81 



Pot No. 1 was examined again, July 26, sufficiently to show that 

 the corn roots were being injured, and that at least two root-worms 

 were present. One of these was free in the soil, probably preparing 

 to pupate, and the other, half an inch long or virtually full-grown, 

 had eaten into the base of the stalk just above the origin of the roots, 

 so injuring the plant that it had begun to wither. 



Both pots were inspected daily until August 7, when an adult 

 Diabrotica longicornis appeared during the afternoon on a corn plant 

 in Pot No. 2. At an examination made during the forenoon this beetle 

 had not been seen. August 8 the earth in Pot No. 2 was dug up on one 

 side to a depth of a little more than an inch, and ten corn root-worms 

 were found therein, together with a pupa which was a little more than 

 an inch below the surface. Nine of the larvae were out in the dirt, as 

 is usual when they are about to pupate ; the other was feeding on a 

 grain of corn which had failed to sprout. August 16, a corn root-worm 

 about 7 mm. long was seen crawhng over the ground in Pot No. 2. 

 A partial examination of the earth in this pot disclosed one adult larva 

 and two pupae within an inch of the surface. On the 20th of August 

 a pupa and a dead adult were found in Pot No. 1, and on the 21st an- 

 other adult beetle, not yet fully colored, was seen in No. 2. On the 24th 

 of August an adult emerged in Pot No. 1. The earth was now 

 searched to a depth of several inches, but only two larvae were found. 

 September 21, both pots were thoroly searched, with no additional 

 result, and the experiment was closed. 



There were thus found in these cages 16 larvae and two pupae, 

 from which five adults were derived, the dates of emergence ranging 

 from August 7 to August 28 — 344 days and 365 days respectively 

 from the beginning of the experiment. It will be seen that there was 

 no evidence of the possible occurrence of more than a single gener- 

 ation in a year. 



Experiment 2848. On the 27th of April, 1906, my field assistant 

 in Ford county shipped to the office at Urbana a quantity of soil ob- 

 tained from a corn field in which he had found Diabrotica eggs ; and 

 in this soil, placed in large pots, two grains of corn were planted for 

 each pot, a single plant being left as a food supply to any possible 

 root-worms that might hatch from eggs which had been deposited the 

 preceding fall. 



Examinations were made at irregular intervals from May 10 to 

 the 14th of June, at which latter date there were found, in eight of 

 the pots, twelve Diabrotica larvae of the following lengths: 1, 1.4 mm.; 

 1, 1.7 mm. ; 1, 2 mm. ; 3, 3 mm. ; 1, 5 mm. ; 1, 6 mm ; 2, 7 mm. ; and 2, 



