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



then sown in the soil still wet with the bacterial suspension. Insects 

 were then introduced as follows: 



Compartment 1. A total of 116 striped cucumber beetles previously shown to be 

 free from wilt by feeding on cucumber plants which did not subsequently contract 

 the disease. 



Compartment 2. Miscellaneous insects (species of flies, lady bird, etc.) and angle 

 worms and wire worms. 



Compartment 3. Squash bugs. 



Compartment 4. Control, without soil inoculation or insects. 



Compartments. Nematodes (Heterodcra mdicicola). Two buckets of soil from 

 around nematode-infested tomato plants were thoroughly mixed with the soil, and in 

 addition the infested roots and stems of several tomato plants were cut up and raked 

 into the soil. 



Compartment 6. Seven wilt-free 12-spotted cucumber beetles. 



Compartments 7 and 8. Control on insects. Soil inoculated with Bacillus trachei- 

 philus, but no insects introduced. 



Until the seeds had germinated, the beetles were fed on cut stems and leaves of 

 healthy cucumber plants introduced into the compartments on pieces of heavy manila 

 paper to keep the pieces from possible contamination by the soil . 



Eight days after sowing the seed the soil was reinoculated in the same manner as 

 before with a suspension of Bacillus tracheiphilus proved virulent by needle-prick 

 inoculations into 31 potted cucumber plants, all of which wilted. 



On December 4, 1916, the young cucumber plants in all the compartments were 

 thinned out and the soil loosened. In compartment 1, 85 plants showed beetle gnaw- 

 ings on the true leaves, as did also several plants in No. 6. 



Again on December 7 the soil was inoculated with Bacillus tracheiphilus as before, 

 using great care, however, to prevent the liquid from coming in direct contact with 

 the plants. All control plants inoculated from this fluid by needle puncture wilted. 



About the middle of December, 25 striped beetles were counted feeding on the 

 plants in No. 1, and 4 more wilt-free 12-spotted beetles were added to No. 6, where 

 they were later seen feeding. 



This experiment was under almost daily observation from the time the seeds were 

 planted (November 15, 1916) until January 11, 1917, and not a single case of bacterial 

 wilt or anything suggesting it occurred during the whole time in any of the compart- 

 ments. At this date the first crop of plants was pulled, and cucumber plants grown 

 in sterile soil in pots were transplanted to the bed cage — six hills of three to four plants 

 each to every compartment. The soil was then reinoculated with Bacillus tracheiphilus 

 as before. Up to January 29 the plants were fed upon by both species of cucumber 

 beetles, but no wilt had occurred in any section of the cage. Six more small plants 

 were then set out in compartment 1, cucumber seeds planted in all the compartments, 

 and the soil reinoculated with Bacillus tracheiphilus as before. Up to February 9 no 

 wilt had appeared, although plants in Nos. 1 and 6 had been fed upon, and Diabroticas 

 were still alive in both compartments. Powdery mildew was now getting bad, so 

 all plants in the bed were pulled and fresh plants grown in sterilized soil were set in 

 each compartment. There were now six beetles in compartment 1 and one beetle in 

 compartment 6. One week later the soil was reinoculated as before and, as in each 

 preceding case, the virulence of the bacterial fluid was proved by needle-puncture 

 inoculations. At this date 6 pots of cucumber plants were placed in compartment 

 1 and 13 in compartment 6 and left for five days, at which time the leaves on every 

 plant had been gnawed by the beetles. The plants were then removed for observa- 

 tion. Three more potted plants were then placed in compartment 1, and after the 

 leaves had been gnawed these also were removed and held for observation. No wilt 

 occurred on any of these plants. 



