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



Nine striped beetles were fed constantly on wilted cucumber plants from January 7 

 to February 12, 1917. On the latter date all wilted plants were removed from the 

 cage (No. XXII) and from then until March 10 they were fed on healthy young cucum- 

 ber seedlings which were so small that the leaves were entirely consumed. On March 

 10 the three beetles left alive were caged with a large potted cucumber plant grown in 

 a greenhouse free from wilt. ' Two weeks later one beetle-gnawed leaf was found 

 wilting and after three weeks nearly the whole vine was involved. Bacillus trach- 

 eiphilus was isolated from this plant and tested by successful inoculations into 

 cucumbers. The cage used for this test was covered both by wire netting and cheese 

 cloth, and had not been used for beetles since the preceding fall. 



(Cage XXIV.) From January 11 to February 5, 1917, 25 striped beetles were fed 

 on wilted cucumber plants, then all diseased plants were removed and until February 

 26 the beetles were fed on very young cucumber seedlings, which were completely 

 riddled, as in the preceding test. At the latter date a Large potted cucumber plant was 

 placed in the cage and left for three days, after which it was removed and held for 

 observation. On March 10 this plant was wilted and the vascular system was plugged 

 with the typical stringy masses of bacteria. No isolations were made from this plant; 



(Cage XVIII.) Wilted cucumber plants from pure-culture inoculations were fed 

 to three striped cucumber beetles on January 25, 29, and February 8. All wilted 

 plants were removed on February 16 and a healthy young cucumber plant was intro- 

 duced. Two days later this plant was removed and a second introduced, and so on 

 until the beetles had been allowed successively to feed on four healthy plants. On 

 February 19, plant No. 1 was starting to wilt around the beetle injuries on one leaf. 

 Six days later this plant was showing wilt on several leaves and plant No. 3 was start- 

 ing to wilt around the gnawed places on several leaves. On March 1, Nos. 1 and 3 

 were entirely wilted and No. 4 was starting; plant No. 2 showed no signs of wilt. How- 

 ever, the leaves on this plant were scarcely gnawed at all by the beetles. Isolations 

 were made from plant No. 4 on March 1 and inoculations from this source to six cucum- 

 ber plants gave typical wilt in every case. 



(Cage XVIII.) On March 20, 1917, a wilted cucumber plant was fed to the same three 

 beetles, and on March 28 it was removed and a healthy plant introduced. Two days 

 later this was removed and a second one introduced. On April 13, plant No. 1 showed 

 typical wilt, but No. 2 remained free from the disease. 



This last experiment was duplicated on the same date in two other cages (XIII and 

 XXI), but in these cases neither of the two plants contracted wilt. 



(Cage XXII.) On the same date (March 20, 1917) wilted cucumber plants from pure- 

 culture inoculations were fed to several striped cucumber beetles. On March 28 these 

 plants were removed and a healthy plant introduced. Two days later, plant No. 1 

 was removed and a second plant introduced. Both plants contracted wilt from the 

 beetle injuries and on April 13 were wilted throughout and dying. 



Plant No. 2 was allowed to remain in the cage with the beetles. On April 28 the 

 plant had long since died, but one beetle was found still alive in the cage and a healthy 

 cucumber plant was introduced. On May 7 two leaves had started to wilt next to 

 the margins, where they had been slightly gnawed. The beetle had died since the 

 last preceding observation. The wilt was a typical case, and the vascular bundles of 

 the leaf petioles were filled with bacteria. 



From the results of these " successive infection" tests it is demon- 

 strated that striped cucumber beetles are sometimes capable of 

 successively infecting three or more healthy cucumber plants after 

 one initial wilt feeding and that after one such feeding they may in 

 some cases in the active state retain their infecting power for over 

 three weeks. 



