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Pestiferous Scale Insects on Native Epiphytic Orchids in South Florida: A New Threat Posed by Introduced Species
Jennifer A. Zettler, Lawrence W. Zettler, and Larry W. Richardson

Southeastern Naturalist, Volume 11, Issue 1 (2012): 127–134

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2012 SOUTHEASTERN NATURALIST 11(1):127–134 Pestiferous Scale Insects on Native Epiphytic Orchids in South Florida: A New Threat Posed by Introduced Species Jennifer A. Zettler1,*, Lawrence W. Zettler2, and Larry W. Richardson3 Abstract - Scale insects belong to the superfamily Coccoidea, which includes serious plant pests such as soft scales, armored scales, and mealybugs. In 2009, in a natural habitat surrounded by urban development in Naples, FL, pestiferous scale insects (Coccidae) and mealybugs (Pseudococcidae) were discovered on inflorescences of Dendrophylax lindenii (Ghost Orchid). The next year, a follow-up survey was initiated to also include plants in two orchid-rich habitats within the Florida Panther National Wildlife Refuge. There, exotic scales were found on six different epiphytic orchid taxa. Of the scales encountered, Coccus hesperidum (Brown Soft Scale) and Diaspis boisduvalii (Boisduval Scale) are both well-known and serious pests of cultivated plants. Of particular concern is the possibility that these invasive insects have thoroughly infiltrated isolated, natural habitats of rare native orchids. Introduction About half (106) of all orchids native to North America occur in Florida, and half of these species are confined to the southernmost part of the state (Brown 2005). Here, the rarest epiphytic orchids are found in the Big Cypress Basin eco-region (Collier and Monroe counties) deep within sheltered cypress domes, sloughs, and other freshwater wetlands. Since the 1940s, extensive tracts of land have been purchased by the state and federal government to safeguard South Florida’s unique flora and fauna, but unfortunately, orchid poaching persists, even in seemingly inaccessible habitats nestled in reserves. Like poachers, exotic species are known to infiltrate protected habitats undeterred. Once established, some exotics alter natural ecosystems by outcompeting native plants and animals, and others pose a direct threat to native species by inflicting physical harm (reviewed by Pimentel et al. 2005). As a result, considerable funds are aimed at the eradication or control of invasive species (reviewed by Pimentel et al. 2005). Although epiphytes rarely suffer from leaf defoliation from herbivores (Benzing 1990), orchids are vulnerable to mites (Zhang 2003) and scale insects (Johnson 2010) that damage plants with piercing-sucking mouthparts, causing stippled and pitted leaves and other systemic damage. Such plant injuries are typically prevalent on orchids in cultivation (e.g., greenhouses), and the feeding damage from a single scale insect can make a plant unsalable (Johnson 2010). For example, Diaspis boisduvalii Signoret (Boisduval Scale) is considered the 1Department of Biology, Armstrong Atlantic State University, 11935 Abercorn Street, Savannah, GA 31419. 2Orchid Recovery Program, Department of Biology, Illinois College, 1101 West College Avenue, Jacksonville, IL 62650. 3Florida Panther National Wildlife Refuge, US Fish and Wildlife Service, 3860 Tollgate Boulevard, Suite 300, Naples, FL 34114. *Corresponding author - jennifer.zettler@armstrong.edu. 128 Southeastern Naturalist Vol. 11, No. 1 most important pest of cultivated orchids in Florida (Dekle 1965), probably arriving there on infected plants imported from tropical America, where it is native (Balachowsky 1954). In a greenhouse setting, first instars of immature scales are mobile and can crawl to neighboring, uninfected plants. These crawlers can also utilize wind currents to achieve dispersal (Washburn and Washburn 1984). Little is known, however, about the occurrence of scales and their dispersal mechanisms on orchids in their native habitats. On 24 July 2009, we collected immature soft scales (Pulvinaria sp., Coccidae) and mealybugs (Ferrisia sp., Pseudococcidae) on inflorescences of Dendrophylax lindenii (Lindl.) Benth. ex Rolfe (Ghost Orchid) from an isolated, natural site in Collier County, flsurrounded by an urban area. The scales were tended by ants that were later identified as an exotic species, Pheidole moerens Wheeler (Wandering Big-Headed Ant), native to the Greater Antilles (Deyrup et al. 2000). The following day, Wandering Big-Headed Ants were recovered from two other rare orchids, Epidendrum nocturnum Jacquin (Night-Fragrant Epidendrum) and Polystachya concreta (Jacquin) Garay & Sweet (Helmet Orchid), in a more remote part of the county in the Florida Panther National Wildlife Refuge (FPNWR). These ants were associated with flower buds, developing ovaries, and racemes of orchids in the act of initiating anthesis. The occurrence of these insects from two natural orchid populations prompted the present study. In this paper, we provide a preliminary survey of pestiferous and/or exotic insects collected on native epiphytic orchids inhabiting the FPNWR, and discuss the potential impact that these insects might have on the native orchids in this important eco-region. Study Area On 25 and 26 June 2010, insects were collected from three sites in Collier County, FL: 1) an isolated wetland forest nestled within an urban area (its exact location has been omitted herein to reduce the likelihood of orchid poaching), 2) McBride’s Pond, and 3) Cochran Lake. The latter two sites were within the confines of the 10,683-ha FPNWR, located 32 km east of Naples. The FPNWR was chosen for its remote rural location and the orchid-rich habitats contained therein (Stewart and Richardson 2008). McBride’s Pond and Cochran Lake consisted of frequently flooded cypress domes dominated by Taxodium distichum (L.) L.C. Rich (Bald Cypress). Although extensive (ca. 300 x 200 m), both sites were separated by ca. 1 km of pine flatwoods and wet prairie habitats. The majority of the orchids were affixed to low (1–5 m above the ground) overhanging branches of understory trees, namely Annona glabra L. (Pond Apple) and Fraxinus caroliniana Mill. (Pop Ash), which allowed for sampling by foot. Various growth stages of orchids, including seedlings and juveniles, were commonplace on limbs of the understory trees, especially in association with mosses. Methods Sampling, collecting, and identification Seven species of epiphytic orchids were surveyed for insects: D. lindenii, Encyclia tampensis (Lindley) Small (Florida Butterfly Orchid), Epidendrum 2012 J.A. Zettler, L.W. Zettler, and L.W. Richardson 129 amphistomum A. Richard (Dingy-Flowered Star Orchid), E. nocturnum, E. rigidum Jacquin (Rigid Epidendrum), P. concreta, and Prosthechea cochleata (L.) W.E. Higgins var. triandra (Ames) W.E. Higgins (Florida Clamshell Orchid). All seven taxa are listed as endangered in Florida’s Regulated Plant Index (Coile and Garland 2003). For purposes of identification, scale insects were conventionally collected fresh while still attached to their host plant and not treated with preservative. Any ants tending scales or visiting extrafloral nectaries were also collected and identified. The Museum of Entomology at the Division of Plant Industry (Gainesville, FL) served as the repository for our vouchers of scale insects and mealybugs. Voucher specimens of collected ants were deposited in the arthropod collection at the Archbold Biological Station (Lake Placid, FL). Results and Discussion None of the Ghost Orchid plants (n = 11) harbored insect pests at the urban site, where soft scales (Pulvinaria sp.) and mealybugs (Ferrisia sp.) were collected nearly one year earlier (24 July 2009). Five of these Ghost Orchid plants were in full bloom, and six were undergoing anthesis. After searching for other epiphytic orchids at this location, scales were detected from a mature Rigid Epidendrum specimen, and its leaves were coated with sooty mold. These scales were later identified as Coccus hesperidum L. (Brown Soft Scale), and the sooty mold growth might have been triggered by sugars (honeydew) excreted by these insects. No ants were seen in association with the scales. The following day (26 June 2010), the orchids of the FPNWR were sampled. Among 32 individual orchids examined at McBride’s Pond, Diaspis boisduvalii Signoret (Boisduval Scale) was recovered from one Rigid Epidendrum specimen. Of 49 orchids surveyed at Cochran Lake, three types of scales were discovered on 26 plants. Boisduval Scale was found on four orchid species (E. amphistomum, E. nocturnum, E. rigidum, and P. cochleata; Fig. 1), Asterolecanium epidendri (Bouché) (Orchid Pit Scale), was collected from one Helmet Orchid specimen, and Brown Soft Scale was present on Rigid Epidendrums, Florida Butterfly Orchids, and Florida Clamshell Orchids. Although scales were found primarily on juvenile and mature plants, at least one seedling (Helmet Orchid) was infested. In addition, flatid planthopper nymphs (Flatidae) were collected from two Night- Fragrant Epidendrum seedlings (Fig. 2). Of the orchid taxa harboring scales, heaviest infestations were noted on Florida Clamshell Orchids (9 of 22 or 41%) and Helmet Orchids (9 of 13 or 69%). The host trees in this area, Pop Ash and Ilex cassine L. (Dahoon Holly), were also heavily infested with scale (Figs. 3, 4). On one Florida Clamshell Orchid plant, five Wandering Big-Headed Ants were observed tending Brown Soft Scales. On a Helmet Orchid, scales were tended by four ants identified as Pseudomyrmex simplex F. Smith (Fig. 5), a neotropical ant that is apparently native to Florida (Deyrup et al. 1988). This appears to be the first published report documenting pestiferous insects on South Florida’s native orchids in situ. The presence of soft scales (Pulvinaria sp.) and mealybugs (Ferrisia sp.) on the Ghost Orchid in 2009, coupled 130 Southeastern Naturalist Vol. 11, No. 1 with the recovery of scales on epiphytic orchids at all three sites the following year, suggests that these pests have gained a foothold in the Big Cypress Basin eco-region. Miller and Miller (2003) list 16 established or native Pulvinaria spp., and all are classified as pests. Of these 16 species, 11 are reportedly oligo/ polyphagous, capable of feeding on multiple types of plants. Similarly, Miller et al. (2002) report two introduced species of Ferrisia, both of which are polyphagous pests. Of the three scale species collected (Brown Soft Scale, Orchid Pit Scale, Boisduval Scale), all are exotic. Brown Soft Scale is an Old World polyphagous pest with a cosmopolitan distribution (Miller et al. 2005). The Boisduval and Orchid Pit Scales are both from tropical America (Balachowsky 1954, Stumpf 2000) and commonly infest orchids in cultivation. Direct feeding by scale insects can weaken and kill orchid plants (Johnson 2010), and introduced scale species are of considerable concern (Miller et al. 2005). Moreover, mealybugs, flatid planthoppers, and some scales produce honeydew, which Figure 1. Boisduval Scale on a mature Florida Clamshell Orchid growing in the Florida Panther National Wildlife Refuge in Collier County, FL. 2012 J.A. Zettler, L.W. Zettler, and L.W. Richardson 131 Figure 2. Flatid planthoppers on a Night-Fragrant Epidendrum seedling growing in the Florida Panther National Wildlife Refuge in Collier County, FL. Figure 3. Brown Soft Scale on Dahoon Holly growing in the Florida Panther National Wildlife Refuge. often covers vegetative surfaces and encourages sooty mold growth, which inhibits photosynthesis (Wood et al. 1988). Indeed, Hely et al. (1982) state that sooty molds cause more damage to plants than the scales do by feeding. Based on their problematic track record, it is not unexpected that all three scales were recovered from multiple orchid genera (e.g., Epidendrum spp., Encyclia, Polystachya, and Prosthechea). Of particular concern is that scales were also prevalent on orchid host trees, particularly Pop Ash—an important subcanopy associate of native orchids throughout South Florida. Thus, orchid seedlings affixed to infected host trees would be vulnerable to these insects via first instar 132 Southeastern Naturalist Vol. 11, No. 1 Figure 4. A young Helmet Orchid growing on an infested Pop Ash in the Florida Panther National Wildlife Refuge. The patchy chlorosis of the orchid’s leaves is typical of plants with heavy scale infestations. Figure 5. Pseudomyrmex simplex ants tending Brown Soft Scales on a Helmet Orchid growing in the Florida Panther National Wildlife Refuge in Collier County, FL. 2012 J.A. Zettler, L.W. Zettler, and L.W. Richardson 133 nymphs (crawlers), to sooty mold growth triggered by honeydew release from above, or both. Indeed, one orchid seedling (P. concreta) was found to be infested with scales in such an area (Cochran Lake). The role of the ants (P. moerens and P. simplex) observed tending scales remains unclear. Honeydew-producing insects might actually impart a benefit to the host plant by attracting ants that ward off defoliating herbivores (Compton and Robertson 1988, Messina 1981). Likewise, ants that tend extrafloral nectaries (EFNs) of the orchid, E. denticulatum, deter herbivores on its reproductive structures (Almeida and Figueiredo 2003). Koptur (1992) surveyed plants in the Florida Everglades and reported nine orchid species with EFNs, including Night-Fragrant Epidendrums and Rigid Epidendrums. However, defoliating herbivory is rarely seen in epiphytic orchids (Benzing 1990), and thus ants feeding on honeydew or nectar might be benefiting from the interactions without reciprocation to the plants. Moreover, the presence of scale-tending ants might encourage increases in populations of scales by providing them protection from natural enemies. Although this study is preliminary, it calls attention to exotic insect pests invading remote habitats where rare orchids are afforded legal protection in reserves. Eradicating scales from cultivated orchids requires extensive and long-term control methods that can be costly and ineffective for orchid growers (Johnson 2010). Therefore, large-scale treatment of infested orchids in their native habitats might be impractical or even impossible. With 85% of all imported plants arriving thorough the port of Miami (Frank and McCoy 1995), coupled with increased urbanization in the region, South Florida is a focal point for invasive pest insects. Consequently, these insects might have originated from infected plant material in nearby urbanized areas and/or cultivated fields. Given that first instars of scales are known to utilize wind currents for dispersal (Washburn and Washburn 1984), high winds (e.g., periodic hurricanes) might have played some role in the ability of these pests to infiltrate more remote habitats. More thorough surveys are currently planned for the coming year, including surveys in nearby Fakahatchee Strand State Preserve, as well as studies that investigate yearly fluctuations in insect densities on infected orchids. Acknowledgments We kindly thank Tegan Fugate and Amber Furness (Illinois College) for field assistance, Dr. Mark Deyrup (Archbold Biological Station) for identification of the ants, and Drs. Susan Halbert, Greg Hodges, and Ian Stocks (Division of Plant Industry) for identification of Hemiptera. We also appreciate the feedback provided by Dr. F. William Zettler (University of Florida) and J.J. Sadler (Illinois College). Literature Cited Almeida, A.M., and R.A. Figueiredo. 2003. Ants visit nectaries of Epidendrum denticulatum (Orchidaceae) in a Brazilian rainforest: Effects on herbivory and pollination. Brazilian Journal of Biology 63:551–558. Balachowsky, A.S. 1954. Les Cochenilles Palearctiques de la Tribudes Diaspidini. 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A revision of the pit scale species in the subfamily Asterolecaniidae in North and South America. Ph.D. Dissertation. University of Tennessee, Knoxville, TN. 356 pp. Washburn, J.O., and L. Washburn. 1984. Active dispersal of minute wingless arthropods: Exploitation of boundary-layer velocity gradients. 223:1088–1089. Wood, B.W., W.L. Teders, and C.C. Reilly. 1988. Sooty mold fungus on pecan foliage suppresses light penetration and net photosynthesis. Hortscience 23:851–853. Zhang, Z. 2003. Mites of Greenhouses: Identification, Biology, and Control. CABI Publishing, Cambridge, UK. 240 pp.