HATCHING OF GIPSY-MOTH EGGSi . 13 



collected there had each year shown a high percentage of parasitism. 

 After the above-mentioned cold winter the parasitism was of de- 

 cidedly lower percentage, but two years later it had about reached 

 its former high point. 



In the long run it is doubtful if the cold would have any very 

 serious effect upon the general abundance of Anastatus hifasciatus. 

 Even though all the parasites as well as all the eggs above the 

 snow protection line were" killed, the proportion of parasites to 

 eggs would be the same in those egg clusters protected by the snow, 

 for there is very little difference in percentage of parasitism be- 

 tween eggs near the ground and those above 5 feet. Therefore, 

 there would be the same proportion of adult parasites to attack the 

 eggs the next summer as if all parasites and all eggs came through 

 the winter safely. 



As the result of particularly adverse conditions a decrease in 

 parasitism by Ancistatus hifasciatus, such as was evidenced at the 

 stock colony, may occur for a few years, but no doubt there is a 

 gradual recovery. 



Schedius kuvanae has received some rather severe setbacks from 

 cold winters. It hibernates as an adult, principally in leaves and 

 rubbish on the ground, and in such position it would be well pro- 

 tected from the cold if there was plenty of snow during each period 

 of extremely low temperature. Apparently such protection has not 

 been present in a number of cases, for there are records of colonies 

 from which recovery of parasites was difficult after a severely cold 

 winter. 



Some of the other imported parasites may be killed by low tem- 

 perature, but very little information has been obtained to confirm 

 this idea. 



Further investigations may throw more light upon the relationshij) 

 of low temperature to parasite mortality. 



CONCLUSIONS. 



The failure of gipsy-moth egg clusters to hatch is caused by low 

 temperature. 



An exposure of between —20° and — 25° F. is necessary to kill 

 entire clusters, though some eggs in each cluster may be killed by an 

 exposure to — 15°. No eggs will survive an exposure to lower than 

 —25°. 



When the temperature is low enough, an average of 70 per cent 

 of the clusters maj^ be killed, but this desirable condition develops 

 only in the northern part of the infested area and only during cer- 

 tain years. 



Snow will protect the Q,g^ clusters from the effects of the cold if 

 it covers them; therefore, the greater the depth of snow the larger 

 the number of clusters that will hatch the following spring. 



The benefit derived from nonhatch may vary after a cold winter 

 from 70 per cent of the clusters killed in the northern part of the 

 area to no injury to the eggs in the southern section. 



Maine and ?^ew Hampshire receive the greatest benefit from non- 

 hatch. Central and northern Massachusetts also derive considerable 

 benefit particularly in restricted localities. Connecticut, Ehode 



