The Effect of Pupal Predators on a Population of Winter Moth, Operophtera brumata (L.) (Hydriomenidae)

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Abstract
Thenumber of winter moth larvae failing to pupate from a group of oak trees in the study area at Wytham, Berkshire, in 1965, was estimated to be about 269/m2, of which some 238 were healthy. It has been estimated, by analogy with other years, that about 190 of these will have been killed by predators or factors other than the pupal parasite Cratichneumon culex. An unknown number of the larvae was killed before pupation by surface-active predators of various species. Some 95 of the resultant pupae were taken by adults of the carabid genera Pterostichus and Abax, and by adults of the staphylinid Philonthus decorus, of which P. decorus took the largest proportion by virtue of its large population size. A further unknown number was taken by elaterid larvae. The shrew Sorex araneus probably accounted for about 25 pupae, and other small mammals may have taken an equal number. On emergence, the moths were again subject to the attack of surface-active predators. It is indicated that predation on winter moth pupae is density dependent. The way in which the density-dependent relationship might function is suggested.

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