Many organisms have been introduced from their native areas to foreign lands, some with disastrous results. In the absence of naturel en enemies, populations of organisms such as the gypsy moth and the fire ant reach uncontrollable levels.
Similar results are possible when naturel enemies of native organisms are eliminated.
Torolf Torgersen is an entomologist with the U.S. Forest Service's Pacific Northwest Forest and Range Experiment Station in La Grande, Oregon. He has been studying one example in Pacific Northwest forests, the effects of birds and other naturel enemies on two forest insect pests, the Douglas-fir tussock moth and the western spruce budworm. He is using the findings of these studies to emphasize to forest managers the need to provide for the wellbeing of these naturel enemies and thus prevent pest outbreaks. The first step in studying the effects of naturel enemies is to identify which organisms are the predators. In one of Torgersen's studies, a branch stocked with a known quantity of Douglas-fir tussock moth larvae or pupae was observed from a blind some distance away.