4 BULLETIN 828, U. S. DEPARTMENT OF AGRICULTURE. 



The truth of this statement is seen at once when one thinks of the 

 large numbers of beetles often present in a field during their maximum 

 prevalence. If any considerable proportion were carriers of wilt not 

 a single plant could escape infection at some time during the season. 



WELT CURVES VERSUS BEETLE CURVES. 



In a preceding publication x by the writers a discussion was given of 

 the records of striped-beetle prevalence versus wilt prevalence (1915) 

 in three experimental fields at East Marion, Long Island (fig. 1, 

 Fields I, II, and III). The graphs here reproduced (fig. 2) show that 

 a definite relation existed between rise and fall in beetle and wilt 

 curves under two sets of conditions in which the beetles, appearing at 

 widely different dates, were the variable environmental factor. No 



isian d 



Fig. 1. — Map of northeastern Long Island, showing location of experimental fields I to IV and of wilt 

 sequence records in fields I to XVI. The arabic numerals show the sequence of wilt appearance during 

 the spring of 1913. (Map drawn by Wayland C. Brown, formerly of the Bureau of Plant Industry.) 



direct relation to meteorological conditions could be found. In all 

 three fields about one month intervened between the maximum 

 prevalence of striped cucumber beetles and of bacterial wilt. 



The wilt records of 1915 were made by counting at each date of 

 observation all living cucumber plants infected with wilt and includ- 

 ing not only all new cases but also any wilted plants that might have 

 lived over from the time of the previous count. It was thought pos- 

 sible that by this method some cases might have been counted more 

 than once, thus moving the maximum of the wilt curve forward too 

 far. Therefore, during the following season (1916) in the same 

 locality much more careful records were kept of both beetle and wilt 

 prevalence in Fields II and Ila (figs. 1 and 3). At each date of beetle 

 observation an area one-tenth the size of the whole field was measured 

 off, and so far as possible all striped cucumber beetles in this area were 



1 Rand, F. V., and Enlows, Ella M. A., 1916. Op. cit., p. 420-423. 



