Parasitism and predation as agents of mortality of winter moth populations in neglected apple orchards in Nova Scotia

This study compared the roles of pupal mortality and parasitism in winter moth ( Operophtera brumata ) population dynamics in Nova Scotian apple orchards and assessed the importance of beetles as pupal predators. The component of pupal mortality termed predation accounted for greater stage‐specific mortality of winter moth than parasitism by Cyzenis albicans in four neglected orchards. Parasitism by Cyzenis albicans was not spatially density‐dependent in any orchard, whereas the predation component of pupal mortality was spatially density‐dependent in the two orchards most densely populated by winter moth. Field experiments indicated that over 60% of pupal predation may be attributed to beetles, and that about 46% of pupal predation occurred within 4 weeks after pupal drop. Mortality of introduced populations of winter moth in Nova Scotia resembles that of native populations in England where density‐dependent predation regulates the winter moth population and reduces the parasitoid population to minimal levels. The situation in Nova Scotia appears to have changed appreciably since the establishment of parasitoids into the system in the 1950s.