54 THE GRAPE EOOT-WORM. 



The percentage of parasitized eggs in the field varied considerably 

 in different sections of the grape belt; as well as in parts of the same 

 vineyard. It was always highest where eggs were most numerous. 

 This was especially brought out in the different sections in the experi- 

 mental vineyards, where the sprayed areas were but slightly infested 

 with root- worms. 



Thus, Davidson's vineyard, consisting of 12 acres, located half a 

 mile north of the city, showed in 1908 the following results: 



Average 

 number of 

 Per cent eggs per 



parasitized. vine. 



Unsprayed young Concord vines 18 268. 8 



Sprayed young Concord vines 9. 5 12. 4 



Unsprayed old Concord vines 13.2 319.2 



Sprayed old Concord vines 20 23. 6 



Unsprayed Niagara vines 35 56.0 



Sprayed Niagara vines Free. 1. 2 



The Porter vineyard, located a few miles east of the town and con- 

 taining 10 acres of old Concord vines, gave the following results: 



Unsprayed plat had 14.7 per cent parasitized eggs. 

 Sprayed plat had 5.5 per cent parasitized eggs. 



By comparing the records taken during August from three different 

 vineyards located within a radius of from 2 to 3 miles east of N rth 

 East, Pa., Algren's vineyard on August 4 showed 2 per cent of para- 

 sitized eggs; Young's vineyard, August 24, showed 16 per cent; and 

 Wheeler's vineyard, August 27, 96 per cent. 



A marked increase of parasitism was observed with the advance- 

 ment of the season. The records given below, obtained by H. B. 

 Weiss, from Mr. Young's vineyard, illustrate this fact: 



Per cent. 



July 30 5 



August 13 10 



August 19 14 



August 26 - . 16 



September 2 20 



Similar records from other vineyards were not as uniform as those 

 just given, but since the percentage varies with the amount of eggs 

 present, no great uniformity can be expected unless the eggs are found 

 more or less evenly distributed in the vineyards. 



By breeding the parasites two full generations and a partial third 

 were produced. Infested eggs were obtained in the field July 13, from 

 which adults emerged August 3. These were placed with fresh eggs 

 August 4, and new adults issued August 28. The third generation 

 developing from these adults was much delayed by cold weather, but 

 at the time of concluding the field work for the season on November 

 22 the adults were about to emerge. 



