The rate of hatch of overwintered eggs of the strawberry aphid, Chaetosiphon fragaefolii (Cockerell), at five temperatures in controlled environment chambers was used to determine the thermal threshold of development. Samples of eggs were taken from two field locations several times before hatch. These samples were subdivided and placed into two or three different constant temperature chambers. The day-degree requirements for hatching from the time of collection were estimated. These estimates corresponded to the number of day-degrees actually accumulated in the field between the time of egg collection and the time of hatching.
This method of simulating the effect of temperature on egg development was an accurate method of predicting the time of hatch in the field at least 3 weeks prior to the observed time.