BACTERIAL WILT OF CUCURBITS. 21 



SEED TRANSMISSION. 



Our earlier experiments relative to seed transmission * all gave 

 negative results. One further planting of seeds from a wilting cucum- 

 ber vine gave healthy plants which at no time showed signs of wilt. 

 Numerous plantings have also been made with cucumber seeds 

 soaked in heavy tap-water suspensions of virulent wilt bacteria 

 immediately before sowing. These tests likewise all gave negative 

 results. 



RELATION OF THE WILT BACTERIA TO CUCUMBER BEETLES. 



SUCCESSIVE INFECTIONS. 



The objection has been raised that it would be impossible for the 

 cucumber beetles to feed for several weeks in the early spring upon 

 noncucurbitaceous plants and yet infect cucurbits when they ap- 

 peared above ground. It is a well-known fact that these insects 

 are rather omnivorous and in the absence of cucurbits will feed on a 

 wide range of host plants. In a locality where cucurbits are planted 

 late in the season the beetles feed for some time on other vegetation. 

 If the wilt organism is carried only on the mouth parts or other 

 external portions of the body, one might think that after feeding 

 two or three weeks on plants not infected with cucurbit wilt none of 

 the bacteria would be left. However, early spring infection does 

 occur, and the following experiments were designed to throw further 

 light on this question. 



The small cages used in these experiments (PI. I) were covered 

 with 18-mesh wire netting, and the bases and joints were made 

 insect proof. After allowing the beetles to feed on the plants, the 

 latter, unless otherwise stated, were removed and held for observa- 

 tion in similar cages free from insects. The details of these experi- 

 ments are as follows: 



In July, 1915, at East Marion, Long Island, several striped cucumber beetles were 

 inclosed over a hill containing wilting young cucumber plants and were allowed to 

 feed on them for five days. The beetles were then removed and allowed to feed for 

 24 hours each on three healthy and uninjured young cucumber plants successively 

 caged with them. These three plants were then kept under observation in a cage 

 free from beetles, and between the seventh and tenth days all had shown evidence of 

 wilt. The cut stems showed the typical, stringy ooze, and microscopical examina- 

 tion showed the xylem elements to be full of bacteria. As no culture media were at 

 that time available, isolations were not attempted. 



No further attempts of this kind were made until the following year (Sept. 26, 1916), 

 when several striped cucumber beetles were fed for three days on plants wilted from 

 pure-culture inoculations. The diseased plants were then removed and the beetles 

 allowed to feed 5 and 15 days, respectively, on two large potted cucumber plants 

 successively introduced. The plants were afterwards kept under observation for 27 

 days, but no wilt developed in either case. 



i Rand, F. V., and Enlows, Ella M. A., 1916. Op. cit., p. 424-425. 



