April, ’20] 
BALL AND FENTON: LEAFHOPPER AND TIPBURN 
219 
ber of young that were produced on a hill was ascertained and was found 
to be about 2,000 for the second generation or about 10 million per 
acre. These results were obtained on typical fields where the average 
egg parasitism was about 40 per cent, so that the total number of 
eggs deposited per hill was above 3,000. 
Potato plants inclosed in cages that excluded the leafhoppers from 
the beginning continued to grow with green and healthy foliage until 
digging time, when all the rest of the plants in the field were dead. 
Other plants in cages in which leafhoppers were introduced developed 
the typical burning of the vines in the field, showing that the green con¬ 
dition was not an effect of the cage. Twice during the season 250 or 
more adult leafhoppers were introduced into a cage at a single time 
'with the result that all the leaves were burned and brown within three 
of four days. Plants in large cages, into which a small number of adult 
leafhoppers had been introduced, did not develop the burning until 
nymphs appeared. 
To test the relative effect of the different stages of the insect, 50 
adults of both sexes were introduced into a wire gauze cylinder on a 
potato tip, while 50 large nymphs were placed in another. In both 
cases burning developed, while the check cage remained green. In 
one test 50 males were placed in one cylinder and 50 females in another. 
The females produced serious burning while the males produced none. 
This was so striking that it was repeated with the same result. The 
males have so much less feeding capacity than the females that it is 
not safe to conclude from this single test that they are incapable of 
producing burning, but it does appear to show that they are not an 
important factor. 
In a large cage a small number of adults were introduced. In 
another an equal number of small nymphs. After two weeks no burn¬ 
ing had appeared with the adults while in the other cage here and 
there was a hopperburned leaf. In every case one or more large 
nymphs were found on the burned leaves, while there were none on the 
others. The reason why the adults produced no burning in this cage 
and did in the small cylinder was probably because in the latter they 
were confined to a small number of leaves while in the large cage they 
flew from leaf to leaf at will, while on the other hand the nymphs 
settled down on a single leaf and remained. The cylinder in which 
the 50 females had burned the tip was retained after the leafhoppers 
were released. Each day the young nymphs were removed as they 
hatched. Under this treatment new leaves were put out that remained 
green and healthy. This experiment was repeated, except that the 
nymphs were allowed to remain, with the result that the new growth 
burned in proportion to the growth of the nymphs. 
