Host races of the apple maggot, Rhagoletis pomonella, produce pupae that can undergo one of three developmental pathways: direct development (non-diapause), a shallow diapause and a cold-dependent diapause of long duration. To understand what influences this decision; we collected wandering larvae of both host races (apple and hawthorn) from a field site (Grant, MI) in August and September of 2004. We separated them, ten days after pupariation, into four treatment groups: 25°C, 4°C for 16 weeks, 4°C for 25 weeks and a frozen control. We monitored wet and dry weight, energy reserves and a genetic profile based on allozyme differences in an attempt to establish a correlation with the incidence of diapause and diapause duration. We found that the apple race is on average heavier than the hawthorn race. However, weight was not found to correlate with diapause incidence. We are currently conducting energy reserve analysis and allozyme frequency determinations to investigate linkage with diapause status. Clearly a shift in the timing of diapause induction and termination was critical in enabling the native hawthorn race (fall fruiting) to make the shift to summer-fruiting apples.