PLITM CURCULIO IN APPLES 



11 



depositing eggs, and, therefore, are subjected to curculio attack earlier and over 

 a longer period. In Massachusetts, Duchess, Gravenstein, and Baldwin are 

 very susceptible, while Mcintosh is the least susceptible of the common com- 

 mercial varieties. 



Appearance of Hibernating Curculios in the Trees 



High temperatures which stimulate feeding and oviposition by the curculio 

 beetles also hasten the rapidity with which they leave their winter cover and 

 congregate in the trees. 



In seasons such as 1931 (Figure 3) when a period of warm weather comes 

 soon after the petal-fall stage, the greatest population of curculios in the trees, 

 as well as the greatest activity of the beetles, occurred in the same period, mak- 

 ing the prompt application of control measures doubly imperative. It may hap- 

 pen, however, that moderately high temperatures have caused a large number 

 of beetles to enter the trees without inducing excessive activity or injury to the 

 fruit, and this condition is followed by a period of cool weather with the maxi- 

 mum temperatures usually below 60° F., which greatly decreases the acti\ity of 

 the beetles. In this case the presence of the beetles in the trees is relatively 

 unimportant, except that the control treatments must be applied promptly with 

 the approach of maximum temperatures above 75° F. Such a condition was 

 approached in 1930 as indicated in Figure 4. 



Figure 4. — Relation of Maximum Daily Temperatures to the Activity of the 



Beetles During the Critical Period for Control of the Plum Curculio. 



Waltham, Mass., 19.?0 



/9 20 PI £2 £3 £4 £S £6 £728 29 AO 3/ 



£ i 4 S 6 

 JUNE 



Average number of punctures per day by 10 beetles in insectary. 

 Average maximum daily temperature in insectary. 



Climatic Conditions Influencing Control in 1930 



In 1930, the climatic conditions immediately following the petal fall of apples 

 represented well defined extremes, as sho''Arn in Figure 4. The calj^x spray was 

 applied from May 17 to 19, and was followed by two days of cool weather. On 

 May 22, the ma.ximum temperature jumped to 81° F., and reached 74° F. on 



