Laricobius nigrinus Fender is being reared for release as a biological control agent for hemlock woolly adelgid (HWA), Adelges tsugae Annand. HWA is an introduced insect lethal to hemlock trees (Tsuga canadensis (L.) Carr. and T. caroliniana Engelm.) in the eastern United States. In nature, the predator (Laricobius nigrinus) and its prey (HWA) undergo a dormant period in the summer (aestivation). In the laboratory, the aestivation of L. nigrinus has not been synchronized with that of HWA, resulting in significant predator mortality. Four factors (genetics, temperature, photoperiod, and moisture) were investigated for their effects on aestivation in L. nigrinus. Both the number of individuals and the time at which they emerged from aestivation were measured in response to these factors. Temperature was the most important cue for termination of aestivation, and photoperiod was a modifying factor. High temperature and long day length delayed emergence and high moisture levels resulted in greater emergence but did not affect emergence time. Genetics, as represented by broods, was not a major factor in aestivation termination. These results have led to improvement in rearing L. nigrinus, since emergence from aestivation can now be synchronized with the active period of HWA. Increased success in rearing has expedited field releases of L. nigrinus in the eastern United States.