Ecological and Behavior Notes 55 



about one inch high. On these, about thirty adult beetles 

 were found feeding, one pair in copulo. They had prob- 

 ably just emerged from the ground. On April 15, the 

 popuhition of adult beetles seemed to be at its height, 

 and egg-laying was prolific. No larvae were on the leaves, 

 and by digging in the soil under the plants we unearthed 

 no pupae. Hence at this date we got the eggs produced 

 by the first generation. On April 25, the adults had 

 nearly all disappeared, and eggs were rare, but thou- 

 sands of small and medium-sized larvae were defoliating 

 the plants. By May 13, no eggs, no larvae and no adults 

 were to be seen, but an inch or so beneath the surface of 

 the soil were found hundreds of pupae. A hundred of 

 these were removed from the earth under one plant. 

 They were taken into the larboratory, and on May 16 the 

 yellow pupae transformed into blue beetles. On May 15, 

 just the day before the insects in the laboratory matured, 

 the field was examined and only one adult beetle could 

 be seen. The date of emergence of the population must 

 have been determined by its controlling factors with 

 most wonderful precision, for on May 16, at 3 p. m., enor- 

 mous numbers of fresh adults were at work on the dock. 

 None were yet copulating or ovipositing, nor were any 

 females with distended bodies in evidence. They all 

 looked alike in regard to size, and I could not tell at a 

 glance if all were males (due to priority of male emerg- 

 ence), or if the females had not yet had time to become 

 distended. In the ground beneath, yellow pupae were 

 scarce. 



The field could not be visited for a month. On June 

 27, we found the blue adults abundant once more. The 

 many dock plants were almost defoliated. I have ob- 

 served this field for a number of years, but this was the 

 first year that the beetles had wrought such destruction. 

 Plate V, figure 3 shows a dock plant— the upright mid- 

 ribs—all that was left of a thriving clump. This was a 

 typical plant from the field, and not at all a selected 



