THE PLUM CURCULIO IN APPLES 



39 



Figure 7. Time when Larvae of Plum Curculio Left the Fruit in Breeding 

 Cagres in the Insectary, "Waltham, Mass. 



NATURAL CHECKS ON ABUNDANCE 



Climatic Conditions 



Several observations in Massachusetts indicate that 60 per cent to 75 per 

 cent of the pkim curculio beetles die in their hibernating quarters, the num- 

 ber depending on the amount of snow and the frequency of sudden changes 

 from high to low temperatures. This percentage may seem high in view of 

 the abundance of beetles in the orchards m the spring, yet in 1927-28, an 

 unusually open winter, several cages of beetles with a six-inch covering of 

 leaves, some exposed and othei's protected by a roof suffered 90 per cent to 

 100 per cent mortality. 



During the summer, when infested fallen apples are exposed for two or 

 three days to a bright hot sun, many of the larvae die in the frTiit. However, 

 the shade from the tree and the protection from grass or mulch usually 

 eliminate high mortality from this cause. 



Baking and packing the soil around the cells in which the insects are 

 pupating prevents many of the beetles from emergmg, but again such con- 

 ditions seldom occur in this state. 



