Forest Pest Insects in North America: a Photographic Guide

Elongate hemlock scale

Fiorinia externa Ferris (Hemiptera: Diaspididae)

Orientation to pest

Elongate hemlock scale, Fiorinia externa Ferris, an invasive scale in the USA, is native to Japan and China that is a pest of eastern hemlock (Tsuga canadensis [L.] Carrière) in the eastern United States. The scale has long-lived adult females that reproduce slowly over much of the year, leading to a population with highly overlapping life stages. In New England there is one generation per year but there are two in North Carolina. Damage can be serious in eastern USA on hemlock, with densities 1-3 thousand-fold higher than in Japan, causing chlorosis, needle drop, and tree mortality.

Hosts commonly attacked

This scale attacks principally eastern hemlock (T. canadensis), but sometimes species of spruce or fir (Abies), Douglas-fir (Pseudotsuga menziesii [Mirbel] Franco), or yew (Taxus) are infested.

Distribution

Elongate hemlock scale is native to Japan and China but is invasive in North America from New Hampshire to Georgia and west to Michigan, within range of eastern hemlock. This scale is also invasive in Europe (UK, France).

Map of North American distribution of elongate hemlock scale USDA Forest Service - AFPE Online Mapping 1034x778
Figure 1. Map of North American distribution of elongate hemlock scale, Fiorinia externa

Images of elongate hemlock scale

Heavy infestation of elongate hemlock scale on eastern hemlock, showing many white males and some brown adult females Eric R. Day, Virginia Polytechnic Institute and State University, Bugwood.org 768x512 / 1536x1024
Adult female elongate hemlock scales (brown) Kristopher Abell, University of Massachusetts, Bugwood.org 768x512
Eggs (yellow) of elongate hemlock scale inside opened scale cover of adult female Pennsylvania Department of Conservation and Natural Resources - Forestry Archive, Bugwood.org 768x512 / 1536x1024
Settled first instar nymphs (see right colored, upper right quarter of photo) of elongate hemlock scale Rich Cowles, Connecticut Agricultural Experiment Station 768x512
Figure 2. Heavy infestation of elongate hemlock scale on eastern hemlock, showing many white males and some brown adult females Figure 3. Adult female elongate hemlock scales (brown) Figure 4. Eggs (yellow) of elongate hemlock scale inside opened scale cover of adult female Figure 5. Settled first instar nymphs ("crawlers", see right colored, upper right quarter of photo) of elongate hemlock scale
Second instar nymph (mid sized, yellow stages) of elongate hemlock scale; also showing  brown adult females and white males Pennsylvania Department of Conservation and Natural Resources - Forestry Archive, Bugwood.org 768x512 / 1536x1024
Adult female elongate hemlock scales with parasitoid emergence holes Kristopher Abell, University of Massachusetts, Bugwood.org 768x512
Adult Encarsia citrina, an often abundant but generally ineffective polyphagous parasitoid found attacking elongate hemlock scale in both North America and Japan Kristopher Abell, University of Massachusetts, Bugwood.org 768x512
An introduced predatory beetle that sometimes preys on elongate hemlock scale Pennsylvania Department of Conservation and Natural Resources - Forestry Archive, Bugwood.org 768x512 / 1536x1024
Figure 6. Second instar nymph (mid sized, yellow stages) of elongate hemlock scale; also showing brown adult females and white males Figure 7. Adult female elongate hemlock scales (left) with parasitoid emergence holes; adult Encarsia citrina (right), an often abundant but generally ineffective polyphagous parasitoid found attacking elongate hemlock scale in both North America and Japan Figure 8. Cybolephalus nr. nipponicus Endrody-Younga, an introduced predatory beetle that sometimes preys on elongate hemlock scale

Important biological control agents related to this pest species

Studies by Kristopher Abell (PhD dissertation, Entomology, University of Massachusetts, 2010) have shown that Encarsia citrina (Crawford), a polyphagous aphelinid parasitoid commonly found attacking elongate hemlock scale in both eastern North America and Japan, is only one of many Encarsia, Aphytis and other parasitoid species that attack the scale in Japan, which except for E. citrina are not present in North America. In addition, this same research has confirmed that E. citrina and the susceptible life stage of the scale are asynchronous throughout North America, even where two complete generations of the scale occur as Japan. The lack of synchrony was attributed to overlapping generations and delayed senescence of the adult female scale. Importations of species of parasitoids from Japan has potential to reduce densities of elongate hemlock scale in North America.

Web links for information on elongate hemlock scale

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