32 



BULLETIN 265, U. S. DEPARTMENT OF AGRICULTURE. 



RELATION OF TEMPERATURE TO DEVELOPMENT. 



Temperature has a very decided influence on the development of 

 insects. Within certain limits increased temperature will hasten 

 development, other factors being equal. The dock false-worm 

 seemed peculiarly susceptible to changes in temperature, and it has 

 already been noted that all stages of its development were shorter 

 in the summer than in the spring. For example, the incubation 

 period of the first-brood eggs (April-May) averaged 10.7 days, while 

 that of the second-brood eggs (June-July) averaged only 4.8 days. 

 Some observations were made on the length of the pupal stage, 

 which, while not taking into consideration the possible effect of differ- 

 ences in humidity and other factors, show very definitely the effect 

 of changes in temperature. The temperature records were obtained 

 from a Richard thermograph placed in the rearing shelter. A sudden 

 rise or fall of temperature hastened or retarded adult emergence. 

 Before April 16 the temperature had only occasionally got above 70° 

 F. From April 16 to 19, inclusive, the daily maximum was above 80° 

 F., and the daily minimum about 50°, whereas it had been about 40° 

 previously. The sawfly pupa? responded to this rise in temperature, 

 and on two days, April 18 and 19, 20 adults emerged from pupae 

 that had pupated during a period of eight days, or from April 5 to 

 12, inclusive. 



Table XXIII compares the length of the pupal period with the 

 average temperature. This temperature was obtained as follows : The 

 average daily temperature was computed by the sufficiently accurate 

 method of averaging the daily maximum and minimum. Then the 

 average temperature for each individual was obtained by adding 

 the daily averages for the pupal period (including the day of pupation 

 and the day of emergence) of that individual, and dividing by the 

 number of days. The average temperature for a pupal period of any 

 given number of days was then obtained by simply adding the 

 average temperatures of all individuals having a pupal period of 

 that number of days and dividing by the number of individuals. In 

 all, the average temperatures for 137 pupse of the spring brood and 

 first brood were computed, pupae from unfertilized eggs not being 

 considered. 



Table XXIII. — Length of pupal period of the dock false-worm compared with the average 

 temperature, Wenatchee, Wash., 1915. 



Pupal period in days. . 



14 



13 



12 



11 



10 



9 



8 



7 



6 



5 



4 



Average temperature 

 in ° F 



55. 31 



55.88 



57.65 



58. 12 



58.29 



58.62 



59.66 



61.65 



66.60 



67.94 



70.60 











0.57 



1.77 



0.47 



0.17 



0.33 



1.04 



1.99 



4.95 



1.34 



2.66 









