VOL. XXIII. 



tanailiaii Intomologbt. 





LONDON, MAY, 1891. 



No. 5. 



SILVER-TOP IN GRASS AND THE INSECTS WHICH MAY 



PRODUCE IT,* 



BY HERBERT OSBORN, AMES, IOWA. 



The common affection of various grasses, commonly known as 

 " Silver-top,'' has received the attention of such well-known investigators 

 as Professors Corastock, Lintner, Forbes, Fletcher and others, and it is 

 not with the expectation of completely solving the problem which has 

 perplexed these careful students that I venture to present my experience, 

 but in the hope that by comparisons of experience and observation we 

 may arrive at a better knowledge of a subject at once important and 

 complex. 



The appearance *of affected grass has been often stated and can be 

 described briefly as a whitening of the upper portion of the stalk of grass, 

 especially the head, which withers without maturing seed, while the basal 

 portion is sh'-ivelled. The causes assigned for this whitening have been 

 various, but, I believe, generally referred to the injury produced by some 

 kind of insect operating at the base of the terminal node of the stalk. 



The various observations upon the insects suspected of causing the 

 injury, or found associated with it, are admirably summed up by Mr. 

 James Fletcher. Entomologist to the Dominion of Canada, in his report 

 for 1888, pp, 59-62. Briefly, the species credited with the most 

 certainty so far have been species of Meromyza, Chlorops and Thrips, 

 while Mr. Fletcher mentions suspecting species of Hemiptera, and records 

 an attempt to produce Silver-top by caging such Hemiptera (species not 

 designated) upon grass plants. 



The species which can perhaps be considered as having been most 

 positively connected with the disease is a Thrips called Limothrips 

 poaphagus by Prof. Comstock, and while, as will be shown later, I feel 

 certain that but little if any of the trouble which has come under my 



*Read before the Society for the Promotion of Agricultural Science, Indianapolis, 

 August, 1890, 



