14 THE UNIVERSITY SCIENCE BULLETIN. 



The seriousness of the damage to the forage crops depends 

 of course on the number of leaf hoppers present. Not much 

 has been done to get accurate data concerning their numbers, 

 but Professor Osborn has found that frequently the numbers 

 run up far above a million per acre, and he is of the opinion 

 that in such grasses as timothy and blue grass, a million per 

 acre would not be putting the figure too high. In work on 

 the potato-leaf hopper Doctor Ball has found that in the period 

 of their greatest abundance several million leaf hoppers may 

 be found to an acre of potatoes. 



Then, as to the amount of food taken by this number of 

 leaf hoppers from the plants of that acre, and the resultant 

 depreciation in weight of the amount of hay cut, we again 

 have no definite figures because of the lack of experimentation. 

 But after years of observation, Professor Osborn gives as his 

 opinion that in some cases at least, from 25 to 50 per cent 

 of the growth of such grasses may go to feed the leaf hoppers. 



In Bulletin 248 of the Maine Agricultural Experiment 

 Station, Professor Osborn gives some idea as to the leaf-hop- 

 per damage to the hay crop of that state. In 1913 there were 

 1,194,000 acres of hay in the state, which yielded about a ton 

 of hay per acre, the value of the crop being over sixteen and 

 a half million dollars. That acreage should have produced 

 two to three times as much as it did, and if leaf hoppers are 

 responsible for even ten per cent of such shrinkage, their 

 damage becomes very serious and their control should call for 

 serious attention. Applying these figures to the hay crop of 

 the entire country, we see that at the very conservative esti- 

 mate of a ten per cent loss, the leaf hoppers reduce the hay 

 yield by at least ten million tons, valued in 1909 at about 80 

 millions of dollars and to-day at perhaps fully twice that sum. 

 Thus these insignificant little creatures become a cause for 

 real consideration, for at the very least, if the above estimates 

 be anywhere near the truth, we can safely accuse them of 

 causing an annual loss of 100 million dollars to the hay crop. 



But there is still more to this problem than the mere decrease 

 in yield. Professor Osborn, in the above-mentioned bulletin, 

 also considers the effect upon the quality of hay produced, and 

 shows that hay that has escaped the attacks of such insects is 

 of much more value than a similar amount of hay that has 



