Host Tree Species Affects Spruce Budworm Winter Survival.

With current trends in global warming, it has been suggested that spruce budworm outbreaks may spread to northern parts of the boreal forest. However, the major constraints for a northward expansion are the availability of suitable host trees and the insect winter survival capacity. This study aimed to determine the effect of larval feeding on balsam fir, white spruce and black spruce on various spruce budworm life history traits of both the parental and the progeny generations. Results indicated that the weight of the overwintering larval progeny and their winter survival were influenced by host tree species on which larvae of the parental generation fed. White spruce was the most suitable host for the spruce budworm, producing the heaviest pupae and the heaviest overwintering larvae while black spruce was the least suitable, producing the smallest pupae and the smallest overwintering progeny. Overwintering larvae produced by parents that fed on black spruce also suffered higher winter mortality than individuals coming from parents that fed on balsam fir or white spruce. With current trends in global warming, spruce budworm is expected to expand its range to northern boreal forests where black spruce is the dominant tree species. Such northern range expansion might not result in outbreaks if low offspring winter survival on black spruce persist.

Hydroxyacetophenone defenses in white spruce against spruce budworm.

We review a recently discovered white spruce (Picea glauca) chemical defense against spruce budworm (Choristoneura fumiferana) involving hydroxyacetophenones. These defense metabolites detected in the foliage accumulate variably as the aglycons, piceol and pungenol, or the corresponding glucosides, picein and pungenin. We summarize current knowledge of the genetic, genomic, molecular, and biochemical underpinnings of this defense and its effects on C. fumiferana. We present an update with new results on the ontogenic variation and the phenological window of this defense, including analysis of transcript responses in P. glauca to C. fumiferana herbivory. We also discuss this chemical defense from an evolutionary and a breeding context.

Effect of temperature and host tree on cold hardiness of hemlock looper eggs along a latitudinal gradient.

The hemlock looper, Lambdina fiscellaria, is an economically important insect pest of Canadian forests which overwinters as eggs. Although the hemlock looper causes extensive damages, no information on the mechanisms related to its cold tolerance is known. The objective of this study was to determine the effect of temperature and exposure duration on hemlock looper winter survival but also to identify seasonal supercooling capacity and cryoprotectant levels of three populations along a latitudinal gradient. As host plant may contribute to offspring overwintering success, cold tolerance of hemlock looper eggs from parents whose larvae were fed on three different tree species was also measured. Mean supercooling point (SCP) of hemlock looper eggs was lower than -30 °C from October through the following spring with values being as low as -47 °C in February. Trehalose was the most abundant sugar found in hemlock looper eggs with a peak concentration of 0.3 µg mg⁻¹ DW⁻¹. Glycerol, a polyol, was more often absent in eggs of the different populations and tree species tested in the study. When exposed to different temperature regimes for various periods of time, significant mortality of hemlock looper eggs occurred at higher temperatures than the mean SCP. Thus, hemlock looper could be considered as a chill tolerant species. No clear pattern of population and host plant effects on SCP and cryoprotectants was detected in this study. However, when exposed to different winter temperatures and exposure duration, hemlock looper from higher latitudes survived better (survival rates ranging between 0 and 89% at -20 °C) than those from lower latitudes (survival rates ranging between 0 and 56% at -20 °C). Our results may contribute to a better understanding of hemlock looper winter biology and thus facilitate predictions of outbreaks and range expansion.