174 



PAEASITES OF GIPSY AND BROWN-TAIL MOTHS. 



Table VIII. — Average percentage of parasitism of gipsy-moth egg masses at different 

 distances from center of colony. 



Distance from center. 



Number 

 of egg 

 masses 



collected. 



Percent- 

 age of par- 

 asitism. 



Distance from center. 



Number 

 of egg 

 masses 



collected. 



Percent- 

 age of par- 

 asitism. 



At center 



20 

 66 

 78 

 80 

 60 

 100 

 85 



29.26 

 24.68 

 21.75 

 14.43 

 8.61 

 3.59 

 3.44 



350 feet 



50 

 70 

 60 

 70 

 70 

 70 



0.41 



50 feet 



400 feet 



.18 



100 feet 



450 feet 



.055 



150 feet 



500 feet . 



.42 



200 feet... 



550 feet 



.00 



250 feet 



600 feet 



.00 



300 feet : . . . 











When in the fall of 1909 it had become rather certain that the rate 

 of dispersion of Anastatus was only going to be about 200 feet per 

 year, plans for colonization along very different lines in 1910 were 

 immediately put into execution. In four of the five colonies all of 

 the egg masses which could be easily secured were collected and 

 brought to the laboratory, where the eggs were separated from their 

 hairy covering. This is best effected by gently rubbing them over 

 a piece of cheesecloth stretched on a frame. (PI. XX, fig. 2.) 

 The hairs pass through and the eggs are left. 



The number of parasitized eggs present was then estimated, and 

 found to be very close to 90,000. In the spring, after all of the healthy 

 eggs had hatched, those remaining, including all which were para- 

 sitized, were divided into 100 lots, each of which was supposed to con- 

 tain approximately 900 parasite larvae. An equal number of small, 

 wire-screen cages was prepared (PL XII, fig. 1), and about the middle 

 of June, when the male parasites began to issue, and when it was 

 becoming possible to determine with some degree of assurance just 

 where there were likely to be large numbers of gipsy-moth eggs a 

 little later, the work of placing these cages in the open was begun. 

 (See also PI. XII, fig. 2, showing front and bottom of cage prepared for 

 use in Anastatus colonization in 1911.) They were finally placed, each 

 in a separate locality, and each, so far as has been determined by sub- 

 sequent investigation, in localities where the parasites had an excel- 

 lent opportunity to work to the best advantage as soon as they issued. 

 Not all of these colonies have since been visited, and probably some of 

 them never will be seen again, but all that have been examined have 

 been found in the best of condition. 



Early in the fall of 1910 the dispersion studies of 1909 were repeated, 

 with results which have already been indicated in Mr. Wooldridge's 

 diagram, and the egg collections were also repeated for the purpose 

 of securing material for additional colonization work in 1911. With 

 little difficulty some 270,000 parasitized eggs have been secured, and 

 were it not for the fact that the proper care in placing the number of 

 colonies thus provided for will probably tax all available resources 



