Adventive and potentially pestiferous species are a constant threat to the agriculture of Florida. Fiorinia externa Ferris (Hemiptera: Diaspididae), the elongate hemlock scale, is a recent but persistently intercepted pest of Fraser fir and related species grown out-of-state and imported annually into Florida as cut Christmas trees. Although this and a second species, Hemiberlesia ithacae (Ferris) (Hemiptera: Diaspididae), the hemlock scale, may not become established in Florida on native or cultivated hosts, the risk remains and illustrates the importance of continued vigilance against pest species incursion.
In preparation for the Christmas holiday season, various conifer tree species are imported by retailers into Florida during Nov and Dec for sale as cut Christmas trees. All commercial agricultural products, including imported Christmas trees, are subject both to border inspection and follow-up import inspection at the store or tree lot by the Florida Department of Agriculture and Consumer Services, Division of Plant Industry (FDACS-DPI). Not surprisingly, some insect, spider, and mite species are collected from trees during inspection. Many are incidental, widespread, and present no risk, but several intercepted species are not known to occur in Florida and when found elicit a regulatory response, such as quarantine, treatment, or destruction. The most commonly imported Christmas tree species are Abies species (“firs”), in particular Abies fraseri (Pursh) Poir (Pinaceae). Although firs do not occur naturally in Florida, some species may rarely be grown as ornamentals, and many related conifer species occur in Florida either as part of native plant communities or as economically important commodities (e.g., pines, Pinus spp.) or landscape species.
Since 2012, DPI inspectors surveying imported Christmas trees have collected elongate hemlock scale, Fiorinia externa Ferris (Hemiptera: Diaspididae), a scale species not present in Florida. In Dec 2015, specimens of Hemiberlesia ithacae (Ferris) (Hemiptera: Diaspididae), the hemlock scale, were collected from A. fraseri Christmas trees grown in North Carolina. Hemlock scale has not previously been collected in Florida from imported Christmas trees, and like elongate hemlock scale, has potential host overlap with species that occur in Florida and is therefore a quarantinable pest. Import records indicate that most cut trees are imported from North Carolina, but also in lesser numbers from other eastern US states such as Virginia and Pennsylvania.
Fiorinia externa was described in 1912 from specimens collected in Maryland from hemlock (Tsuga spp.; Pinaceae), but almost certainly is native to Asia (Ferris 1942). The scale now occurs throughout hemlock forests in the temperate eastern United States. Hemiberlesia ithacae was described in 1883 from specimens collected in New York, also from hemlock, and is now widely distributed throughout the United States (García et al. 2015a,b). Hemlock scale was described in the genus Aspidiotus but transferred to Abgrallaspis, the combination under which most literature was published, and recently moved to Hemiberlesia (Normark et al. 2014); it is unclear to what region of the world hemlock scale is native.
Both species develop on the underside, or abaxial surface, of the needle, but the shape of the cover of each species is distinct, a distinction in part reflected in the common name of F. externa, the elongate hemlock scale. Like the several related species of Fiorinia known in Florida, such as F. theae Green (tea scale) and F. fioriniae (Targioni Tozzetti) (many common names, camellia scale), elongate hemlock scale is longer than wide, whereas the scale cover of H. ithacae, like that of the common species H. lataniae (Signoret) (latania scale), is roughly circular in outline. Scale cover formation in armored scales was summarized by Stoetzel (1976). Fiorinia proboscidaria Green (no common name), a potential pest of citrus, was recorded as a new continental record in 2013 (Stocks 2015) and should be consulted for additional images for comparison with F. externa. Fiorinia species differ significantly from most armored scale species in that the adult female remains contained within the exuviae, or cuticle, of the proceeding stage, a condition termed “pupillarial.” The habitus descriptions below pertain only to specimens on Abies, because specimens from other hosts have not been intercepted.
The adult female of F. externa (Fig. 1) is pupillarial, with the 2ndstage exuviae dark brown, ∼3 times longer than wide, and glossy. The exuviae of the crawler, or 1st-stage nymph, is attached terminally to the exuviae of the 2nd stage. Covers of other stages, such as developing males, with small amounts of attached wax may also occur on the needle (Fig. 1d), and yellow crawlers occur under or near the adult females, or are active on the leaf prior to settling. The pupillarial condition of the female makes it difficult to determine if it is still alive, but when observed with a 10–20× hand lens, living females or crawlers often are evident if the cover is opened. Submitted samples have varied from low levels of infestation with few living specimens to heavily infested ones with a high percentage of living scales of all stages. In some specimens, the cover varies along its length from an opaque light brown to dark brown; crawlers, embryonic cuticles, or crawler egg-shells can be seen beneath the exuviae in the opaque region, whereas the body of the female is shriveled toward the opposite end (Fig. 1a and c). The contours of the fir needle, as seen in cross section, create submarginal abaxial (ventral) “troughs” on each side of the mid-line in which the crawlers settle and develop. Each trough is covered by a white, waxy material (epicuticular wax; Fig. 1e) that protects the needle and the lines of respiratory stomata on the needle surface (Trimble et al. 1982).
The scale cover of adult females of H. ithacae (Figs. 2–4) is subcircular and varies in color from light brown to dirty gray. In general, the cover resembles that of H. lataniae and other aspidiotine scale insects, in which the scale cover of the adult female is composed of the cen trally or subcentrally located exuviae of the crawler (yellow to gold in color) and concentric layers of waxy material secreted by the female during growth. In this species, the exuviae of the 2nd stage is not integrated into the waxy material and is therefore not visible unless the cover is lifted and the female below is exposed. As noted above for elongate hemlock scale, this species also may become partly covered by the epicuticular wax, and in some instances the scale may appear to be striped (Figs. 3b and 4).
Multiple ages and remains of dead specimens are commingled on the needle (Fig. 4), but adult females can be located if the scale cover is gently lifted from the needle surface; adult females are golden-yellow and subcircular in outline (Fig. 2). For both species, identification is based on micro-anatomical structures observed in slide-mounted adult females.
Neither species has been reported on trees in the wild in Florida, but both are known as far south as Georgia, at least where appropriate hosts and conditions are present (García et al. 2015a, b), and F. externa is recorded throughout the temperate and boreal regions of Asia (China, Japan; Garcia et al. 2015a, b). Both species are restricted to conifers, but the host range of elongate hemlock scale is wider and includes, in addition to Pinaceae, hosts in the families Cupressaceae and Taxaceae (Garcia et al. 2015a,b).
Hemiberlesia ithacae hosts: Abies spp. (firs); Picea spp. (spruces); Pseudotsuga menziesii (Douglas fir); Tsuga spp. (hemlocks).
Fiorinia externa hosts: In addition to those listed for hemlock scale, hosts include Cupressaceae (Juniperus spp.), Taxaceae (Taxus sp.), and the genera Cedrus and Pinus (Pinaceae).
In Florida, hemlock, spruce, and fir do not occur naturally, and generally do not perform well under cultivation; thus, hemlock scale may not thrive in Florida. Conversely, many pine species (Pinus spp.) are either native to Florida or commercially cultivated, and Cedrus deodara (Roxb.) G. Don f. (deodar) and C. libani A. Rich (Lebanon cedar), and many Juniperus species (Cupressaceae) are common landscape ornamental plants.
As documented hosts occur in the families Pinaceae and Cupressaceae, an expanded risk analysis based on potentially suitable hosts suggests that species in the families Taxaceae, Araucariaceae, and Podocarpaceae be evaluated as alternate hosts (e.g., Christenhusz et al. 2011). In Florida, Taxaceae include the critically endangered Florida torreya (Torreya taxifolia Arn.) and Florida yew (Taxus floridana Nutt. ex Chapman) as potentially suitable hosts. However, Jill Sidebottom, extension forestry integrated pest management specialist for North Carolina State University, who has extensive experience with both scale species and their economic and ecological impacts, did not find the scale during surveys of cultivated Florida torreya at the Biltmore Estate in Asheville, North Carolina, or of naturally growing stands in Torreya State Park, Florida (pers. comm.). No native species of Araucariaceae or Podocarpaceae occur in Florida, but both families include commercial ornamental species, such as the Norfolk Island pine (Araucaria heterophylla [Salisb.] Franco) and several species or varieties of podocarpus (Podocarpus spp., Afrocarpus sp.). Although both scale species may be economic pests under certain circumstances, biological controls (parasitoids and predators) are effective in suppression when part of an integrated pest management program (Jill Sidebottom, pers. comm.).
The phenomenon by which developing scale covers may acquire attributes of the substrate, such as by “burrowing” under the upper dermal layer, is well documented (e.g., mining scale, Howardia biclavis [Comstock], Miller & Davison 2005; Diaspis gilloglyi McKenzie, McKenzie 1963) and presumably confers additional environmental protection to the scale or enhances crypsis. If the scale is transferring by some mechanism the epicuticular wax to the cover, it is likely to have a detrimental effect on the needle beyond that due to feeding. Epicuticular wax prevents condensation from blocking the stomata, thereby reducing gas exchange, and as such is integral to the proper physiological function of the needle (Jenks & Ashworth 1999).
The author extends his thanks to the many dedicated plant inspectors whose efforts help protect Florida's agriculture and native plants, and especially Lisa Hassell. Marc Frank, botanists at FDACS-DPI, provided information on the occurrence and cultivation of conifers in Florida and on epicuticular wax. Thanks are extended to Ben Normark, Dug Miller, John Davidson, and referees for their reviews. Voucher specimens are deposited with the Florida State Collection of Arthropods (FSCA), Coccoidea Slide Collection. This is contribution no. 1294 from the Bureau of Entomology, Nematology and Plant Pathology-Entomology Section.