Hokkanen and Pimental (1984) suggested that natural enemies and their host plants that had coexisted for long periods evolved together to their mutual benefit, developing a homeostasis. For the natural enemies, this evolution tended away from traits that are detrimental to the plant and hence they are less likely to be the best agents. They concluded that the epicentre of evolution of the weed may not be the best place to search for potential control agents.

On the other hand, searching in areas relatively new to the plant may provide natural enemies that are more damaging and potentially better control agents, the hypothesis being that there had been less time for natural enemies to evolve homeostatic traits with their host plant. They suggest that exploration should take place on the edge of the weed's native range, or natural enemies would be sought on closely related plant species that have different geographical ranges to the target but that will also attack the target weed.

This concept may have a theoretical basis and there are practical examples, such as the most famous moth, Cactoblastis cactorum, from Argentina that controlled prickly pears that originated in Central America. However, exploration during modern projects includes collections from as wide a geographical source as possible, and most successful control agents have been found near the epicentre of the weed's native range.

The adult moth of Cactoblastis cactorum, an agent from Argentina that has
controlled cacti originating from Central America.

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