The ability to survive winter temperatures is a key determinant of insect distributional ranges and population dynamics in temperate ecosystems. Although many insects overwinter in a state of diapause, the hemlock woolly adelgid [Adelges tsugae (Annand)] is an exception and instead develops during winter. We studied a low density population of A. tsugae, which undergoes two generations per year, in a forested area in which its only available host plant, eastern hemlock (Tsuga canadensis), was patchy and scarce. In January 2014, this area also experienced an exceptionally cold winter due to a southward shift in the North Polar Vortex. We used 3 years of systematic sampling prior to the 2014 cold wave, and 1 year following, to quantify the effect of the 2014 cold wave on A. tsugae population dynamics. We observed a strong negative correlation between the number of days below sub‐zero temperature thresholds and A. tsugae, and estimated that the 2014 cold wave resulted in at least a 238% decrease in its population growth rate. However, we also observed that the detrimental effect of the 2014 cold wave to A. tsugae was short‐lived, as populations measured in the late summer of 2014 rebounded to pre‐2014 cold wave densities. This study highlights the effect that cold winter weather events can have on a winter active insect species, and the speed at which populations can recover from stochastic mortality events.
With the challenges that negatively impact tree-based agriculture, landscapes and forests, such as climate change, plant pathogen and insect range expansion, invasive species and limited new pesticides, it is important to introduce new and effective tree protection options. In the last 20 years, pathogens that invade wood i.e. vascular tissues of trees causing wilt, yellowing, premature defoliation, cankers and tree death, have been on the rise. Diplodia corticola causes Bot canker of oak species which can kill trees diminishing the valuable ecological services they provide and reducing profits from wood and cork production. Since this and similar pathogens have difficult biologies because they reside in wood and cause severe internal damage and tree death, their management is difficult or inefficient with classical pesticide application methods that cannot reach and distribute the active ingredient in vascular wood tissues. As practical management options for this and other vascular tissue pathogens of trees are limited, we evaluated efficacy of several trunk injected fungicides in control of D. corticola and compared it with the efficacy of trunk injection of similar compounds for control of Venturia inaequalis and Erwinia amylovora, as two well-studied apple tree pathogens with different or partially similar lifestyles to D. corticola, respectively.
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