420 Journal of Agricultural Research Voi. vi, no. n 



In each of eight direct summer field tests, one to five striped cucumber 

 beetles were fed for one to three days on wilting cucumber leaves and 

 petioles and then at once caged up with several healthy young cucumber 

 plants. In six out of these eight tests bacterial wilt appeared in one to 

 two weeks and only on plants gnawed by the beetles. 



In the two fields (East Marion, Long Island, N. Y.) where spray tests 

 were carried out during the season of 191 5 the prevalence of bacterial wilt 

 closely followed that of the striped cucumber beetle. Throughout the 

 season careful and frequent observation failed to disclose a single case of 

 wilt which had not evidently started in a part of the plant injured by 

 cucumber beetles (PI. LUI). In these two fields no wilt had appeared 

 up to the ist of July. A few cases were observed on July 3, while 

 the greatest number of cases was found during the last 10 days of the 

 month. Practically no new cases of wilt appeared after the 30th of 

 July. The first striped cucumber beetles of the season were seen from 

 June 15 to 17. In field i the first beetles were found on June 17 between 

 cages 14 and 15.^ On July 3 there were only seven cases of wilt in the 

 whole field, and six of these occurred near or about where these beetles 

 had been collected. The beetles were most numerous between June 24 

 and July 8, in fact so numerous that in order to save the plants from 

 entire destruction an application of a proprietary dust insecticide (con- 

 taining lime, Paris green, etc.) was made upon the unsprayed plots. 

 Thus, for a few days, or until new growth appeared on the vines, there 

 were no untreated cucumber plants in these two fields upon which the 

 beetles could feed. From this date on, the beetles began to disappear 

 from these fields. In the variety-test block and commercial fields in 

 the vicinity the plants were younger and for the most part were untreated. 

 In fact, most commercial plantings were just breaking through the 

 ground on July 10. Such fields present an attractive feeding ground for 

 the beetles. In the two experimental fields there were only a few beetles 

 present on July 15, and they were exceedingly scarce after July 30. 



When it is remembered that under field conditions usually one to three 

 weeks elapse between time of infection and the appearance of wilting in 

 the plants, it will be seen that the rise and fall in the number of plants 

 with bacterial wilt closely follows the rise and fall in the number of beetles 



(fig. I). 



The two fields just discussed had been planted to cucumbers the pre- 

 ceding season. About a quarter of a mile from field i a cucurbit variety 

 test block was located. This land had not been plowed for several years. 

 Although separated only by slightly rolling, plowed land from field i, 

 where striped cucumber beetles appeared on June 17, no beetles appeared 

 here until about the end of the first week in July. This was just after 



* These beetles were used in the cage transmission tests recorded in a former paper (Rand, F. V., op. cit.) 

 and mentioned in a preceding paragraph. 



