SUMMARY OF INSECT CONDITIONS DURING 1921. 3 



states are Idaho, Nevada, and Utah, also practically all 

 above the 3.000-foot elevation line. The Southwestern States are 

 Arizona and New Mexico. The remaining three States are called 

 the Pacific Coast States. 



In the temperature and precipitation studies being made by the 

 survey, departures from the normal instead of means are being 

 used. Acute outbreaks undoubtedly are reflections of abnormal 

 meteorological conditions (plus or minus departures) associated with 

 other limiting factors, otherwise they would be chronic conditions 

 and not acute outbreaks. 



As data accumulate, the regions over which certain pests are 

 chronic will define themselves, and the normal meteorological range 

 for these regions will be the range of optimum effectives for the given 

 pest. Then a study of the means in other regions should be an index 

 to the possibility of acute outbreaks in these regions. On the other 

 hand, pronounced departures from the normal over the region of 

 optimum effectives for a given pest should be reflected by an abnor- 

 mal reduction in the abundance of that pest. 



During the entomological season of 1021. starting in September. 

 1920, the weather over the entire region east of the Rocky Moun- 

 tain and ^Southwestern States was marked by much wider departures 

 from the normal in both rainfall and temperature than over the 

 Western States. The weather in Xew England and in the Middle 

 Atlantic and South Atlantic State- was characterized by a slight 

 excess of temperature and a more pronounced excess of precipita- 

 tion in September, 1920. especially in the northern portion. In 

 October the temperature excess increased, while generally over the 

 region there was a very marked deficiency in rainfall. Xovemh'-r 

 was generally deficient in temperature, except in the Middle Atlantic 

 States, while the rainfall was excessive. December. January. Feb- 

 ruary, and March were warm throughout the entire region, the excess 

 increasing as the winter advanced. Very -erious freezes occurred 

 March 28 and 29 over the lower Middle Atlantic and northern South 

 Atlantic States. The rainfall in December was exeessive. except in 

 central and western Virginia, while during the remainder of the 

 winter it was below normal. April was generally warm, with about 

 normal rainfall: two severe killing frosts, however, did further seri- 

 ous damage during this month throughout the Middle Atlantic and 

 South Atlantic States. During May, in Xew England and the 

 northern Middle Atlantic States, temperature was about normal. In 

 the South Atlantic States the temperature was low and the rainfall 

 excessive. The remainder of the summer was above normal in tem- 

 perature with the exception of August, which was a little deficient. 

 The rainfall during the summer was very seriously below normal, 

 being relieved in the Xew England and South Atlantic States in July, 



