PLUM CURCULIO IN APPLES 5 



REACTION OF FRUIT INSECTS TO TEMPERATURE 



Studies of the relation of temperature to the development and activity of 

 insects have been reported by several investigators, and among fruit insects the 

 codling moth has received particular attention of this nature. It is well known 

 that the female codling moth will lay few if any eggs when the temperature is 

 below 60° F., while Glenn (3) and Shelf ord (7) have completed a long series of 

 experiments showing the number of accumulated "hour degrees" above a certain 

 "threshold temperature" that are necessary for the completion of each biological 

 development in the codling moth. With these data they are able to predict in 

 advance with considerable accuracy the reactions which climatic conditions will 

 exert on the insect in the orchard. Later, Peterson and Haeussler (6) found that 

 the oriental peach moth had temperature requirements similar to those reported 

 for the codling moth by Glenn (3). The reactions of the plum curculio at con- 

 trolled temperatures are not known to have been reported previously. 



EFFECT OF TEMPERATURE ON THE PLUM CURCULIO 

 Development of Immature Stages 



When confined at 55' F., all eggs, larvae, and pupae which were under obser- 

 vation failed to develop. Death appeared to be due to an excessive retardation 

 of biologic development rather than to any sudden shock from low temperature. 

 The eggs were observed in their natural location in punctures in small apples, 

 and it was usually two or three times the normal incubation period before the 

 egg collapsed and it could be definitely determined that it would not hatch. 

 Mature larvae in soil began pupation but died before the distinguishing pupal 

 characters developed. 



At 65° F., development was completed, but the incubation of the egg and 

 the period spent in the soil as mature larva, pupa, and adult were considerably 

 longer than under normal outdoor conditions. The feeding period of the larva 

 in the apple was about normal though slightly shorter than under outdoor con- 

 ditions, and it appears that this stage of the insect is practically immune to 

 reasonable variations in air temperature, or that the green apple provides good 

 insulation. 



At 75° F., development was considerably more rapid than normal in all stages 

 except the feeding period of the larvae in the apple. The greatest increase in 

 rapidity of development occurred between 65° and 75° F., and 75° F. appears 

 to be very near the optimum temperature for the development of the plum 

 curculio. The change at 85 ° F. was so slight as to be insignificant and there was 

 a slight retardation in the larval feeding period at the higher temperatures. 

 A summary of this development is presented in Table I. 



Table I. Development of Immature Stages of Plum Curculio at Constant 

 Temperatures. Waltham, Mass., 1931 



Average Number of D.\ys Required For: 

 Temperature 



Incubation Feeding of Development of 



of Egg Larva Larva, Pupa, and 



Adult in S->il 



55° F. Development not completed 



65° F 11 13.75 37.75 



75° F 3.8 13.87 22.50 



85° F 3.08 15.00 21.85 



Normal outdoor* 7.1 16.09 30.54 



♦Average of insectary records for three years. 



