Factors Affecting Insect Population Dynamics: Differences Between Outbreak and Non-Outbreak Species

Even though outbreaks of insects are temporally rare events, they have aroused the interest of theoretical and applied entomologists alike. The pop­ ulation dynamics of spatially rare species have been the subject of long-term studies concerned with the extirpation of these species, the unusual habitats they occupy, or the unique adaptations they possess (5, 107, 112) . A compari­ son of the features of insects possessing different population processes may lead to a more thorough understanding of insect population dynamics. Past Annual Review of Entomology articles have addressed a number of population dynamics topics including density dependence (100), life tables (54), dynam­ ics (160), stability and diversity (153), and pest management (159). However, no review has specifically addressed insect pest outbreaks or attempted to compare population dynamics of outbreak and nonoutbreak species. Richards (118) pointed out that this comparison is essentially an issue of popUlation balance versus population fluctuation. Populations of organisms are never truly stable, but rise from some low density and then fall to approximately their original size. They may exhibit stable equilibrium points, stable cyclic oscillations between two popUlation points, stable cycles, or a regime of aperiodicity (87). Insect pests usually