64 THE GKAPE ROOT-WOEM. 



the beneficial effects of poison sprays are due rather to a distaste on 

 the part of the beetles for poisoned foliage, and their consequent 

 abandonment of sprayed foliage and migration to unsprayed areas, 

 than to the direct killing effect of the poison. This view is supported 

 to some extent by cage experiments which showed that in many 

 cases when confined in cages the beetles fed but slightly upon sprayed 

 foliage and the death rate was not as rapid as might be wished. In 

 addition to this, beetles thus confined with poisoned vines have in 

 feeding indicated a preference for unsprayed areas, all of which left 

 reasonable cause for doubt as to the direct efficiency of arsenicals as 

 a killing agent. 



During our investigation of this pest, covering the seasons of 1907, 



1908, and 1909^ we have observed this tendency of the beetles to feed 

 more freely upon the unpoisoned than upon poisoned foliage, both 

 in the open vineyard and in cages, yet we have no direct evidence of 

 wholesale migration of the beetles from sprayed areas. 



CAGE EXPERIMENTS WITH POISON SPRAYS AGAINST THE 



BEETLES. 



On July 13, 1907, 100 beetles recently emerged from the soil were 

 divided into two lots of 50 each and placed in cages; one cage con- 

 tained sprayed foliage collected from a vineyard recently sprayed, the 

 other unsprayed foliage. The beetles in the cage containing the 

 unsprayed foliage fed freely upon the leaves soon after they were 

 placed in the cage, whereas those placed in the cage containing the 

 sprayed foliage did but little feeding during the first 3 days. During 

 the next 3 days there was evidence of an increased amount of feeding. 

 At the end of the 6 days, 25 of the beetles feeding on the sprayed 

 foliage had died as against 6 dead beetles out of the 50 feeding on the 

 unsprayed foliage. At this date (July 19) the experiment terminated 

 on account of the withering of the sprayed foliage, and the impossi- 

 bility of obtainmg additional recently sprayed foliage. 



Another cage experiment to observe the feeding of beetles upon 

 poisoned and unpoisoned foliage was undertaken during the summer of 



1909. This experiment was made upon young grapevines growing in 

 large flower pots and covered with a wire screen (see fig. 22). Thus 

 the freshness of foliage was assured throughout the experiment and 

 the limited area of the plant permitted close observation of what took 

 place. Three plants growing in pots were used in this experiment. 

 The plants in two of the pots were sprayed very thoroughly, care being 

 taken to cover the entire upper surface of all of the leaves with a poi- 

 soned spray, which consisted of Bordeaux mixture with 3 pounds 

 arsenate of lead to 50 gallons of the mixture, the proportions used in 

 field experiments. The plant in the third pot was unsprayed. An 



