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

Abstract

1. This study compared the roles of pupal mortality and parasitism in winter moth (Operophtera brurnata) population dynamics in Nova Scotian apple orchards and assessed the importance of beetles as pupal predators.2. 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.3. 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.4. 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.

Survey for Winter Moth (Lepidoptera: Geometridae) in Northeastern North America with Pheromone-Baited Traps and Hybridization with the Native Bruce Spanworm (Lepidoptera: Geometridae)

“…If this functional immunity to C. albicans has a genetic basis, then this trait also could pass from Bruce spanworm to winter moth via hybridization. In Nova Scotia and British Columbia it seems that winter moth remains under good biological control, but research by Roland (1990Roland ( , 1994 in British Columbia and Pearsall and Walde (1994) in Nova Scotia suggests that it is predators and not C. albicans that maintains winter moth at innocuous densities. Indeed, the rates of parasitism in both of these regions by C. albicans are much lower now than the rate reported by Embree (1965) after the initial introduction.…”

Different impact of pupal predation on populations of Epirrita autumnata (Lepidoptera; Geometridae) within and outside the outbreak range

“…Especially pupal predation is considered to have a regulating effect on many lepidopteran populations (East 1974; Bechinski & Pedigo 1983; Bauer 1985; Weseloh 1990; Walsh 1990; Cook, Hain & Smith 1994; Pearsall & Walde 1994). In E. autumnata, the difference in the length of summer between the north and the south is adjusted by altering the duration of pupal period, which lasts about one and half months in northern and about 3 months in southern Fennoscandia.…”

Variation in Captures of Adult Winter Moths (Operophtera brumata) in Coastal Maine Over Two Years

“…Research by Pearsall and Walde (1994) in Nova Scotia also supports this view. They showed that mortality in low-density populations in apple orchards was dominated by pupal predation and that parasitism by C. albicans varied between 4 and 28%, far lower than the initial values in 1960-1962 reported by Embree (1966) (Fig.…”

“…Winter moth densities there declined to innocuous levels, but so did parasitism by C. albicans. Parasitism values on the order of 5% have been reported there in subsequent years (Pearsall and Walde 1994). So it appears that C. albicans serves to knock down high densities of winter moth, which are then maintained at lower densities by other factors, such as pupal predation (Roland 1994).…”