THE RELATION OF TEMPERATURE TO THE ACTIVITY 

 AND CONTROL OF THE PLUM CURCULIO IN APPLES 



By W. D. Whitcomb 

 Assistant Research Professor of Entomology 



INTRODUCTION 



Although careful laboratory experiments (2, 9) have shown that lead arsenate 

 and other standard stomach poisons are strongly toxic to the plum curculio', 

 many fruit growers in Massachusetts have been unable to obtain satisfactory 

 control of this insect on apples by using these insecticides. This condition led 

 to an investigation of the factors which influence the activity of the plum cur- 

 culio in the hope of finding a practical index for more accurate timing of spray or 

 dust applications to combat this pest. Early in the work temperature was found 

 to play an important part in the problem, and the results of studies with this 

 factor are reported herein. 



SUMMARY OF SEASONAL HISTORY AND HABITS 



In order to connect the results of the experiments reported in this bulletin 

 with the normal activities of the plum curculio, the seasonal history and habits 

 of this insect are briefly summarized and a pictorial diagram is shown on the 

 opposite page. A complete discussion of these activities is presented in Massa- 

 chusetts Agricultural Experiment Station Bulletin 249. 



After spending the winter under leaves and brush in the vicinity of the or- 

 chard, particularly around stone walls, the beetles leave their hibernating quar- 

 ters with the approach of warm weather. The most adventurous of them appear 

 about the time the blossom buds show pink, but it is usually a week after the petals 

 have fallen before the majority of them are found in the trees. About half of 

 these beetles are males and half are females. The first beetles feed slightly on the 

 petals of the buds and blossoms but they eat very little until growing fruit is 

 available. When the fruit is about half an inch in diameter, it provides abundant 

 food and a suitable place for laying eggs, being most attractive to the beetles 

 at this stage of development. „ 



Both feeding punctures and egg punctures are made in the fruit. The former 

 are small round holes extending into the flesh about one-eighth of an inch, 

 while egg punctures are distinguished by a characteristic crescent-shaped cut 

 which partially surrounds the sunken egg and relieves the pressure of the rapidly 

 growing fruit. Insectary records in Massachusetts show that the beetles make 

 an average of 118 feeding punctures and that an average of 176 eggs are laid 

 during their normal life. The larvae or grubs hatch in about a week and imme- 

 diately tunnel toward the center of the fruit, requiring about 16 days of feeding 

 to become a full-grown grub. Almost without exception, an infested apple falls 

 to the ground before the grub has finished feeding, and about a week later the 

 grub leaves the apple to enter the ground where it forms a small earthen cell two 

 or three inches below the surface. The insect spends about a month in the soil 

 where it prepares for the resting period, performs the necessary transformations 



^Cono'.rachehts nenuphar Hcrbst. Family Curculionidae. Order Coleoptera. 



