Search

The hemlock woolly adelgid (HWA) (Adelges tsugae Annand) is an invasive insect in the eastern United States. Since its initial detection in Richmond, Virginia, in 1951, HWA has spread to half of the eastern hemlock (Tsuga canadensis (L.) Carr.) natural range. Detection of early infestation symptoms via remote sensing requires the knowledge of the changes in reflectance resulting from physiological changes in the host as inflicted by the insect and the selection of equipment with the appropriate sensor characteristics. Laboratory-based reflectance measurements of infested and non-infested hemlock foliage collected from four sites in southern New Hampshire and Maine occurred biweekly over 6 months in 2012 and weekly over 5 weeks in 2013. Vegetation indices (red edge inflection point (REIP), normalized difference vegetation index (NDVI), moisture stress index (MSI), and near infrared (NIR) 3/1 ratio) were associated with concurrent chlorophyll and moisture content data. Infested first-year foliage contained greater concentrations of chlorophyll and moisture, resulting in reduced visible spectral reflectance, greater REIP and NDVI values, and lower MSI and NIR 3/1 values than non-infested foliage. Furthermore, fluorescence measurements indicated greater photosystem function during the early stages of infestation, suggesting a possible compensatory response by hemlock to infestation. Significant differences in reflectance between infested and non-infested foliage were observed in late June and July in the weeks immediately following HWA settlement on new growth. Implementing these observations during remote sensing mission planning may increase the likelihood of detecting early HWA infestation symptoms at landscape scales. Key words: Adelges tsugae, hemlock woolly adelgid, remote sensing, vegetation indices, fluorescence, chlorophyll. Le puceron lanigere de la pruche (PLP) (Adelges tsugae Annand) est un insecte invasif dans l'est des Etats-Unis. Depuis qu'il a ete detecte pour la premiere fois a Richmond en Virginie, en 1951, le PLP a envahi la moitie de l'aire de repartition naturelle de la pruche du Canada (Tsuga canadensis (L.) Carr.). Pour detecter les symptomes precoces d'infestation au moyen de la teledetection il faut connaitre les changements dans la reflectance dus aux modifications physiologiques chez l'hote causees par l'insecte et choisir l'equipement dont les capteurs ont les caracteristiques appropriees. Des mesures de reflectance ont ete effectuees en laboratoire sur du feuillage de pruche infeste ou non preleve a quatre endroits dans le sud du New Hampshire et du Maine a toutes les deux semaines durant six mois en 2012 et a toutes les semaines durant cinq semaines en 2013. Des indices de vegetation (REIP, NDVI, MSI et NIR 3/1) ont ete associes aux donnees simultanees de teneur en humidite et en chlorophylle. Le feuillage d'un an infeste contenait de plus fortes concentrations de chlorophylle et d'humidite qui se traduisaient par une diminution de la reflectance spectrale dans le visible, des valeurs plus elevees de REIP et NDVI et plus fables de MSI er NIR 3/1 que dans le feuillage non infeste. De plus, des mesures de fluorescence ont montre que le photosysteme fonctionnait davantage durant les premiers stades de l'infestation, ce qui suggere possiblement une reaction compensatoire de la pruche a l'infestation. Des differences significatives de reflectance entre le feuillage infeste et non infeste ont ete observees a la fin du mois de juin et en juillet durant les semaines qui ont immediatement suivi l'etablissement du PLP sur les nouvelles pousses. L'integration de ces observations durant la planification des missions de teledetection pourrait augmenter les chances de detecter les symptomes precoces d'infestation du PLP a l'echelle du paysage. [Traduit par la Redaction] Mots-cles: Adelges tsugae, puceron lanigere de la pruche, teledetection, indices de vegetation, fluorescence, chlorophylle., 1. Introduction Eastern hemlock (Tsuga canadensis (L.) Carr.) is a foundation tree species in the northeastern United States (Ellison et al. 2005). Often found on steep slopes and in riparian [...]

Reoccurring seasonal cyanobacterial harmful algal blooms (CHABs) persist in many waters, and recent work has shown links between CHAB and elevated risk of amyotrophic lateral sclerosis (ALS). Quantifying the exposure levels of CHAB as a potential risk factor for ALS is complicated by human mobility, potential pathways, and data availability. In this work, we develop phycocyanin concentration (i.e., CHAB exposure) maps using satellite remote sensing across northern New England to assess relationships with ALS cases using a spatial epidemiological approach. Strategic semi-analytical regression models integrated Landsat and in situ observations to map phycocyanin concentration (PC) for all lakes greater than 8 ha ( n = 4117) across the region. Then, systematic versions of a Bayesian Poisson Log-linear model were fit to assess the mapped PC as a risk factor for ALS while accounting for model uncertainty and modifiable area unit problems. The satellite remote sensing of PC had strong overall ability to map conditions (adj. R2, 0.86; RMSE, 11.92) and spatial variability across the region. PC tended to be positively associated with ALS risk with the level of significance depending on fixed model components. Meta-analysis shows that when average PC exposure is 100 μg/L, an all model average odds ratio is 1.48, meaning there is about a 48% increase in average ALS risk. This research generated the first regionally comprehensive map of PC for thousands of lakes and integrated robust spatial uncertainty. The outcomes support the hypothesis that cyanotoxins increase the risk of ALS, which helps our understanding of the etiology of ALS. [ABSTRACT FROM AUTHOR]