PLUM CURCULIO IN APPLES 7 



per cage for each higher temperature group. Each cage contained 20 curcuhos 

 and the records were taken during the height of the curcuho activity in each 

 season, both egg punctures and feeding punctures being recorded. Observations 

 have indicated that the beetles are equally active when a maximum temperature 

 of 80° F. follows a minimum of 40° F. and when it follows a minimum of 50° F., 

 and it appears that maximum daily temperatures are as satisfactory as mean 

 daily temperatures for comparing thermotropic activity of adult plum curculios. 



Table 3. — Activity* of Plum Curculio Beetles Grouped According to Max- 

 imum Daily Temperature. Waltham, Mass., 1927-1930 



^Average daily punctures per cage of 20 beetles. 



Experiments at Controlled Temperatures in 1931 



In 1931 the activity of the plum curculio beetles was studied in the constant 

 temperature cabinets which were operated at 55 °, 65 °, 75 °, and 85 ° F. Two cages 

 of 10 beetles each were maintained at each temperature, and records of the 

 number of punctures in unsprayed fruit were made daily. 



At 55 ° F. the beetles were very sluggish but not entirely dormant since they 

 made an average of 1.025 punctures per day and laid a few eggs during the 

 first 10 days when activity is greatest. At 65° F. activity was nearly normal but 

 below the average for out-of-door conditions. The greatest number of punctures 

 was made at 75° F., although this exceeded the record at 85° F. very little. 

 The average of 6.675 punctures per beetle per day, as shown in Table 4, repre- 

 sents an increase of 277 per cent over this same activity at 65° F., and indicates 

 that 75 ° F. is very near the optimum temperature for activity. 



Table 4. — Activity* of Plum Curculio Beetles for Ten Days at Constant 

 Temperatures. Waltham, Mass., 1931 



Average Number of Punctures 

 Temperature 



Egg Feeding Total 



55° F 130 



65° F 445 



75° F 1.015 



85° F 1.035 



Normal outdoor** .210 



*Average number of punctures per curculio per day 

 **Average of insectary records for 3 years. 



THEORY OF RELATION OF TEMPERATURE TO TOXICITY OF 

 STOMACH POISONS TO THE PLUM CURCULIO 



When plum curculio beetles feed on fruit coated with lead arsenate or some 

 other arsenical poison they take small particles of the poison, particularly the 

 arsenic, into their stomach. The beetles may swallow the poison with their 



