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    Author(s): Albert E. Mayfield; Robert M. Jetton
    Date: 2020
    Source: Agricultural and Forest Entomology
    Publication Series: Scientific Journal (JRNL)
    Station: Southern Research Station
    PDF: Download Publication  (787.0 KB)

    Description

    1 Previous research demonstrated that elevated sunlight improves carbon balance and growth of eastern hemlock (Tsuga canadensis (L.) Carrière) seedlings infested with the invasive hemlock woolly adelgid (Adelges tsugae Annand).
    2 This study examined the hypothesis that elevated visible and ultraviolet sunlight directly affects the settling behaviour of A. tsugae crawlers.
    3 Hemlock seedlings were manually infested with equal densities of A. tsugae and placedintoartificialshadetreatments(0%,40%and80%shade).Thedensityofsettled nymphsoftheensuinggenerationonshadedseedlingswasthreetimeshigherthanthe density on unshaded seedlings.
    4 Adelges tsugae ovisacs were also attached to hydrated hemlock branches placed beneath acrylic filter treatments that selectively allowed transmission of various sunlightwavelengths.Theproportionofadelgidcrawlersthatsettledonthebranch(vs. dropping from it) was higher beneath filters that blocked the widest spectrum of solar radiation (opaque and amber filters) than beneath full sun. In the March-April trial, exposure to full sun and the full visible spectrum only (clear-UV filter) significantly increased the proportion of crawlers that settled on the bottom (vs. top) side of the branch.
    5 Our results suggest that A. tsugae crawlers are negatively phototactic and/or thermotactic, with behaviour influenced more by visible light than ultraviolet light.

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    Citation

    Mayfield, Albert E.; Jetton, Robert M. 2020. Differential sunlight exposure affects settling behaviour of hemlock woolly adelgid crawlers. Agricultural and Forest Entomology. 56: 59-. https://doi.org/10.1111/afe.12382.

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    Keywords

    Adelges tsugae, eastern hemlock, forest insects, invasive species, negative phototaxis, shade, Tsuga canadensis, ultraviolet light, visible light.

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