Lobate Lac Scale Introduction, Impact and Potential Harm

The lobate lac scale, Paratachardina lobata lobata (Chamberlin), was first detected in southern Florida in 1999 (Hamon 2001), in Davie in Broward County (Division of Plant Industry [DPI], Florida Dept. of Agricultural and Consumer Services, collection record). During the spring and summer of 2002, the insect developed alarming densities on many host plants in Broward County. In a sample of a residential yard (0.33 acre = 0.135 hectare) in Ft. Lauderdale during August 2002, the scale was found to attack 55% (37/67) of the woody plant species present in 19 of 30 (63%) of the families (Pemberton, unpublished data). Preliminary surveys of natural areas in Broward and Miami-Dade Counties indicate high levels of attack on native plants. At Secret Woods Nature Center in Broward, the scale infests more than half of the tree and shrub species, and more than half of the individual plants examined (Pemberton, 2003). Many of the most important parks and preserves in southern Florida have been invaded, including: Everglades National Park, Big Cypress National Wildlife Refuge and Loxahatchee National Wildlife Refuge. Wax myrtle (Myrica cerifera L.), red bay (Persea borbonia (L.) Spreng.), coco plum (Chrysobalanus icaco L.), myrsine (Rapanea punctata (Lam.) Lundell), important ecological dominants of mesic habitats, and wild coffee (Psychotria nervosa Swartz), a dominant understory shrub in tropical hardwood hammock forest, are being killed in many localities. Coco plums and wax myrtles are important landscape plants in the region. Tropical fruits including avocado, grapefruit, mango, carambola (Averrhoa carambola L.), atemoya (Annona cherimoya Mill. × A. squamosa L.), sugar apple (A. squamosa), and other less important species are known hosts of the scale. Of these, carambola is the most severely damaged. Two of the most important invasive weeds in southern Florida, melaleuca (Melaleuca quinquenervia S.T. Blake) and Brazilian pepper Schinus terebinthifolius Haddi), are hosts of the scale, and the heavily infested large stands of melalecua appear to generate large numbers of the pest which then infest other plants. Thus far, the scale has been found infesting more than 200 plant species in 55 families in south Florida (Howard et al. 2002; Pemberton, unpublished data). Its negative effects will grow as it increases in abundance and spreads to new areas. The scale has also been recorded in the Bahamas (Hamon 2001). This insect could become a threat to cultivated and native vegetation in the West Indies and Mexico as well as the subtropical regions of Texas, California, and Hawaii.

Taxonomy and Identification

Specimens of a new lac scale found in southern Florida in 1999 were determined to be Paratachardina lobata lobata by Avas Hamon, Florida Division of Plant Industry (Hamon 2001) and confirmed by D. R. Miller, USDA-ARS-Systematic Entomology Laboratory. Many subsequent collections have been determined to be P. lobata lobata. This species first appeared in the literature in 1922, when E. E. Green published a detailed description and drawings of material from Sri Lanka. Green (1922) believed this insect to be conspecific with Tachardia minuta Morrison from the Philippines. Chamberlin (1923) recognized that the lobate scale from Sri Lanka was distinct and described it as the new species, Tachardina lobata (Chamberlin), based on a name used earlier by Green. The genus Paratachardina was separated from Tachardina by Balachowsky in 1950, but the new combination Paratachardina lobata was not published until 1976 (Varshney 1976a). The description of two subspecific taxa, P. lobata var. schmidtii (Madhihassen) and P. lobata var. walczuchii (Madhihassen) from India by Madhihassen (1946) resulted in a subspecific designation of P. lobata lobata. These subspecific separations were based primarily on differences in host plants from which the scales were collected, which is insufficient given the polyphagous nature of the species (R. K. Varshney, pers. comm.). Our Florida lobate lac scale appears to be similar to Green’s drawings of the scale that became P. lobata lobata.

The lac scale family Kerridae is widely distributed in warmer parts of the New and Old World including Australia (Varshney 1976a). Paratachardina is in the subfamily Tachardininae with the genera Afrotachardina and Tachardina. The other subfamily in the family is the Tachardiinae, which contains Austrotachardina, Kerria (genus of the true lac scales), Metatachardina, Tachardiella, and Austrotachardiella. Paratachardina species are limited to the Old World, whereas Austrotachardiella and Tachardella (Tachardiinae) are the only New World genera in the family. Scales in the Tachardininae have horny testae, compared to testae composed of alcohol soluble resin in scales of the better known Kerria species and other members of the subfamily Tachardiinae. There are seven kerriid species in western United States, all in the genus Tachardiella, and a single Austrotachardiella species in Jamaica (Miller & Ben Dov 2002).

Native Range of the Lobate Lac Scale

The native range of the lobate lac scale, as defined in the literature, is Sri Lanka and the three southern states of India, below about 16 degrees north latitude. Recorded localities include the type localities of Peradeniya and Kandy in Sri Lanka, and Indian localities of Coimbatore in Tamil Nadu and Bangalore in Karnataka (Green 1922). Additional localities include Cuddapath in Andhra Pradesh (Ayyar 1930) and Calcutta in West Bengal (Varshney 1976a). The Calcutta locality, which is at nearly 23 degrees north latitude, is questionable because the scales from this collection were abnormal due to being parasitized which made their identification uncertain (R. K. Varshney, pers. comm.). Few specimens of the lobate lac scale exist in collections. The USNM has a single specimen, which is a paratype of Green’s type material deposited at the University of California at Davis (D. R. Miller, pers. comm.). The Natural History Museum in London has no material (J. Martin, pers. comm.) and the scale is unlikely to be represented in Indian collections (Varshney, pers. comm.). I saw no material at the Indian Lac Scale Institute in Ranchi, Jarkhand during a September 2002 visit. A native distribution limited to southern India and Sri Lanka below 16 degrees north latitude is surprising given the scale’s ability to thrive in southern Florida at about 26 degrees north latitude. Why it doesn’t occur farther north in India is unclear. Perhaps the limited collection records do not adequately define the native distribution.

Host Plants of Lobate Lac Scale in its Native Range

The lobate scale was described from material collected from Flacourtia (Flacourtiacae) and Fluggea (Fabaceae) (Green 1922). The scale is known to be polyphagous and Varshney (1992) lists species in 42 genera of woody plants, in 25 families, as hosts, including: Annona, Aralia, Acalypha, Averrhoa, Bauhinia, Cryptostegia, Casuarina, Coffea, Celastrus, Citrus, Cestrum, Dodonaea, Erythroxylum, Ficus, Graptophyllum, Guazuma, Gymnosporia, Hibiscus, Hamelia, Kigelia, Loranthus, Lagerstroemia, Mangifera, Mallotus, Michelia, Malpighia, Pongamia, Pyrus, Punica, Phyllanthus, Semecarpus, Spondias, Stererospermum, Spathodea, Securinega, Sesbania, Santalum, Sterculia, Terminalia, and Thespesia. The genera in bold have been recorded as host species in southern Florida (Howard et al. 2002; Pemberton, unpublished data).

Need for Biological Control

Biological control offers a much needed solution to the lobate lac scale problem. No parasitism has been detected in the lobate lac scale populations in Florida. To attempt to detect parasitism, 3,000 mature female scales, collected on the twigs of 15 host plants (10 native plants and 5 non-native plants) in 7 localities (urban developed areas and nature preserves), were examined with a dissecting microscope for parasitoid emergence holes (Table 1). Three scales had possible parasitoid emergence holes. Dissections of these three scales found no evidence of parasitism (larval head capsules). During the process of examining and counting the 3,000 scales, large numbers of uncounted scales of various ages and sizes were scanned because the scales were in dense aggregations on the collected twigs. No emergence holes were noted in the uncounted scales.

Intensive use of insecticides to control this scale is problematic because of the cost to treat the large residential and natural areas infested, and the potential for environmental damage. Many scale insects have been successfully controlled by biological control, including the Florida red scale, Chrysomphalus aonidum (L.), formerly a pest in Florida (Kennett et al. 1999).

Recorded Predators of Lac scale, Kerria lacca (Kerr) in India

Little is known about the predators of lobate lac scale. By contrast, the predators and other natural enemies of commercial lac scale, Kerria lacca (Kerr) in India are better known, and the most important species are relatively well studied. The most important invertebrate predators of the commercial K. lacca are predatory Lepidoptera (primarily Eublema amabilis Moore (Noctuidae) and Pseudohypatopa (= Holcocera) pulvera Meyr; (Blastobasidae), followed by lacewings (Chrysopa spp., Chrysopidae: Neuroptera) (Narayanan 1962). The predators causing the greatest mortality of K. lacca are E. amabilis and P. pulvera, which can destroy 35-40% of a lac crop (Malhotra & Katiyar 1975 cited by Sharma & Jaiswal 2002). Their larvae feed on the scales from silken tubes and consume between 40 and 60 scales during their development. The Chrysopa spp. are sporadic pests that sometimes cause significant morality (Sharma & Jaiswal 2002). The important predators of K. lacca are thought not to be limited to lac scales in their range of prey (Sharma & Bhattacharya, pers. comm.). Less important predators include many moths and lacewings (Narayanan 1962), a cucujid, a tenebrionid, a mycetophagid, several blattellids (Bhattacharya 2002), as well as an assortment of coccinellids and other insects (Sharma et al., unpublished data). Coccinellids may be worth investigating because many species are scale specialists (Hodek 1973). The earliest and perhaps best known example of insect biological control involved the vedalia beetle, Rodolia cardinalis (Mulsant) on the cottony cushion scale (Icerya purchasi Maskell) in California during the late 1800s (DeBach 1974). A scale-feeding coccinellid (Cryptognatha nodiceps Marshall) successfully controlled the coconut scale (Aspidiotus destructor Signoret) in Fiji (Sweetman 1936), but coccinellids can have difficulty in successfully controlling some scales with hard coverings, such as many Diaspididae (Clausen 1940). This suggests that coccinellids might have difficulty controlling the lobate lac scale which has a very hard testa.

Recorded Parasitoids of Lac Scales (Kerriidae)

Varshney (1976b) lists and discusses 28 parasitoids recorded from lac scale species worldwide. The four braconid wasps listed are erroneously recorded as lac scale parasitoids and are actually parasitoids of some of the many predacious Lepidoptera that attack lac scales (Editor V. K. Gupta’s note in Varshney 1976b). The remaining 24 species are all chalcidoid wasps (Aphelinidae, Encyrtidae, Eulophidae, Eupelmidae and Pteromalidae). Most (16) of these have been recorded from the commercial lac scale in India. The nine parasitoids which regularly attack the commercial lac scale (Narayanan 1962) are listed in Table 2.

The parasitoids of lobate lac scale have not been sought nor studied, but three species, Tachardiaephagus tachardiae Howard (Encyrtidae), Tetrastichus purpureus Cameron (Eulophidae), and Marietta leopardina Nietner (Aphelinidae), are reported to attack it (Varshney 1976b). Tetrastichus purpureus is a primary parasitoid of lac scales and a hyperparasitoid of chalicidoid primary parasitoids of lac scales. Marietta leopardina also is probably a hyperparasitoid of chalcidoids attacking lac scale, as is another parasitoid, Marietta javensis Howard, commonly reared from commercial lac (Narayanan 1962). Riek (1970) observed that Marietta species are hyperparasitoids. Tachardiaephagus tachardiae and two other parasitoids commonly associated with the commercial lac scale, Tachardiaephagus somervilli Madhihassen (Encyrtidae) and Coccophagus tschirchii Madhihassen (Eulophidae), are not known to be hyperparasitoids nor have alternative hosts (Narayanan 1962). The latter two species also may have the ability to parasitize the lobate lac scale.

Parasitoid Biology, Abundance, and Impact on Commercial Lac Scale in India

Lac scale parasitoids are well adapted to their hard-bodied hosts. The wasps lay one or more eggs through the anal tubercular opening on top of the testa, and either oviposit on or in the body of the scale, depending on the parasitoid species (Narayanan 1962). Superparasitism can occur but typically one parasitoid larva occurs in a single scale (Narayanan 1962). The parasitoids have life cycles of about one month in length, compared to 4-9 months, depending on the scale strain and season, for K. lacca (Narayanan 1962). The parasitoids can therefore have many generations within a particular scale colony, attacking older stages as the scale colony matures.

Of the regularly occurring parasitoids, Tachardiaephagus tachardiae and Tetrastichus purpureus are the most abundant (Bhattacharya 2002). Tachardiaephagus tachardiae, Tetrastichus purpureus, and C. tschirchii have 10-12 generations on commercial lac each year, compared to 9 generations for Paraechthrodryinus clavicornis Cameron, an encyrtid that can be either a primary or secondary parasitoid (Narayanan 1962). The level of parasitism, measured for the regularly occurring parasitoid complex for seven years from 1928 to 1935, was only 4.8%, but in certain localities and seasons the parasitism level could be as high as 50% (Narayanan 1962). Chauhan (1984 cited in Sharma & Jaiswal 2002) reinterpreted these data and reported that parasitism of the relatively more important females was between 20-37%. Parasitized scales are consumed in large numbers by predatory Lepidoptera larvae, primarily E. amabilis and H. pulvera, which are the major pests of lac scale culture. After cultural methods were developed to reduce the abundance of these lac scale predators, the average parasitism level jumped to about 30% (Bhattacharya, pers. comm.). This level occurs despite the abundant and persistent hyperparasitoids which presumably kill many primary parasitoids.

Recorded Pathogens of Commercial Lac Scale in India

Sharma & Jaiswal (2002) reviewed the literature on diseases of lac scale. Most of the organisms involved are fungi and these are primarily black molds, such as species of Capnodium, Fumago, and other species that grow on the honeydew secreted by the scales. These fungi can cause losses in lac yield because their growth inhibits the respiration, mating, larval emergence, and efficient use of the plant by the scale. A Pythium sp. is reported to cause heavy mortality of the larvae, which fail to complete development (Misra 1928 cited in Sharma & Jaiswal 2002).

Biological Control Approaches for the Lobate Lac Scale

Several biological control approaches to acquire natural enemies appear feasible. Because the natural enemies of lobate lac scale have been neither sought nor studied, explorations for its natural enemies should be made in its native range. The Biological Control Institute in Bangalore has expressed a willingness to provide assistance in such a research project (J. Rabindra, pers. comm.). Bangalore is a locality where the lobate lac scale has been collected so would be a good base to conduct surveys. It is not known how common the lobate lac scale is within its native range. Green (1922) indicated that he had known the species for more than 20 years, suggesting that it might be common at least in parts of Sri Lanka. For this reason, surveys should be made in Sri Lanka as well as in southern India. Baiting for parasitoids and other natural enemies, with scale cultures of a range of age-size classes, in lobate lac scale’s native range could be informative and profitable, especially if the lobate lac scale is uncommon or has a patchy distribution.

Another approach would be to examine the potential of using parasitoids of commercial lac scale for the control of lobate lac scale. Some, including Tachardiaephagus tachardiae, are known to attack lobate lac scale and others may have the potential to use the scale. In September 2002, I visited the Indian Lac Institute in Ranchi, Jarkhand, India, and R. K. Varshney in Aligarh, Uttar Pradesh, India, to investigate the possibilities of using the parasitoids of the commercial lac scale for the biological control of lobate lac scale. The Indian Lac Institute was established in 1926 to conduct research on lac scale cultivation and lac scale products which include resin, waxes, dyes and other chemicals. Lac cultivation is an ancient agricultural activity and cottage industry in India, that was mentioned in the Hindu Vedas more than 2,000 years ago (Mukhopadhay & Muthana 1962). Income from lac is an important subsidiary income for farmers and forest-dwelling peoples in Bihar, Jarkhand, Orrissa and other areas of India (Mukhopadhay & Muthana 1962).

Scientists at the Indian Lac Institute are intimately familiar with lac scale cultivation and maintain lac scale cultures for research purposes, including research on the pests of lac scale. They have the capability to collect desired parasitoids that emerge from their cultures and ship them to a Florida quarantine laboratory. Adults of lac scale parasitoids are apparently short-lived (A. Bhattacharya, pers. comm.) but, if fed with honey, they might live long enough to be successfully shipped to Florida. The Lac Institute also has the capability to provide lac scale parasitized with desired parasitoid species. To do this, they could rear parasitoids of interest from their lac scale cultures, and induce these to parasitize clean (unexposed) even-aged cultures of the lac scale. The parasitized lac scale could be protected from additional parasitism by unwanted species and maintained for several weeks to allow for parasitoid development, and then shipped to Florida quarantine prior to adult parasitoid emergence. Because the temporal life cycles of lac scale strains are well known, it would be possible to induce parasitism in cultures of large recently mated female scales that are months away from producing crawlers. After parasitoid emergence and transfer to lobate lac scale cultures in the Florida quarantine laboratory, the lac scale hosts could be destroyed prior to crawler emergence. Advantages of obtaining parasitoids from lac scale cultures at the Lac Institute would include the following: (a.) known, desired parasitoid species could be obtained in sufficient numbers; (b.) these should have few if any hyperparasitoids; and (c.) the potential risk related to large numbers of small crawlers associated with the commercial lac hosts could be avoided. Because the lac scale is quite polyphagous (Varshney 1992), its regularly occurring parasitoids probably have the ability to locate the scale on very diverse host plants. This behavioral trait should give these parasitoids the ability to locate lobate lac scale on its diverse plant hosts in Florida. Tachardiaephagus tachardiae is the parasitoid of most interest because it is known to be able to attack the lobate lac scale. Two other parasitoids, Tachardiaephagus somervilli and C. tschirchii, should be tested as well. They are not recorded to parasitize lobate lac scale, but the absence of recorded parasitism may reflect the lack of parasitoid rearing on the lobate lac scale. Most of the research on lac scale predators and parasitoids has been done north of the apparent native range of the lobate lac scale in India. The commonness of these parasitoids, despite the presence of predators and hyperparasitoids, suggests the capacity to develop large populations when freed of these enemies. This could make them valuable in lobate lac scale control in Florida. These parasitoids should also be able to establish and thrive in the climatic conditions of southern Florida because the climates of Ranchi, Jarkhand and southern Florida are similar. Ranchi is located at 24 degrees N. latitude and 600 meters above sea level, compared to Miami at 26 degrees N. near sea level. Both areas have cool dry winters, hot rainy summers, and infrequent frosts.

Safety Considerations of Lobate Lac Scale Biological Control

The adoption of nontarget native insects by introduced biological control insects has been increasingly documented in recent times (Louda et al. 2003). The potential host range of candidate biological control insects should be predicted prior to their release to lessen the risk to native insects and introduced insects of value (Strong & Pemberton 2000). This can be accomplished by an evaluation of the well-known taxonomically limited prey specialization of some natural enemy taxa, and host-specificity testing research. Host-specificity testing of parasitoids has been shown to be a good predictor of field host range (Barratt et al. 2000) and is recommended for candidate biological control agents of the lobate lac scale. Risk to nontarget insects depends on how closely related the potentially exposed, valued insect fauna is to the lobate lac scale, and the degree of specificity of the natural enemies employed against the lobate lac scale. There are no native species of the lac scale family (Kerriidae) in Florida and, as mentioned above, only seven kerriids occur in the United States and these are confined to the arid Southwest which would probably preclude both exposure and adoption by parasitoids introduced to Florida. Neither the genus Paratachardina nor the subfamily to which it belongs (the Tachardininae) occur in the New World (Varshney 1976a), so there are no closely related scales in the region. The closest family members are Tachardiella species in Texas and Mexico and a single Austrotachardiella species in Jamaica (Miller & Ben Dov 2002). Testing of some species in these genera should be considered, although obtaining and/or culturing them could be difficult. Representative species of the 13 native scale families (superfamily Coccoidea) in Florida also should be tested. These families are the Aclerdidae, Asterolecaniidae, Cerococcidae, Coccidae, Conchaspidae, Dactylopidae, Diaspididae, Eriococcidae, Kermesidae, Lecanodiaspididae, Margarodidae, Ortheziidae, and Pseudococcidae (derived from Miller and Ben Dov in 2002 by F. W. Howard). The inadvertent reduction of native scale populations by introduced natural enemies might have consequences far beyond the scales affected. Dactylopius scales illustrate the point. Dactylopius species have been successfully used in many parts of the world to control exotic weedy prickly pear cacti (Opuntia species) (Julien & Griffiths 1998). This suggests that Dactylopius species play a role in regulating their host Opuntia in their native areas, such as in Florida. Reduction of Dactylopius scales could reduce or eliminate their regulatory effects, which could allow some host Opuntia species to become unnaturally abundant. One Florida species, Opuntia stricta (Haworth) Haworth, has been a severe weed in many parts of the world (Julien & Griffiths 1998), where it has been introduced and without its natural enemies. Representatives of other hemipteran families, particularly those that have species with sessile or sedentary nymphs, should be tested. This includes: the recently introduced psyllid Boreioglycaspis melaluecae Moore, a promising biological control agent of Melaleuca quinquenervia (Cav.) S.T. Blake; Calophya spp. (Psyllidae) Similarly Hemiptera being evaluated as potential biological control agents of Brazilian pepper and strawberry guava (Psidium cattleianum Sabine) in Florida should be tested. These include and Tectoccocus ovatus Hempel (Eriococcidae) respectively (J. P. Cuda, pers. comm.). Although it is desirable to avoid nontarget use of native insects, the potential adoption of some native insects as hosts should not in my opinion automatically exclude the introduction of a promising natural enemy. The potential risk to native and valued insects needs to be evaluated in relation to the potential benefit gained by control of lobate lac scale, which is a great threat to native and economic vegetation in Florida and elsewhere where it is likely to spread. It should be possible, however, to find and employ natural enemies with narrow enough host ranges to minimize the risk to nontarget species. Parasitoids will probably be safer agents than predators.

A cooperative biological control effort against the lobate lac has been developed. Participants at this point include this author, R. W. Pemberton (USDA-ARS), R. Nguyen (Division of Plant Industry, Bureau of Methods and Biological Control, Gainesville, Florida), F. W. Howard (University of Florida, IFAS, Davie), Florida, and Indian cooperators at the Indian Lac Institute and Biological Control Institute in Bangalore.