12 BULLETIX 1080, U. S. DEPART.AIEXT OF AGRICULTURE. 



show that unless some change takes place, such as removing the 

 debris or increasing it hj brush from cutting, the proportion of 

 those above and below the 5-foot line will remain approximately the 

 same. Having determined TO per cent as being the average propor- 

 tion of egg clusters laid above 5 feet, we can see just how valuable 

 as a means of control nonhatch may be where the cold is sufficiently 

 severe to kill all unprotected clusters. 



This particularly desirable state of affairs can not be looked for 

 in a large part of the territory, for the temperature does not go 

 low enough. The " point " notes show all variations between the 

 above-mentioned percentage and no killing at all. Occasionally 

 there is a mild winter with no low temperature and all eggs hatch 

 the following spring. 



As nonhatch is caused by a temperature of from —20° to —25° 

 F. we can only expect to find it in territory subjected to such l^w 

 degrees. Temperature records obtained from the 50 stations of 

 the Weather Bureau which are located in the present area of in- 

 festation show that any prophecy as to just what would happen 

 . in any locality would be quite useless. If the law of averages may 

 be considered in this case, killing cold will occur in a majority of 

 years in all of Maine and Xew Hampshire except a narrow area 

 along the coast. In Massachusetts such cold, at least as reported by 

 the weather stations, is the exception, but there appears to be a 

 greater tendency toward it in Worcester County and the northern 

 part of Middlesex County. The remainder of the infested area, 

 with the exception of the northern part of Windham County in 

 Connecticut from which extreme low temperatures are occasionally 

 reported, apparently escapes cold severe enough to kill the eggs. 



These general conclusions, based as they are upon Weather Bureau 

 records, apply to the sections as a whole. Local conditions, how- 

 ever, vary to such an extent that we may find nonhatch in restricted 

 areas in sections from which temperature records would apparently 

 exclude it. " Observation point " investigations prove this to be 

 particularly true of northern and central Massachusetts. 



It is possible that nonhatch is responsible for the slow increase of 

 the gips}" moth in many localities where food conditions would seem 

 to point to just the reverse. 



EFFECTS OF COLD ON PARASITES. 



There is reason to suppose that a drop in temperature low enough 

 to kill the eggs will have some effect upon the imported parasites, 

 particularly those which attack the eggs themselves. Two egg para- 

 sites, namely, Anastatus hifa^sciatus Fonsc. and Schedius kuvanae 

 How., have become well established in Xew England. The former 

 passes the winter as a full-grown larva within the egg of the host. 

 ^0 collections of eggs parasitized by Anastatics Mfasciatus have 

 been made after extremely cold weather for the specific purpose 

 of determining the effect of cold upon this parasite. It was noted, 

 however, that there was a large percentage of dead parasites in a 

 bulk collection of eggs obtained after the cold winter of 1917-18. 

 The locality from which this collection came has been used for a 

 number of years as a source of material for new colonies, and eggs 



