394 



JOURNAL OF ECONOMIC ENTOMOLOGY 



[Vol. 10 



Special staining methods demonstrated that organisms^ similar to 

 those previously found in affected beets were present. This striking 

 resemblance suggested the possibility of the mallow being an alternate 

 host in beet infection, and experiments were started to determine 

 the relationship. In order to verify these assumptions two different 

 methods were devised which, if successful, would furnish unques- 

 tionable proof. These methods were only the consequence of previous 

 results obtained during investigations relating to virulent and non- 

 virulent insects. 



Experiments 

 In the first set of experiments two factors were most essential for 

 success: (1) Insects must be used which were known to be non- 

 virulent; and (2) beet plants must be used which had been grown 

 under cover and were known to be healthy. Mallow plants {Malva 

 rotundijolia) which showed signs of some disturbance (PI. 18, fig. 1) 

 were selected, growing in the field which contained a large number of 

 beets affected with the characteristic curly-top. A microscopic 

 examination disclosed internal disorders similar to those previously 

 mentioned. Insects which had been kept under close ol^servation 

 for more than six months and which were known to be non-virulent 

 were selected and placed on the mallow in small leaf cages. After 

 several days these insects were removed and placed on healthy beet 

 plants in specially constructed cages, l^hese beet plants were kept 

 under close observation and the first symptoms of curly-top noted 

 (PI. 18, fig. 2). One insect was placed on an affected beet instead of a 

 mallow plant and was used as a check so that it could be ascertained 

 whether or not the condition would develop normally during the fall 

 season of the year. Table I shows the results of these experiments. 



Table I. — ^Experiments in the Placing of Non- Virulent Specimens of Eutettix tenella on Affected Mallow 

 Plants AND Their Subsequent Transference TO Healthy Beet Plants, Resulting in Curly-top Infection 



(Check on affected beet plant) 



1 Boncquet, P. A. Bacillus morulans n. sp. Thesis presented for degree of Doctor 

 of Philosophy at the University of California. University Documents, 1915. 

 The Comparative Effect upon Sugar Beets of Eulellix tenella Baker from Wild 

 Plants and From Curly-leaf Beets (with W. J. Hartung). hi Phytopathology, vol. 

 5, p. 348, 1915. 



