329 



In the present paper, Glenn's data have been worked over in con- 

 junction with new data, and the conception of development here pre- 

 sented is based upon the actual behavior of the codling moth both under 

 controlled experimental conditions and also under actual weather condi- 

 tions. Only indirect use, however, is made of weather records. The 

 results of laboratory experiments and of outdoor observations have been 

 quite fully correlated, we believe, for the first time. The results have 

 also been compared with the more important investigations of the last 

 century and found to be in accord with the general results hitherto 

 obtained. 



A new method for estimating the progress of life-history stages is 

 herein described, which affords a basis for taking humidity into account 

 directly and other factors less directly. The factors secondarily consid- 

 ered are the rainfall during preceding months and the seasonal march of 

 temperature. In the interpretation of the effects of these factors, the 

 value of the climatic diagrams of Taylor ('1-1) and the observations of 

 Huntington ('19) on man have been confirmed for the codling moth. 

 Furthermore, the findings of Krogh relative to development taking place 

 below the starting point, as ordinarily assumed or ascertained, have 

 been confirmed. 



Conditions Affecting the Rate of Development. 



The most important growing-season factor influencing the develop- 

 ment of animals native to moist or rainy climates, is usually temperature, 

 for it is the most variable. It changes almost continuously throughout any 

 twenty-four-hour period, being usually highest about 2 P. M. and lowest 

 about 6 A. M. The duration of minimum temperature varies consider- 

 ably with the length of day and night, and the duration of maximum 

 temperature also varies ; both vary with other weather conditions. The 

 daily march of temperature (from higher to lower and from lower to 

 higher) is irregular on stormy and cloudy or partly cloudy days. 



Humidity is probably second in importance to temperature; at least, 

 it is such a continuously accompanying variable of all temperatures and 

 of all temperature changes that it cannot be ignored. The daily march 

 of humidity is fully as striking as that of temperature. Usually, how- 

 ever, when the temperature rises, the humidity falls ; and I'icc versa. 

 The humidity accompanying any given temperature varies with the time 

 of year, amount and frequency of precipitation, cloudiness, etc. There 

 is no constant or dependable association between the two which can be 

 expressed in numerical values. 



Rainfall influences the rate of development of organisms in a less 

 direct but nevertheless very important way. The amount of rainfall in 

 autumn and winter influences the codling moth's rate of development in 

 spring, probably also its winter survival, undoubtedly its vitality, and 

 hence its rate of increase and success in general. 



Air movement afifects the organism by controlling the rate of evapo- 

 ration, or withdrawal of water from the organism. Intensity of light and 



