The nonperiodic population wave: a case study of the larch casebearer Protocryptis sibiricella (Lepidoptera, Coleophoridae)

Abstract

Biogeocenotic mechanisms of formation, existence, and extinction of sustained outbreaks of the larch casebearer Protocryptis sibiricella (Flkv.) were investigated from 1995 to 1998 in a forest-steppe larch forest at the Kuznetsk Alatau piedmont. Variation of the pest abundance within the sustained foci is determined by a complex of factors. The first factor is efficient adaptation of the pest to the condition of the host plant. The trophic behavior of the larch casebearer leads neither to permanent damage nor to a loss of stable resistance of the larch trees to secondary pests. Low flight activity of adults and preference of previously damaged trees for oviposition result in repeated infestation of the same larch stands. The second factor is degradation of pastures, which reduces the local abundance of the parasitoids of the casebearer and thus increases its survival rate. The third factor is the constant heterogeneous condition of the host plant which allows the sustained outbreaks of the phyllophage to exist for a long time. Extinction of sustained outbreaks may be caused by competitive interaction of phyllophagous insects, indirect influence of the host-plant pathogens or extreme abiotic factors.