Technical Abstract: Populations of hymenopteran parasitoids associated with immature stages of the invasive emerald ash borer (EAB) Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) were surveyed in 2009 and 2010 in the recently invaded areas in Michigan, where the two introduced EAB larval parasitoids, Tetrastichus planipennisi Yang and Spathius agrili Yang were released for classical biological control. Results from the two years of field surveys showed that several hymenopteran parasitoids have become associated with EAB in Michigan. Among these parasitoids, the gregarious species T. planipennisi was the most abundant, accounting for 93% of all parasitoid individuals collected in 2009 (immediately after field release) and 58% in 2010 (a year later after field releases); low levels (1–5%) of parasitism of EAB larvae by T. planipennisi were consistently detected in the survey sites in both years. Separately, the abundance of the native parasitoid Atanycolus spp. increased sharply, resulting in an average parasitism rate of EAB larvae from <0.5% in 2009 to 19% in 2010. Other parasitoids such as Phasgonophora sulcata Westwood, Spathius spp, Balcha indica Mani & Kaul, Eupelmus sp, and Eurytomus sp. were much less abundant than T. planipennisi and Atanycolus spp, and each caused less than 1% of the EAB parasitism. Besides hymenopteran parasitoids, woodpeckers consumed 32 – 42% of all the immature EAB stages present at our study sites while undetermined biotic factors (such as microbial disease and host tree resistance) caused 10–22% mortality of the observed EAB larvae. Findings of our study showed that both introduced and exotic hymenopteran parasitoids (along with woodpeckers and undetermined biotic factors) may contribute significantly to the reduction of EAB populations and ash mortality in the invaded areas of North America.