Population collapses in a forecasted outbreak of Lambdina fiscellaria (Lepidoptera : Geometridae) caused by spring egg parasitism by Telenomus spp. (Hymenoptera : Scelionidae)

A major outbreak of the hemlock looper, Lambdina fiscellaria (Guenee), pred icted for 1997 on the Gaspe Peninsula in Quebec, collapsed due to egg paras itism by Telenomus spp. Only 3,857 ha of balsam-spruce forest were defoliat ed from the forecasted 130,000-ha outbreak area. This represents only 3% of the anticipated outbreak area. We present data that indicate highly effici ent natural control by Telenomus sop. The L. fiscellaria population also co llapsed due to egg parasitism by Telenomus spp, on Anticosti Island in the same year. In the past, L. fiscellaria egg parasitism has usually been esti mated from egg samples collected in the fall or early spring surveys and wa s based mostly on the eggs' black coloration. However, our observations ind icate that entirely black and opaque eggs result from parasitism by Trichog ramma spp., those attacked by Telenomus spp, varying from translucent to da rk brown but always showing a single dark spot on the chorion. Moreover, ou r data on seasonal egg parasitism showed important and rapid increases in p arasitism Ly Telenomus spp. in late spring. Therefore, similar unexplained L. fiscellaria outbreak collapses that occurred in the past might have also been caused by egg parasitism by Telenomus spp. There are several species in the Telenomus complex attacking L. fiscellaria and the most abundant one might be a "keystone species" in the population dynamics of this defoliato r. The spring activity of Telenomus spp. ma), lead to errors when forecasti ng L. fiscellaria populations based only on fall egg surveys.