Correctly timing the break of diapause and reactivation of development is critical for synchronizing the insect with its food source as well as optimizing mating opportunities. In many cases, diapause is actually broken (i.e., the insect is capable of developing) in early winter, but the progression of development is suppressed by the prevailing low temperatures. This post-diapause quiescence is followed by resumption of development when temperatures rise above a developmental threshold in the spring. This mechanism allows insects that have entered diapause at different times to be stockpiled in post-diapause quiescence and then develop synchronously in the spring. Alterations in the timing of spring development have led to host plant specialization and speciation. Several environmental factors, including chilling, daylength, rainfall patterns, and food availability, exert an influence on diapause duration, and an internal energy-sensing mechanism plays a key role in monitoring levels of energy reserves available to the insect.