Potato Mosaic. 175 



COLORADO POTATO BEETLES. 



A similar test was made with larvae of Colorado potato 

 beetles (Leptinotarsa decemlineata Say.), commonly called potato 

 bugs. A hundred or more actively growing individuals were 

 transferred from mosaic plants immediately to each of 10 healthy 

 plants where they did more damage than is usually permitted by 

 potato growers. However, the plants remained free from mosaic 

 until dug. Checks, consisting of 5 untreated plants in the same 

 cages as the 10 treated ones and of 9 plants grown in 3 other 

 cages and fed similarly with beetles from nearly mosaic-free 

 potato plots, also remained healthy. 



OTHER INSECTS. 



It is quite probable that sucking insects other than aphids 

 contribute to the spread of mosaic. Such insects, including leaf 

 hoppers and plant bugs, feed upon potato plants. 1 A beet disease 

 apparently somewhat similar to potato mosaic ' is transmitted by 

 beet leaf hoppers (Eiitettix tenella Baker) 15 . Aphids often ap- 

 pear to be more abundant than other types of sucking insects; 

 but are smaller individuals than some types and may be less prev- 

 alent in some places and seasons. However, all seem to fequire 

 similar control measures, regarding mosaic or otherwise, al- 

 though much study could be done profitably upon the relations 

 between mosaic and the various potato insects. • ■ 



Other Possible Factors in the Spread of Mosaic. 



the seed-cutting knife. 



The same knife was used, in 1919, to cut a mixture of 

 mosaic and healthy stocks of tubers, to test whether the knife 

 would carry enough juice from a diseased tuber to a healthy 

 one to transmit the disease. First a tuber from an all-mosaic 

 stock was cut, then one from a rogued stock, and so on. Each 



15 Ball, E. D. The beet leafhopper and the curly-leaf disease that it 

 transmits. Utah Agri. Exper. Sta. Bui. 155. 56 p. 5 figs. 5 pi. 1917. 



Shaw, H. B. The curly-top of beets U. S. Dept Agri. Bur. Plant 

 Indus. Bui. 181. 46 p. 9 figs. 9 pi. 1910. 



