Regulatory processes and population cyclicity in laboratory populations of Anagasta Kühniella (Zeller) (Lepidoptera: Phycitidae) II. Parasitism, predation, competition and protective cover

Summary The population dynamics of Anagasta kühniella has been studied in standardized conditions in replicated ecosystems in which the variables have been increased one at a time. Additional to the variables reported earlier (WHITE and HUFFAKER, 1969), the present ecosystems included larval and pupal parasitism by Venturia canescens , both in the presence and absence of the egg‐predator Blattisocius tarsalis , and also in the presence and absence of two levels of protective cover for the host. In the presence of V. canescens , parasitism was generally of major importance as a regulating instrument in determining host population densities and it characteristically produced cycling and discrete host generations that arose from a parasite‐induced discontinuity in the age‐structure of the host populations. When the predatory mite and/or protective cover was also present, modifying interactions arose but these were not sufficient to dispel completely the discontinuous age‐structure and the cycling induced by the parasite. The actual degree of protective cover was particularly important insofar as it modified the levels and patterns of parasitism and permitted competition for food among host larvae to assume greater importance in the collective regulating process. Three forms of population cyclicity are described and discussed: a four‐generation cyclicity which was the basic pattern of cycling and occurred both in the presence and absence of protective cover; an eight‐generation cyclicity that arose from disturbed four‐generation cycling in the presence of a minimal level of host protection; and a nine‐generation cyclicity in which extensive protection compounded the collective nature of density‐dependent regulation.