August, '17] BOXXQUET AND STAHL: BEET CURLY -TOP 393 



by feeding on a healthy beet for two minutes.^ In these experiments it 

 was further demonstrated that insects reared from the egg stage 

 on healthy beets were unable to produce the characteristic condition 



The curly-top leafhopper feeds on a number of species of wild 

 plants, in addition to its attacks on the sugar beet. Specimens 

 collected from wild host plants were accordingh'' tested on healthy 

 beets, but without bringing about the curly-top condition.- They 

 acquired the ability to cause the characteristic symptoms of the 

 condition by feeding on affected beets. This ability was lost in 

 from 15 to 35 days if the insects were transferred daily to healthy 

 beets. A period of incubation, dependent on temperature, and lasting 

 at least two days was required.^ 



The apparently sporadic occurrence of curly-top outbreaks in 

 remote isolated desert regions, where beets had never before been 

 grown suggested either that the leafhopper was capable of migrating 

 to great distances, or that the virulent factor resided in other food 

 plants than the beet, and was perpetuated either in a virulent form 

 or in a symbiotic relation by these plants. The first being untenable, 

 the second suggestion was investigated, the results obtained to the 

 present time apparently justifying this paper. 



Recent Investigations 



Early in the fall of 1915 it was observed that many mallow plants 

 {Malva rotundifolia) (PL 17, fig. 1) growing in the vicinity of beets 

 affected with curlj^-top showed signs of abnormal development (PI. 18, 

 fig. 1). The plants were dwarfed and the leaves were irregularly con- 

 torted, the growing bud stunted, showing onlj^ two or three extremely 

 small leaves, indicating a widespread disturbance in growth. Several 

 of these abnormal plants were examined microscopically, revealing 

 internal lesions similar to those observed in beets affected with curly- 

 top. The phloem was injured not only in the stem and roots but even 

 in the extreme parts of the leaves. The medullary rays of the stem 

 were also attacked and in some places showed total disintegration. 



1 Smith, R. E., and Boncquet, P. A. New Light on Curly-top of the Sugar Beet. 

 In Phytopathology, vol. 5, p. 103, 1915. Connection of a Bacterial Organism with 

 Cirrly-leaf of the Sugar Beet. In Phytopathology, vol. 5, p. 335, 1915. 



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

 Doctor of Philosophy at the University of Cahfornia. University Documents, 1915. 

 The Comparative Effect upon Sugar Beets of Eutettix tenella Baker from Wild. 

 Plants and from Curly-leaf Beets (with W. J. Hartung). In Phj^topathology, vol. 5, 

 p. 348, 1915. 



2 Smith, E. E., and Boncquet, P. A. New Light on Curly-top of the Sugar Beet, 

 /n Phytopathology, vol. 5, p. 103, 1915. Connection of a Bacterial Organism with 

 Curly-leaf of the Sugar Beet. In Phytopathology, vol. 5, p. 335, 1915. 



