DOI: 10.5061/dryad.t175g
title: Data from: Mechanisms underlying spruce budworm outbreak processes as elucidated by a 14-year study in New Brunswick, Canada

description: We conducted a 14-year intensive study of spruce budworm (Choristoneura
 fumiferana (Clem.)) survivorship at three study plots in largely balsam
 fir (Abies balsamea (L.) Mill.) stands in New Brunswick, Canada, to
 elucidate certain key mechanisms underlying spruce budworm outbreak
 cycles. The study covered a peak-to-declining phase (from 1981 and 1994)
 of the budworm outbreak cycle that had started in the early 1960s.
 Frequent sampling was carried out in each plot-year to construct a
 practically continuous survivorship curve, and the annual variation in
 population density was estimated. We found a high level of correlation
 between the studied phase of the outbreak cycle and annual variations in
 the survivorship over the postdiapause period, suggesting that
 postdiapause survivorship was the chief determinant of the cycle. We found
 the annual changes in population density in the present study to be
 closely similar in pattern to those from the provincial budworm surveys
 conducted in much larger areas. This implies that the mechanism underlying
 the population process found in the few study plots in largely balsam fir
 stands also applies to the process in much larger areas of diverse stand
 types. The main source of postdiapause mortality is found to be natural
 enemies. The impacts of parasitoids and disease are evaluated by rearing
 budworm samples in the laboratory. Hymenopteran and dipteran parasitoids
 are by far the major sources of mortality, and microsporidians are the
 most prevalent pathogen. Occurrences of other entomopathogenic fungi and
 viruses were insignificant throughout the study. Seasonal changes in
 laboratory survivorship are compared with the corresponding field
 survivorship to estimate the effect of predation. No major mortality
 factor is found to singly play a predominant role in determining the
 outbreak cycle. Conversely, some minor factors are shown to have played
 significant roles. Thus, the importance of recognizing the action of
 natural enemies as a complex is emphasized for understanding the budworm
 outbreak cycle. Finally, centered around the roles played by the
 chronological succession of natural enemies in the present study, the
 results of budworm research in New Brunswick since the mid-1940s are
 synthesized to outline basic mechanisms underlying the outbreak processes
 as a guide for further studies.
description: Numerical data for Fig.
 2.Densities of spruce
 budworm (numbers per 1 m2 of branch surface area) in Plot 1 of: (A)
 postdiapause larvae, pupae, and pupal exuviae: (B) eggs. Year is calendar
 yearNumericalData_Fig2.xlsxNumerical data for Fig. 3.Densities of spruce budworm (numbers per 1 m2 of branch surface area) in Plots 2 and 3 of: (A) postdiapause larvae, pupae, and pupal exuviae: (B) eggs. Year is calendar year and Date, ordinal date.NumericalData_Fig3.xlsxNumerical data for the solid-circle series in Fig. 11.Realization of survivorship (% of the initial cohort) in laboratory rearing of postdiapause spruce budworm samples from Plot 1. Year is calender year and Date, ordinal date.NumericalData_Fig11.xlsxNumerical data for the solid-circle series in Fig. 12.Realization of survivorship (% of the initial cohort) in laboratory rearing of postdiapause spruce budworm samples from Plots 2 and 3. Year is calender year and Date, ordinal date.NumericalData_Fig12.xlsxNumerical data for parasitism and disease in Fig. 15.Numerical data for parasitism and disease in Fig. 15.NumericalData_Fig15.xlsx