80 NEW YORK STATE MUSEUM 



19 14 inclusive, so that comparison may be made between the two 

 years 19 12 and 19 14 when unusually low temperatures checked the 

 normal breeding of the elm leaf beetle, and those of 191 o, 1911 and 

 1 9 13, years when the insect was rather destructive and therefore 

 presumably not checked by weather influences. The important 

 period, as noted above, comprises June nth to 20th, and the tem- 

 peratures of 191 2 should be compared with those for corresponding 

 dates above or below and those for 19 14 with the three normal years. 

 It will be observed at once that the minimum temperature dropped 

 considerably lower and more frequently during these two years, 

 falling in 191 2 to 38 on the 14th and to 46 or 45 on the 13th, 15th and 

 19th. There is a fall, though proportionately less, in the maximum 

 temperatures. Somewhat the same conditions obtained during this 

 ten-day period in 19 14, except that the cool weather came from the 

 1 6th to the 20th, there being a period of six successive days, if we 

 count the 2 1st, when the minimum ranged from 52 to 39. There was 

 also a perceptibly lower maximum. 



Adding the maximum and minimum temperatures and both com- 

 bined, also given in our temperature tabulation, we likewise find 

 during this ten-day period, a markedly lower average than for the 

 same periods in the other years. This is so evident that we would 

 suggest the following as a tentative rule : when the sum of the maxi- 

 mum and minimum temperatures (F.) for a ten-day period for or 

 about the middle of June does not exceed 1250 units, the probabilities 

 are that egg laying will be checked and that an unusual mortality 

 will occur in both eggs and young grubs. 



