Establishing Diadromus pulchellus for biological control of leek moth, Acrolepiopsis assectella: How many does it take?

Diadromus pulchellus Wesmael (Hymenoptera: Ichneumonidae) has been introduced into North America for biological control of the leek moth, Acrolepiopsis assectella Zeller (Lepidoptera: Acrolepiidae), an alien pest of Allium spp. Since 2010, field releases of more than 10,500 females have been made at multiple sites. In each of 2011, 2012, and 2013 progeny of D. pulchellus females that overwintered have been recovered. This suggests that establishment has occurred but is this the case?