ENTOMOLOGY

104 SANITARY ENTOMOLOGYI:lThere is a rule which receives much support, that a given reactionor stage of development is accomplished at an almost constant totaleffective temperature, which i.s the multiple of time units by temperatureunits accumulated above the zero· of effective temperature. Since thezero varies with t}:te humidity, the total effective temperature obtaInedby this rule does likewise. We must therefore reword the rule to read:A. given reaction or 8tag~ of development is accomplished at any givenmean humidity at a constant total effective temperature, which is themultiple of effective time units by temperature wnits accumulated withinthe zone of effective temperatures at a given· atmospheric pressure.To compute this one must fhost eliminate all time, temperature,and humidity which waS noneffective, whether at the top or bottom of thescale. For instance, if at 60% humidity the temperatures 65° to 85°are effective, and during the day the temperature ranged from '50° to 90°,but only during eight hours at the effective t.emperatures; we mustmultiply the period 8 hours by the mean temperature experienced between65° and 85°, considering 65 as 0 and 85 as ~O. The result isthe total effective temperature of that day. Adding these total effectivetemperatures during the total period of the stage, we obtain the totaleffective temperature necessary to bring about the perfection of thestage. Necessarily this is a very complicated proposition, l"equiringvery careful computations.. Nevertheless, once worked out we can establishlaws of control which are of utmost ~alue.Some of the following lectures will refer to the principles laid downin this lecture and lines of research will be suggested leading towardcontrol measures. The charts (figs. 8, 9) should be studied in connectionwith the lecture.