Gli:.\.\; Ln sect Development. 323 



the stages of a given inseet, the constant of the equation for the 

 wliok^ period fi-oni the deposition of the egg to tlie emergence of 

 the adult may be found by adding the constants of the equations 

 of the stages, and, by making suitable allowance for the time which 

 elapses between the emergence of the adult and the deposition of 

 eggs, a formula for the whole life cycle of the insect may be de- 

 termined. 



These equations may be of i)ractical value in several ways. 



By computing the normal daily effective day-degrees in any lo- 

 cality, the number of generations of the insect in that locality, and 

 the normal dates on which the first eggs, or larvae, may be expected 

 to appear in that place can be ascertained. If any part of the 

 season should be abnormally cold or warm, the amount of retard- 

 ation or acceleration in development can be computed by keeping 

 a daily record of the effective day-degrees and comparing them 

 with the normal temperatures. In this way we should be able to 

 ascertain when the injurious phase of any insect pest is approach- 

 ing long enough beforehand to enable us to take whatever pre- 

 cautionary measures are necessary to avoid injury. 



In the case of the codling moth, the dates when the larvae of each 

 generation may be expected to enter the fruit can be determined 

 long enough beforehand to enable the owners to apply the spray 

 at the right time. 



How well this method of forecasting insect injuries will work out 

 in practice only time can tell ; however, the plan seems to be a 

 feasible one. and one worth investigating. 



