Tit Predation and the Abundance of Ernarmonia conicolana (Heyl.) on Weeting Heath, Norfolk, 1962-63

Abstract

Measurements are given of the abundance of over-wintering larvae of the eucosmid moth Ernarmonia conicolana (Heyl.) in cones of scattered Scots pines (Pinus sylvestris) in 1962/63 and of predation upon the larvae by tits (parus spp.). The number of larvae on different trees varied from none to 79 per 50 cones. Larvae were distributed very unevenly on the area, but there tended to be more larvae per 50 cones on trees with many heavily infested neighboring trees within 50 m than on other trees. Predation by tits varied on different trees according to the abundance of the larvae, reaching 60% on trees with 50-60 larvae per 50 cones. Percentage predation was slightly higher on larvae in cones with many than with few larvae per cone. Larvae were concentrated on the outer faces of the cones, and suffered heavier mortality there than did those on the inner faces of the cones. About 14% of the larvae that survived predation by tits failed to complete their life cycle, and 3.7% of all larvae were parasitized by the ichneumon Ephialtes laticeps Ratz. Statistical evidence implies that very few developing larvae died as a result of intraspecific competition, and that total mortality other than that caused by tits was probably slight.