419 



ever, coincide almost exactly with the velocities for the larva in the apple as 

 derived by entirely different methods (see Table V), up to SO" F. The top 

 of the curve for the larva in the apple is about four velocity units lower at 

 the maximum (see broken-line peak in Pig. 24.) This is in accord with ex- 

 pectation, as the larva in the center of the apple would probably not be warmed 

 to the same extent as the larva in the cocoon, during the brief period of dally 

 maximum temperature. 



(D) VELOCITIES AS AFFECTED BY FACTORS OTHER THAN 

 TEMPERATURE AND HUMIDITY. 



The foregoing considerations of the development of the codling moth 

 have been presented with reference to temperature and humidity ns if no 

 other factors operated to modify the results. It remains to consider how 

 other factors modify the velocity values based on temperature and 

 humidity data. The following are known to be of importance: (1) varia- 

 bility of temperature and humidity, (3) rainfall which soaks the larvae 

 or pupae, (3) wind or air movement, (4) qtiality and intensity of light, 

 (■3) food, (6) mechanical stimuli, (7) seasonal march of temperature and 

 humidity. 



(1.) Variability of Temperature and Humidity in Weather Condi- 

 tions. 



Variability of weather conditions has to be considered, first, from two 

 view-points: (a) variation of temperature and humidity in the form of 

 daily rhythm, as contrasted to constant temperatures; (b) rising and fall- 

 ing of general temperature for the day, as shown by higher or lower 

 maxima, minima, and means, under actual weather conditions. 



(a) All available data on pupae, taken together, indicate that the 

 length of the stage under variable temperatures is approximately 7 per 

 cent shorter than under constant temperatures, although no experiments 

 were especially designed to verify this difference. Such experiments, to 

 give results comparable with those tmder actual weather conditions, would 

 have to include temperatures outside the straight-line limits. The crucial 

 experiments AD and A\\' (Fig. 15), with temperatures varying slowly 

 within the straight-line limits, showed the same acceleration as the weather 

 conditions. In some exceptional experiments, however, with small num- 

 bers of individuals, when the temperature rose suddenly and dropped 

 again within a few hours, the velocity seemed to be decreased as com- 

 pared with that for the corresponding constant temperatures. Although 

 this retarding effect was obscured by other variations in conditions, the 

 fact deserves mention, and the exceptional data are listed here : In one 

 case, the temperature varied 4°-10° F. during 2 hotn-s at mid-day, being 

 constant most of the other hours, and the velocity was decreased 9 per 

 cent. In another case (two lots of presumably uniform material in the 

 1917 experiments), with a rise of 15°-20° F. at mid-day, which is of 

 the order of magnitude of the out-door rise in otir region, the velocity 

 dififered by 12 per cent as follows: in constant conditions, with tempera- 

 ture 69.5° and humidity 80 per cent, the pupal time was 13.1 days; in 



