Both mealybugs (Hemiptera: Pseudococcidae) and armored scales (Hemiptera: Diaspididae) are regarded as serious phytophagous pests of orchids (Asparagales: Orchidaceae) grown in cultivation (Cullina 2004). By removing nutrients with their piercing-sucking mouthparts, these insects can reduce plant vigor and cause plant death (McKenzie 1967; Kosztarab 1990). Mealybugs, in particular, also secrete copious quantities of honeydew that serve as a food source for ants and sooty mold, the latter of which hinders photosynthesis by coating leaf surfaces (Wood et al. 1988). Scales and mealybugs are often difficult to detect due to their small size and habit of concealment beneath leaf sheaths and crevices. Moreover, the diminutive size of the immature motile stages (crawlers) often leaves infestations of new plants undetected, resulting in the rapid spread of new colonies. For plants in cultivation, control of mealybug populations, in particular, often require the use of systemic insecticides, as contact pesticides may fail to reach mealybugs protected by their location on the plant, such as beneath tightly adhered leaf sheaths. Armored scales are even more difficult to control with chemical means because they are physically protected from contact applications by their cover, although Cating et al. (2010) found that the use of Silwet® L-77 plus petroleum oil can suppress scale populations on orchids in cultivation. The efficacy of systemic insecticides, which travel through the vascular system, is limited because armored scales feed by puncturing individual cells and not within the vascular system (Miller & Davidson 2005).

Other than the damage that mealybugs and scales cause to orchids in cultivation, these insects now pose a direct threat to rare native Florida orchids in situ as revealed by 2 recent studies (Ray et al. 2012; Zettler et al. 2012). Zettler et al. (2012) reported mealybugs (Ferrisia sp.) on inflorescences of the state-endangered ghost orchid, Dendrophylax lindenii (Lindl.) Benth. ex Rolfe, in Collier County in 2009 and Boisduval scale (Diaspis boisduvalii Signoret) on other epiphytic orchids in the Florida Panther National Wildlife Refuge in 2010. In 2011, Ray et al. (2012) documented that D. boisduvalii was more widespread and could be found in several orchid populations in both the Florida Panther National Wildlife Refuge and Fakahatchee Strand State Preserve. As an exotic species native to Neotropical regions (Balachowsky 1954; Espinosa et al. 2009), D. boisduvalii adds an additional burden to land managers already faced with the task of protecting native orchids from environmental degradation and poaching. During a return visit to the Fakahatchee Strand in 2012, we encountered another Neotropical greenhouse pest, the orchid mealybug, Pseudococcus microcirculus McKenzie (J.A. Zettler, unpublished data), on a leaf of a clamshell orchid, Prosthechea cochleata (L.) W. E. Higgins. This specimen was collected in close proximity to reintroduced cigar orchid seedlings (Cyrtopodium punctatum [L.] Lindl.) released as a part of a conservation program. Thus, the presence of both phytophagous pests (D. boisduvalii and P. microcirculus) in the most diverse orchid region in North America (Collier County, Florida) is of considerable concern.

In this paper, we provide an update on D. boisduvalii infestations at four sites within the Florida Panther National Wildlife Refuge in 2013, and we document the prevalence of P. microcirculus on native Florida epiphytic orchids. To our knowledge, this is the first published report that documents P. microcirculus on orchids in situ.

Materials and Methods

Results

Of 322 orchids surveyed, D. boisduvalii occurred on 22.7%, P. microcirculus on 9.6%, and 8 (2.5%) had both mealybugs and scales (Table 1). Juvenile orchids were especially susceptible to infestation with 33.3% (18/54) of specimens surveyed having either scales or mealybugs. Of 7 orchid species surveyed, we recorded no scales or mealybugs for only H. porrecta, a leafless species. Mealybugs and scales were present at all 4 sites; however, which species were in association with a given host was not consistent. For example, no mealybugs or scales were found on either E. nocturnum or E. rigidum at North Fritz and West Hinson Lake, but at those sites other orchid species were infested (Table 1). Moreover, these orchid species at McBride's Pond and Cochran Lake had either or both D. boisduvalii and P. microcirculus. Pseudococcus microcirculus occurred on 15.2% of P. cochleata individuals, whereas D. boisduvalii occurred at the highest rates on E. tampensis (54.5%) and E. amphistomum (37.1%). At McBride's Pond, only 1 species (P. concreta) appeared free of scales, but 1 plant in that population did harbor mealybugs. Although D. boisduvalii was found on leaves, stems, and capsules of its host, these insects were most commonly observed clustered in protected areas near the leaf midrib or under the leaf sheath. Mealybugs were also concealed and were primarily found at the base of each plant hidden within the roots and beneath pseudobulb sheaths. In addition, mealybugs were nearly always associated with newly-formed leaf shoots (Fig. 1). For these plants, small groups of 2–20 mealybugs were typically located near the base of new leaf shoots. In rare instances, mealybugs were found on exposed surfaces such as inflorescences (Fig. 1).

Discussion

Past surveys of these orchid populations showed a trend to increasing scale levels despite differences in sample sizes. In 2011, 1,726 orchids were surveyed with an incidence of 39 with scales (2.3%) and no mealybugs being apparent (Ray et al. 2012). In 2012, 503 orchids were surveyed with an incidence of 39 with scales (7.7%; L.W. Zettler, unpublished data). In this study, we found that 22.7% of orchids had D. boisduvalii. Although other scale species were found at these sites in a previous study (Zettler et al. 2012), only D. boisduvalii and P. microcirculus were present in this study. Why fluctuations may occur from year to year is unknown but could be linked to a combination of biotic and abiotic factors. For example, Collier County, Florida, experienced a prolonged drought during 2009–2012, but the Naples area received above average rainfall in 2013 ( www.nws.noaa.gov). Cockfield & Potter (1986) suggested that armored scale populations decrease when their host plants are water stressed. Thus, the increase in annual precipitation during 2013 might explain the higher incidence of scales in that year. In addition, their populations might be naturally cyclic because of natural biological control agents, as previously documented by Ray et al. (2012). Parasitoids tentatively assignable to Aphelinidae, Encyrtideae, and Signiphoridae were reared from D. boisduvalii colonies collected in 2012 and 2013 (Zettler & Zettler 2013; J. A. Zettler unpublished data).

Table 1.

A compilation of Boisduval scale (Diaspis boisduvalii) and orchid mealybugs (Pseudococcus microcirculus) found on six orchid taxa at four sites surveyed in June 2013 in the Florida Panther National Wildlife Refuge (Collier, Co. Florida). The numbers in parentheses represent the percentage of individual plants infested.

Fig. 1.

(a) Debris deposited by ants around the base of Prosthechea cochleata where orchid mealybugs were concealed; (b) removal of an orchid leaf sheath on a new shoot reveals a large population of mealybugs on P. cochleata; and (c) 2 orchid mealybugs on the inflorescence of Polystachya concreta.

The orchid mealybug, P. microcirculus, was described in 1960 from specimens collected from orchids from several nurseries in California (McKenzie 1960). In 1962, P. microcirculus became the target of eradication efforts in California, and nurseries with infestations were quarantined (McKenzie 1967). Miller et al. (2005) regarded P. microcirculus as only a minor threat to U.S. agriculture because the principle hosts are orchids. To date, no published records have documented P. microcirculus on orchids in a natural environment in either California or Florida. In an artificial setting (greenhouses), mealybugs typically remain hidden among roots and planting media and are apparent on the upper plant parts only when populations attain high densities (McKenzie 1967). On orchids, mealybugs typically congregate beneath the leaf sheaths, at the bases of leaf petioles, and occasionally on the underside of the leaves, affording these pests protection from predators and contact insecticides (McKenzie 1967). As a result, early eradication efforts were not successful, and P. microcirculus remains a pest in greenhouses in California (Johnson 2009). Given that P. microcirculus appears to exhibit the same cryptic feeding behavior on orchids in the natural setting, land managers charged with the task of controlling this pest in situ may experience the same set of challenges currently faced by orchid growers.

Mealybugs feed on the phloem of their host and secrete honeydew waste that supports the growth of saprophytic fungi (sooty mold) capable of coating the leaves and reducing photosynthesis. Honeydew production also attracts ants whose tending might lead to increases in the mealybug populations (Daane et al. 2007). During our sampling, we found that the presence of ants or their debris was a reliable indicator that mealybugs were present (Fig. 1), and they could then be located by sorting through old leaf sheaths near new growth. Wheeler (1910) described an ant behavior in which foragers will cover the sticky substance with sand and other debris when they come into contact with a liquid that they cannot otherwise remove. Accordingly, researchers and land managers should look for signs of ant associations as a means of assessing the presence of mealybugs on orchids.

Over the next decade, plant conservationists plan to cultivate Florida's native epiphytic orchids from seed in vitro and reintroduce the greenhouse-grown seedlings into Collier County conservation lands. Considering that greenhouses are known to harbor scales, mealybugs, and other serious orchid pests (e.g., mites), the movement of seedlings from greenhouse to field sites has the potential to exacerbate the spread of orchid pests into natural areas unless preventative measures are devised. Greenhouse managers need to be diligent about inspecting and choosing pest-free sites where laboratory-grown orchids will be cultivated. We are currently characterizing the genetic structure of populations of orchid mealybugs found within the Big Cypress Basin eco-region with microsatellite markers, and we hope that this information might indicate how the spread of these populations can be prevented and controlled.