly that the committee or commission should have a scien- 

 tific man upon it. This is the advice I gave, with all the force I could, to the former 

 commission, for the reason that there are a thousand and one things constantly com- 

 ing up, where it is necessary for some to know and be able to answer questions. 



As to the question of territory, I only raised that to know how it had been deter- 

 mined. It is possible it is not so extensive as indicated ; but it may be. 



Professor Shaler. I thought it best to put it at the highest figure. My own 

 opinion is that we shall not have to deal with an actual area of more than 9 or 10 

 square miles. 



Professor Riley. Is it not true that so far you have found this pest chiefly on or- 

 chard trees? 



Professor Shaler. On orchard trees and elms. 



Professer Riley. That is unfortunate, because it increases the difficulty of treat- 

 ment. 



"Several native species attark Scolytus rugulosus. Tlie same is true of the Hop Aphid (Phorodon 

 \urmdi) and of several imported species of Bark Lice. 



