Green lacewings (Chrysoperla rufilabris (Burmeister)) are a potential biological control agent for balsam twig aphid (Mindarus abietinus (Koch)), the only major insect pest of balsam and Fraser fir Christmas trees in Michigan.  Our objective was to evaluate the potential for augmentative biological control of balsam twig aphid using commercially available green lacewings.  In 2000 and 2001 we evaluated the efficacy of C. rufilabris for control of balsam twig aphid in laboratory trials and under field conditions.  In the laboratory, we determined that larvae of C. rufilabris readily consumed balsam twig aphids and completed development from first instar to pupation in four to seven days.  C. rufilabris larvae required a diet of at least ten aphids per day to complete their development.   We also monitored C. rufilabris feeding and searching behavior in lab trials.  When C. rufilabris larvae were caged on tree branches infested with balsam twig aphid, the C. rufilabris larvae significantly reduced the number of aphid eggs deposited.  We released C. rufilabris larvae onto infested balsam firs in three commercial Christmas tree fields. In these fields, we monitored the aphid population during the growing season, the damage caused by balsam twig aphid, and the number of aphid eggs deposited.  In one field with a high balsam twig aphid population, C. rufilabris larvae significantly reduced the aphid population.  The two remaining fields had moderate aphid infestations and the C. rufilabris larvae reduced the aphid population in one field but not the other.  Our results indicate that C. rufilabris may be an effective biological control of localized balsam twig aphid populations.