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Differential sunlight exposure affects settling behaviour of hemlock woolly adelgid crawlers

Formally Refereed
Authors: Albert E. Mayfield, Robert M. Jetton
Year: 2020
Type: Scientific Journal
Station: Southern Research Station
Source: Agricultural and Forest Entomology


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.


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


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