Biological Control in Native and Introduced Habitats: Lessons Learned from the Sap-Feeding Guilds on Hemlock and Pine
Many of most important and destructive pests are herbivorous insects that were introduced from abroad. Surprisingly few studies have examined the impact of natural enemies on the population dynamics of introduced pests in their homelands. There are many possible constraints on successful biological control of introduced pests. The common paucity of taxonomic and bionomic information on pests and their natural enemies in their homeland is among the most obvious and significant of these constraints. The chapter discusses the various constraints on successful biological control in introduced habitats and offers alternate strategies and approaches that may enhance the usefulness of studies of pests in their native habitats for biological control of introduced pests. None of the predators and parasites that attack the introduced adelgid and scale pests in eastern North America are effective biological control agents. Density-dependent feedback has a major impact on the population dynamics of exotic guild species on hemlock and pine.