41 8 Journal of Agricultural Research voi. vi, no. n 



they were allowed to feed for 1 1 days. Observation after two weeks showed unmis- 

 takable signs of incipient wilt around some of the beetle injuries on the leaves — that is, 

 a lighter dull green and slight flaccidity of the tissues. With the expectation that 

 the wilt would extend throughout the leaves the pouring of plates was deferred. 

 However, these incipient infection areas dried up without spreading further, and 

 consequently it was impossible to obtain cultures. That B. tracheiphilus was present 

 in the wilted vines fed to these beetles was shown by the subsequent inoculation of 

 cucumbers, cantaloupes, and squashes with cultures obtained from these wilted 

 vines (strains R230 and R235). Numerous inoculations with these two strains have 

 shown them to be virulent upon cucumbers and cantaloupes, but inoculations on 

 several varieties of squash have given nothing more than incipient infection. 



Experiment 2. — On October 25, 19 15, striped cucumber beetles were collected at 

 Giesboro Point, D. C, in a squash field where bacterial wilt was very prevalent. 

 These beetles were fed for three days on plants which were wilting as a result of inocu- 

 lation with pure cultures of B. tracheiphilus. They were then placed in small boxes 

 provided with screened covers, and held in the ice compartment of a refrigerator at a 

 temperatiu-e of about 10° C. for five weeks and four days. At the end of this time 

 (Dec. 6) the beetles were removed and placed in cages containing young cucumber 

 plants. Four to six beetles were placed in each of the six cages used, each cage con- 

 taining three young plants. After being allowed to feed on these plants for 10 days 

 the beetles were removed and the plants kept in one of the Department greenhouses 

 where there had been no cucurbit wilt since the preceding spring and where no cucur- 

 bitaceous insects were present. 



On December 17 leaves injured by the beetles on three of these plants were wilted. 

 Microscopic examination showed bacteria present in great number in the vessels of the 

 petioles, and poiired plates from the wilted leaves and petioles gave pure cultures of 

 the wilt organism (strain R313). Needle-prick inoculations from these cultures again 

 gave typical wilt on cucumber plants. On December 24 a gnawed leaf on a fourth 

 plant was found wilting, and was removed from the plant. Enormous numbers of 

 bacteria were present in the vascular tissues, and cultures (strains R31S and Eni26) 

 isolated therefrom gave also successful infection when pricked into the leaves of 

 young cucumber plants. From the portion of petiole remaining the wilt gradually 

 extended throughout the plant, which finally collapsed. On January 4 another 

 plant was found entirely wilted. The gnawed leaf which had wilted first, and from 

 which the wilt had spread throughout the plant, was photographed and preserved. 

 Cultures (strain Eni24) and paraffin sections (En36) were made from the petiole of 

 this leaf. The organism isolated gave typical infections when inoculated into cucum- 

 ber plants. 



Experiment 3. — Another lot of D. vittata collected in the squash field referred to 

 in experiment 2 was fed for three days on old wilting stems of squash (C. maxima) col- 

 lected in the same field. After keeping these beetles in storage for two months under 

 the same conditions as in experiment 2, they were removed and caged for five days 

 with 12 young cucumber plants. Although these plants were under observation for 

 over two months no wilt appeared in any of them. 



Experiment 4. — On December 16, 1915, five specimens of D. vittata and four of 

 D. duodecimpunctata hibernating under natural conditions in the squash field at 

 Giesboro Point, D. C, were sifted from the siu-face soil and taken to the greenhouse. 

 The striped and spotted beetles were placed at once in separate cages, each containing 

 three young cucumber plants. Although the beetles fed freely on these plants, the 

 results of this experiment were negative. 



The negative results in experiment 3 possibly may be explained by 

 the fact that the wilted plants fed to the beetles were old, ripe squash 



