THE CODLING MOTH IN MICHIGAN. 



37 



respective days. To show the extent of variation in results obtained, 

 the maximum and minimum of average temperatures of individual 

 pupal stages are given for the different days in the same table. On 

 examining the diagram of figure 13 it will be noted that where the 

 averages have been made from a large number of observations the 

 results are fairly uniform. These results here show a marked de- 

 crease in the time of the pupal stage with an increase of temper- 

 ature. Considering the curve of this figure we get the following 

 readings : 



°F °C 



For the 15 days pupal stage 09.2 or 20.6 



F< >r the 17 days pupal stage 67.3 or 19.6 



For the 19 days pupal stage 66.0 or 18.9 



For the 21 days pupal stage 65.1 or 18.4 



It should be remembered that besides the temperature there are 

 other factors affecting the development of the insects. Moisture 

 and the physical condition of individual insects, etc., naturally tend 

 to cause variation in the length of the pupal stage, and to these 

 factors may be ascribed certain variations in the results obtained. 



SPRING BROOD OF MOTHS. 



Time of emergence of moths. — The earliest moths, emerging May 26, 

 were about normal in the date of appearance. Subsequently, how- 

 ever, and for the rest of the emergence period, the moths appeared 

 very irregularly and for a longer period than usual. At the height of 

 the emergence, during the middle part of June, two fairly long delays 

 were caused by prevailing rains and a drop of temperature, so that 

 the emergence period, as shown in figure 14, became marked by two 

 distinct maximums. The records for the emergence of 1,127 moths 

 are given in Table XXXVI. The first moth of the summer brood 

 emerged July 7 and the last moth of the spring brood emerged July 

 8, thus causing the emergence periods of the two broods to overlap. 



Table XXXVI. — Time of emergence of moths of the spring brood, Douglas, Mich., 1911, 



Total, 1,127 moths. 



