Jens Roland

Large scale forest fragmentation increases the duration of tent caterpillar outbreak

I examined historical data (1950–1984) on the duration of outbreaks of the forest tent caterpillar (Malacosoma disstria) in northern Ontario, Canada. Outbreak duration was compared to host tree species dominance and forest structure over large areas of boreal forest partially cleared for agriculture. Abundance of the principal host tree species Populus tremuloides had no consistent effect on duration of outbreak within forest districts, and was negatively correlated with duration of outbreaks among the eight forest districts examined. The amount of forest edge per km2 was the best, and most consistent, predictor of the duration of tent caterpillar outbreaks both within individual forest districts and among forest districts. Because forest tent caterpillar populations are driven largely by the impact of parasitoids and pathogens, results here suggest that large-scale increase in forest fragmentation affects the interaction between these natural enemies and forest tent caterpillar. Increased clearing and fragmentation of boreal forests, by agriculture and forestry, may be exacerbating outbreaks of this forest defoliator.

Melanism and diel activity of alpine Colias (Lepidoptera: Pieridae)

SummaryThe hypothesis that increased melanism provides a benefit in prolonging diel activity through more efficient absorption of solar radiation was tested in the field on a population of alpine Colias sulphur butterflies. A marked increase in the duration of flight and feeding behaviour existed for melanistic individuals when compared to lighter individuals under cool temperatures and low intensity solar radiation. More melanistic butterflies moved longer distance per day, and emigrated from the population at a faster rate. At high temperature and high radiant load lighter coloured individuals appeared more active. This is the first field demonstration of the advantage of melanism for increasing activity of ectotherms in cold environments.

Improved insect performance from host-plant defoliation: winter moth on oak and apple

ABSTRACT. 1. We test the hypothesis that defoliation has short‐term and long‐term negative effects on performance of winter moth Operophtera brumata L. on two species of food plants: Garry oak (Quercus garryana Dougl.) and apple (Malus domesticus L.).

After the Decline: What Maintains Low Winter Moth Density after Successful Biological Control?

Life-table data for winter moth are analysed for an 8-year period following introduction of parasitoids for biological control in British Columbia, Canada. Winter moth density declined in 1984, and has remained low since 1985 at an average density of approximately 1.20 adults per m 2 . Introduced parasitoids contributed to mortality during the decline, and have a weak, delayed density-dependent effect at the new low density. Mortality of unparasitized pupae in the soil (primarily by predation) is strongly, and directly density-dependent at the new low density, and is the factor which is most strongly regulatory. Analysis indicates that the strong regulation of winter moth numbers by generalist predators allows parasitism levels to vary greatly after suppression without the eruption of winter moth populations; if parasitism were absent, winter moth populations would erupt to pre-biocontrol levels

Foraging pattern of pine siskins and its influence on winter moth survival in an apple orchard

SummaryForaging by migratory pine siskins in an apple orchard infested with varying densities of winter moth was observed, and winter moth mortality in the presence and absence of birds was recorded. Time spent foraging in a tree and number of birds foraging per tree was positively related to larval density but number of larvae removed per leaf cluster or per unit time was not. Level of defoliation was a better predictor of the number of clusters searched per tree than was prey density. Despite poor predictability in allocation of search effort with respect to prey density, siskins acted as a source of strong compensatory mortality on the winter moth population.

Response to Bonsall & Hassell `Identifying Density-Dependent Processes: A Comment on the Regulation of Winter Moth'

The re-analysis by Bonsall & Hassell (1995) questions the validity of analysing population data over a limited range of population densities rather than analysing the entire data set. My use of a restricted set of data points for analysis of winter moth populations in British Columbia, Canada (Roland 1994) was not done with respect to density per se, but rather was restricted to a given time interval which happens to