COMMON MECHANISMS UNDERLYING CONTRASTING DYNAMICS IN 2 POPULATIONS OFTHE PINE LOOPER MOTH

1. Census data from an outbreaking population of the Pine looper moth, Bupalus piniaria L. (Lepidoptera: Geometridae) are used to derive a l ife-table for the population. 2. A comparative analysis is made of thi s life-table with one published for a non-outbreaking population of th e moth. 3. The stage-specific survival rates are found to exhibit qual itatively similar patterns, though the absolute survival rates differ substantially in some cases. 4. There is evidence for the operation of density-dependent processes at several points in the moth's life-cycl e. 5. The results of published experimental studies are used in derivi ng proposals for the mechanisms underlying the patterns of stage-speci fic survival. 6. Finally, it is suggested that the underlying mechanis ms are fundamentally similar in both populations and that differing en vironmental conditions modulate the differential expression of these m echanisms in the two populations, so generating the observed differenc es in their population dynamics.