Daily thermoperiods of 27–18° C (square wave) induced diapause inMicroplitis croceipesin continuous darkness, whereas diapause was inhibited in continuous light. Scotophase temperatures were more important than photophase temperatures in diapause induction when photophase was held constant and scotophase increased (increasing light-to-dark ratio). Conversely, when scotophase was held constant and photophase was increased, diapause decreased. This suggests that the ratio of light to dark may be critical in diapause induction ofM. croceipes. In addition, diapause induction increased when low temperature coincided with the scotophase of the photoperiod.