The Cycad Scale, Aulacaspis yasumatsui Takagi

Fri Oct 11, 2013

by Rafique Bailey

Ph D Entomology

There is an alien species lurking inside our Botanic Gardens and across our landscape. Has anyone noticed? Well, if you haven’t, take another look, it is cycad aulacaspis scale (CAS), Aulacaspis yasumatsui Takagi (Figure 1), an invasive species of scale insects native to South East Asia, which made its way to the US in 1996 and from there has spread to many different countries, including the Caribbean countries of Puerto Rico, US Virgin Islands, Barbados and now St. Vincent. It has also established itself in the Central American countries of Panama, Costa Rica and El Salvador. Cycad Aulacaspis Scale is the major pest of cycads (Cycadacea: Cycadales) (Figure 2). The cycads are gymnosperms and they are thought to be as old as the dinosaurs. Although once abundant around the earth, cycads are now greatly reduced in both numbers and distribution, comprising 11 genera and about 250 species in tropical and subtropical regions in the world (Hill and Vatcharakorn, 1998).{{more}} In appearance, cycads resemble palms or tree-ferns and some species are commonly called sago palms. In St Vincent, CAS was first detected on one plant (Figure 3) at Arnos Vale in March 2012 (Personal Observation). Subsequently, it was found infesting cycads which are found in the Botanic Gardens of St Vincent. It has also been detected on cycads in and around the Kingstown area, however, it has not been seen on cycads on Bequia (Personal Observation).

Invasive Alien Species (IAS) are organisms whose introduction and/or spread impacts human health and well being; disrupts trade and threaten biological diversity (CIASNET.org). In St Vincent, the discovery of Cycad Aulacaspis Scale, the Citrus Psyllid, Black Sigatoka, Lion Fish, Mango Seed Weevil, West Indian Fruit Fly, Red Palm Mite and the Pink Hibiscus Mealy Bug are examples of some of the more recent invasions of foreign species into our ecosystem. What are the economic costs of having these pests? As we are already aware, the government is spending millions of dollars every year for the control of Black Sigatoka in Bananas and Plantains. The export of agricultural products to regional and international markets would also be severely hampered by the presence of these pests. Globally, the cost of damage caused by invasive species has been estimated to be US$1.5 trillion per year, close to 5 per cent of global GDP (CABI, 2013). Globalization through increased trade, transport, travel and tourism will inevitably increase the intentional or accidental introduction of organisms to new environments, and it is widely predicted that the threat posed by invasive species will be further increased by climate change (CABI, 2013).

Management of Cycad Scale

For the management of the cycad scale, Aulacaspis yasumatsui Takagi (Hemiptera: Diaspididae) on Cycas, it is important to collect ecological data of the pest A. yasumatsui as well as its natural enemies; especially a comprehensive life table study, for a thorough understanding of development, survival and fecundity on their hosts. In this regard, Bailey et al., (2010) studied the lifetable of A. yasumatsui, reared on Cycas in Taiwan and elucidated the development, survival and fecundity at 24°C, 70 ± 10% RH, and a photoperiod of 12:12 (L:D) hunder laboratory conditions. We determined that the total pre-oviposition period (TPOP) was 35.92 d. The maximum longevity of female adults was 67 d and 1 d for males. The intrinsic rate of increase (r) was 0.100 d-1, the finite rate of increase (_) was 1.11 d-1, the net reproduction rate (Ro) was 111.51 offspring /individual, and the mean generation time (T) was 47.24 d.

Four methods have been used to try to suppress the cycad scale population in Florida, with varying degrees of success. They include Chemical Control, Biological Control, Cultural and Mechanical Control, and Integrated Control.

Chemical Control

Montgomery Botanical Garden in Florida has been a leader in testing various chemicals such as the growth regulator, pyriproxyfen (trade name Distance), and the contact/systemic insecticide, dinotefuran (trade name Safari) to effectively control and suppress reproduction of CAS. Although these chemical measures are effective, they are costly. For example, MBC spent USD $2,800.00 to purchase enough dinotefuran for a single application on its cycad collection of 1,043 plants spread over 0.8 hectare of land area. In addition to the chemicals, it took two horticulturists three full days to apply this single treatment. For conservation collections in third world countries, where labor is relatively inexpensive, the cost of chemicals alone may be prohibitive (IUCN/SSC, 2005).

Biological control

Two natural enemies of cycad scale were collected in Thailand by R. M. Baranowski of the University of Florida, Tropical Research and Education Center (TREC) (Baranowski and Glenn, 1999). The beetles were identified as Cybocephalus nipponicus (Endrody-Younga) and the parasitoids as Coccobius fulvus (Compere and Annecke). Approximately 32,675 C. binotatus were released at over 40 locations in South Florida between September 1997 and December 1998 and 15,000 C. fulvus parasitoids were released from February to April 2002 in Brevard, Broward, Dade, Hillsborough, Indian River, Lake Manatee, Martin, Orange, Palm Beach, Pinellas, Saraso and St. Lucia Counties. Beetles and parasitoids have been recovered from most release locations where the plants were not sprayed with insecticides and most plants were free of scale insects (Baranowski and Glenn, 1999). Although both these natural enemies have established there, they seem unable to provide satisfactory control (Cave 2005).

In September 2003, the predatory beetle Cybocephalus nipponicus was imported from Thailand to the quarantine facility at the National Pingtung University, Neipu, Taiwan. C. nipponicus was field released in the Taitung Cycad Nature Reserve in November 2005 and in Pingtung and Taichung in October 2005 (Chao and Lai, 2005). Bailey and Lai (2006), evaluated C. nipponicus under laboratory and field conditions and found that the predator required a low number of cycad scales for C. nipponicus larvae to develop and its adults to reproduce. Bailey and Lai (2006) also discovered a native species of Cybocephalus beetles from Taiwan which was subsequently identified as a new species and named Cybocephalus flavocapits Smith (Smith and Bailey, 2010). Bailey et al., (2011) evaluated Cybocephalus flavocapitis in laboratory and field and determined that the intrinsic rate of increase (r) was 0.05 d-1, the finite rate of increase (_) was 1.05 d-1, the net reproductive rate (R0) was 29.1 offspring, and the mean generation time (T) was 63.3 d. The predation rate of larvae and adults were 743 eggs and 1595 scales, respectively.

The net predation rate for C. flavocapitis is 1874 scales.

In the two wild populations of cycads where CAS has recently invaded, namely C. micronesica in Guam and C. taitungensis in Taiwan, terrain obstacles such as tangled foliage and cliffs has made hand application of insecticides very difficult. Also the huge number of plants, reportedly to be about one and half million of C. micronesca on Guam, would be impossible to treat (IUCN/SSC, 2005).

According to the recommendations of the IUCN/SSC (2005); understanding the biology of any scale insect can lead to cultural practices that may prevent their spread and keep populations at low levels. For example, growers and homeowners should follow proper sanitation practices in pruning infested plants. In many cases, the crawler stage (dissemination life stage) can be spread from plant to plant by pruning equipment or by infested clippings that are not discarded properly. A good practice is to clean pruning equipment before moving to new plants and to destroy infested clippings to eliminate them as potential sources of further infestations.

Growers can also isolate infested plants or blocks of plants away from non-infested plant material. Crawlers are readily disseminated by wind currents and can be blown for great distances to new host plants. The direction of the wind should be considered when isolation is needed. Placement of infested plant material upwind of non-infested plant material can result in infestation of the non-infested plants.

One grower reported good control by pruning all infested fronds. However, the next flush of fronds may become infested from the stem or roots, and successive pruning to control the scale can severely stress the plant.

After chemical application, the scale covers of dead CAS adhere to the foliage, blocking photosynthesis and interfering with the pest controller’s ability to determine if another CAS outbreak is occurring. CAS can be removed from intact cycad foliage by using high pressure water sprays.

Integrated Control

Integrated control, or integrated pest management (IPM), is the combined use of a variety of control measures (chemical, biological, mechanical and cultural) together with exploitation of seasonality, pest behavior, and other factors to achieve a more effective control than any given method can effectively yield alone. For example, Montgomery Botanical Center management plan consists of the following: (1) increase air flow and plant access, (2) regular scouting, (3) horticultural oils, (4) rotation of pyriproxifen (Distance) and dinetuferon and, (5) utilizing parasitic wasps. MBC’s IPM program is a template for others to use (Wiese, 2006).

Integrating Biological, Mechanical and Chemical Control

Applying insecticides can adversely affect biological control agents. Therefore, certain plants within a collection should be set aside as breeding sites for biological control agents and thus, should be excluded from pesticide usage. Preferably, these sites should be large Cycas specimens on which parasites and predators can build large, stable populations (IUCN/SSC, 2005).

Pesticide excluded plants (Sentinel) can be sprayed with high pressure water sprays to keep the level of CAS at low levels while the biological control agents are establishing themselves. Effective biological control has been achieved on semi-isolated cultivated plants in South Florida using this method. In such cases, agents besides insect parasitoid/predators, such as pathogenic fungi to CAS may also be involved. The use of growth regulators or target-specific insecticides that do not adversely affect the predators/parasitoids is another option (IUCN/SSC, 2005).

If acceptable levels of CAS can be achieved with biological control in Sentinel plants, other specimens can be added to the program so that effective biological control is achieved step by step while an ongoing chemical control program continues. While such a gradual introduction program is progressing, it provides an opportunity to conduct in-depth studies of how the biological control agents functioned. Such data may provide crucial insight into accelerating the introduction and establishment of effective biological control organisms to an area suffering from an incipient CAS outbreak (IUCN/SSC, 2005).

Conclusions and Recommendations

Cycad Scale has now established itself on St Vincent and if no action is taken, it would soon wipe out all cycads here. In order to keep populations of the pest to a low level, attention should be paid to all of the different methods of control as outlined above. Integrating biological, mechanical and chemical control whenever possible should be applied to help to combat this pest. Additionally, surveys should be done to identify any possible local natural enemies of cycad scale here. There is currently no biological control programme in St. Vincent for the control of invasive species. A Classical Biological Control programme should therefore be initiated by local authorities for this pest as well as other invasive/exotic species present in St. Vincent. More frequent monitoring of ports of entry and customs should be done by the relevant authorities, random searches of speedboats whenever possible should be carried out by the coastguard. There is currently a lack of education and public awareness about invasive alien species in St Vincent.

The Plant Protection and Quarantine Department of the Ministry of Agriculture and Fisheries needs to embark on a more aggressive educational and public awareness programme. All the new scientific studies suggest that climate change will increase the abundance and diversity of insect pests and diseases and a loss of ecological biodiversity. In face of these challenges, there needs to be a national policy and strategy with clearly define goals and objectives, as the first step in formulating an invasive alien species plan. If embarking on eradication, complete a feasibility plan first and ensure the funding is in place to sustain efforts.

Additionally, St Vincent would have to adopt a climate-smart agriculture policy, which should include the use of resistant-varieties, classical biological control, rescheduling of crop calendars, and the screening of pesticides with novel mode of actions. Clearly, there is no plan for the management of invasive species in the Botanic Gardens; the state of the plants has deteriorated since the initial infestation and some have already been chopped down. It is therefore recommended that all the leaves from plants that have already turned brown and sclerotic be removed and burnt. The MBC plan should then be followed. I am willing to share my expertise on this and can be contacted at rskbailey@hotmail.com.