August, '22] FENTON & ressler: artificial production of hopperburn 293 



must have contained a toxic principle. Inoculation of check leaves 

 with water blanks failed to produce injury. 



Inoculation of Potato Leaves by Needle Punctures 



On July 27, 80 nymphs in advanced stages were macerated in a small 

 quantity of water. Small drops of this solution were placed on the under 

 surface of the leaves and then using a very fine needle, the leaves were 

 punctured 25 times. This procedure was repeated July 28, 29 and 30. 

 July 31 one leaf so treated showed a slight burning at the tip but the 

 others were normal. August 2 all leaves so treated but one showed 

 a slight curling. August 10 this experiment was closed, there being 

 no sign of hopperburn on any of the leaves, although there was a large 

 scar at the point of inoculation. 



Inoculation by Means of Crushing the Nymph on a Leaf Abrasion 



• Having failed to get positive results in the above tests, it was 

 decided to crush the live insects on the leaf, making in so doing a cut 

 in the leaf surface. Three fifth instar mmphs were crushed near a large 

 side vein of one leaf; one each day, on July 27, 28 and 29, respectively. 

 At each point of inoculation the tissue turned yellow and then brown, 

 but the injury was very localized and the rest of the leaf re-mained 

 perfectly normal. A second leaf received the same treatment except 

 that on the first day a fourth instar nymph was used and the results; 

 were the same. Thirteen nymphs in various stages were crushed on 

 a third leaf during a three day period and in this experiment the injury 

 was much more noticeable. Not only did the tissue immediately 

 beneath the crushed nymph turn brown but also the area surrounding 

 it was affected in the same way. This was proof that the nymphs 

 contain a toxic substance but in sm.all quantities. 



Inoculation of Potato Leaves by Leafhopper Residue 



On July 29 the residue left over from 58 crushed adults in the needle 

 inoculation experiments mentioned above was placed on potato leaves 

 and leaf petioles and pricked in with a fine scalpel. Twenty-four hours 

 later the tissue beneath had whitened and there was a decided lesion. 

 However, the injury continued to remain localized and the leaves were 

 apparently little affected by this except in one case. Here the lesion 

 on the petiole was so pronounced that it was nearly girdled. This 

 experiment demonstrated that the adults apparently possess the same 

 toxic substance as the ny.mphs and further it partially explained the 

 lack of better results in other inoculation tests; namely, that the mere 



