An endophytic fungus interacts with crown level and larval density to reduce the survival of eastern spruce budworm, Choristoneura fumiferana (Lepidoptera: Tortricidae), on white spruce (Picea glauca)

Abstract

A two-year field study was carried out to determine whether inoculating white spruce, Picea glauca (Moench) Voss, with a native endophytic fungus, Phialocephala scopiformis DAOM 229536 Kowalski & Kehr (Helotiales, Ascomycota), decreased the performance of eastern spruce budworm, Choristoneura fumiferana Clemens, developing on these trees. Second instars were reared at three densities in the mid crown and at one density in the lower, mid, and upper crown. Larval survival (i.e., survival of larvae to pupation) was lower on endophyte-inoculated trees than on control trees in the mid crown and especially the upper crown but was similar in the lower crown, resulting in a significant interaction between endophyte and crown level. A similar but marginally insignificant interaction was observed for overall survival up to adult emergence (i.e., total survival). Larval survival and total survival were approximately 22% and 19% lower, respectively, when developing in the upper crown of endophyte-inoculated trees than in control trees. Larval survival remained relatively constant, with increased density on control trees but decreased with density on endophyte-inoculated trees, resulting in a significant interaction between endophyte and larval density. Sex ratios of emerged adults and wing lengths of emerged females were not influenced by the endophyte. Our results suggest that endophytic fungi could be useful additions to integrated pest management programs.

A Conceptual Framework for the Spruce Budworm Early Intervention Strategy: Can Outbreaks be Stopped?

“…Development or integration of other tactics that can add mortality while avoiding interference with natural enemies (e.g., tree resistance, biological control, semiochemical control) could further increase EIS efficiency and efficacy [62,63].…”

Influence of a Foliar Endophyte and Budburst Phenology on Survival of Wild and Laboratory-Reared Eastern Spruce Budworm, Choristoneura fumiferana on White Spruce (Picea glauca)

“…Under nursery conditions, most of the effect was attributed to the presence of the anti-insect toxin rugulosin [10]. Building on those studies, we recently demonstrated a similar effect on budworm developing on white spruce trees that had been inoculated with the endophyte more than 10 years earlier [11]. The reduction in budworm survival was highest for larvae developing in the mid and upper crown of trees, the most important crown region for photosynthesis and tree growth.…”

“…Field experiments were carried out near Havelock, New Brunswick in two adjacent "test plots" (45 • 587" N, 65 • 26" W) of approximately 10-year-old white spruce, Picea glauca (Moench) Voss, trees planted by JDI Limited from seedling stock in 2003. Test plots are described in our previous study [11]. Briefly, both untreated control and endophyte positive trees were interplanted at 2 m × 2 m spacing in each of two adjacent 0.12 ha plots.…”

“…Here, we report results from a manipulated field study carried out to investigate the independent and interacting effects of the endophyte, P. scopiformis, larval source (wild or laboratory-reared), and budworm spring emergence-host plant budburst synchrony on the performance of spruce budworm. As in our previous study [11], the present study was carried out with relatively low budworm densities, and subsequently low levels of defoliation. The objective was to determine whether the endophyte would reduce budworm survival before a large outbreak occurred.…”

“…In our previous study [11], laboratory-reared second-instar budworm were placed on trees in the field on a single date. Consequently, we do not know if the endophyte is as effective on wild as lab-reared budworm or during years when spring synchrony between larval emergence and budburst varies.…”