Prey Density and Rates of Predation by Tits (Parus Spp.) on Larvae of Codling Moth (Cydia pomonella) under Bark

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Abstract
In a cider-apple orchard near Bristol [England, UK] in late Jan. 1972 (Experiment 1) and Dec. 1972 (Experiment 2), fully grown larvae of the codling moth were allowed to select cocooning sites under the bark of apple logs about 2 m long, 1-30 larvae/log. Logs were then tied into large trees. Within the 1st 18 or 19 days, blue tits (P. caeruleus) and sometimes also great tits (P. major), reduced the larvae on logs with 4 or more larvae initially to a mean number of 1.8/log which is a spatially density-dependent mortality. Tits destroyed the remaining larvae at intervals through winter and spring. In Experiment 2 the mortality appeared density-dependent through time, i.e., a smaller percentage of the larvae present was taken in successive periods as number declined. This was not established for Experiment 1, but the percent mortality declined along with the numbers of tits seen frequenting the orchard. In an aviary, blue and great tits initially explored a log bearing codling larvae under the bark and, on finding and eating a larva, search intensively, usually beginning near the site of the catch (area-restricted searching) and continued intensive searching until they found no more. This mode of hunting was probably responsible for the rapid early removal of larvae from logs in the orchard. Exploratory (i.e., less intensive) searching was seen in the orchard as well as in the aviary; repetition of this, when larvae had become too sparse for area-restricted searching to succeed, could account for the slow loss of larvae through the winter. Bird predation may regulate the codling moth population through successive years in this unsprayed orchard.