Aulacaspis yasumatsui (cycad aulacaspis scale (CAS)) or the Asian cycad scale, is highly damaging to cycads, which include horticulturally important and endangered plant species. The cycad scale is an unusually difficult scale insect to control, forming dense populations and spreading rapidly, with few natural enemies in most localities where it has been introduced. The scale has the potential to spread to new areas via plant movement in the horticulture trade.
All adult female Aulacaspis yasumatsui (cycad aulacaspis scale (CAS)) have a waxy outer covering for the protection of themselves and their eggs (the scale) (Weissling et al. 1999). The scale of mature females of A. yasumatsui are: "white, 1.2-1.6mm long and highly variable in form. They tend to have a pyriform shape with the exuviae at one end, but are often irregularly circular, conforming with leaf veins, adjacent scales and other objects. The ventral scale is extremely thin to incomplete. The scale of the juvenile male is similar to those of other species of Diaspididae, being 0.5-0.6mm long, white and tricarinate, with exuviae at the cephalic end. Scales of males are nearly always more numerous than those of females" (Howard et al. 1999). Adult males are orange-brown, and are similar in appearance to tiny flying midges, with one pair of wings and well-developed legs and antennae (Heu et al. 2003). Adult females are also orange in colour (Weissling et al. 1999).
Infestations of CAS on cycads begin on the undersides of leaflets or at the base of the petiole. As the infestation progresses, scales also infest the upper surfaces of leaflets, the terminal portion of the cycad, the trunk and even roots and seeds/cones (Heu et al. 2003; Weissling et al. 1999; Haynes, pers. comm.). The leaves of infested cycads have a whitewashed or snow-covered appearance due to the numerous white scales. Plants that have been infested for some time will typically have chlorotic, yellow-brown leaves, as the continuous removal of plant sap by the scale will usually result in the death of the leaves (Heu et al. 2003). The scale can eventually form several layers, which include a high proportion of dead as well as live insects. Heavy infestations can consist of up to 3,000 scales per square inch in several layers (Weissling, 1999).
A simple way to tell if a plant has CAS, as opposed to other types of scale, is the speed in which it multiplies and the thickness with which it covers the plant. An infestation usually starts on the petioles near the crown of the plant, and works out from there. The plant will usually be totally covered within a couple of months (Broome, 2004).
A. yasumatsui is native to Southeast Asia (Howard et al. 1999; Muniappan, 2005). According to Dr. Chandrashekara and Dr. A. Viraktamath of the Department of Entomology at the University of Agricultural Sciences in Bangalore, India, CAS has so far not been recorded in India.
It has been introduced more widely in Asia and to North America, the Caribbean, Europe, Pacific islands and South Africa. It has been intercepted at the border in New Zealand and in some European countries.
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
Aulacaspis yasumatsui (cycad aulacaspis scale (CAS)) is found on plants from the gymnosperm order Cycadales, which consists of three families - Cycadaceae (Cycas a genus that contains its preferred host species), Stangeriaceae (Stangeria) and Zamiaceae (8 genera). CAS has been recorded on plants of the following genera: Cycas, Stangeria, Dioon, Encephalartos, Ceratozamia, Macrozamia and Microcycas (Howard et al. 1999; J. Haynes, pers. comm.; W. Tang, pers. comm.). These plants represent a wide variety of geographic origin. At Montgomery Botanical Center in Miami, Florida, the heaviest infestations appeared to be on Cycas and Stangeria eriopus. The threatened king sago (see Cycas revoluta in IUCN Red List of Threatened Species) appears to be more susceptible to CAS than most other species (Heu et al. 2003). The cycad scale infests pinnae, rachides, strobili, stems and roots of these various species of cycads. It is primarily found on the underside of leaves (Howard et al. 1999). In containerised plants, CAS usually aggregates on primary roots (about 10mm in diameter), and singly or in groups of a few on secondary roots (about 2mm in diameter) near the container sides. In the field, CAS has been observed at different depths on primary (3cm in diameter) and secondary roots in groups of a few to several individuals from near the soil surface to a maximum depth of 60cm (Weissling et al. 1999).
The preferred host genus of CAS is Cycas, which is native to Asia, as is A. yasumatsui. This suggests that Cycas may be the original host (Howard et al. 1999). CAS has been identified mainly in the monsoon areas of southeast Asia, and has seldom been found on cycads in rainforest areas. This suggests that the ability of CAS to infest roots may be an adaptation to surviving brush fires, a common occurrence in these monsoon areas (Howard et al. 1999).
In South Africa, CAS has been recently reported from non-native and native cultivated cycad species (Nesamari et al., 2015).
Reproduction Female Aulacaspis yasumatsui (cycad aulacaspis scale (CAS)) can begin laying eggs within 21-35 days of hatching in warmer weather (Hamon, 2000; in IFAS, 2005). Eggs hatch within 8-12 days and some individuals have been observed to develop to second instars within 16 days, and third instars in 28 days. Mature females lay >100 eggs (Howard et al. 1999).
Lifecycle stages Generally, scale insects initially hatch into a “crawler” stage capable of movement. When they find a suitable spot on a plant, they will insert their stylet (straw-like mouthparts) into the plant and begin feeding. Shortly after this, they will begin to create a covering over themselves, and they stay this way until they die. (IFAS, 2005).
Male cycad scales emerge from their scale shortly before death and fly in search of females for mating before they die. Females remain attached to the plant until their death. (Haynes and Marler, 2005). Most female cycad scales do not live longer than 75 days (Howard et al. 1999).
Introduction pathways to new locations Host:Aulacaspis yasumatsui (cycad aulacaspis scale (CAS)) can be transported to new locations by the import of infested cycad plants. There is high potential for CAS to spread in this manner as one or more fecund females hidden in the cycad can easily escape detection (EPPO, 2005). Nursery trade:Aulacaspis yasumatsui (cycad aulacaspis scale (CAS)) can be transported to new locations by the import of infested cycad plants. There is high potential for CAS to spread in this manner as one or more fecund females hidden in the cycad can easily escape detection (EPPO, 2005).
Local dispersal methods Garden escape/garden waste: The crawler stage of Aulacaspis yasumatsui (cycad aulacaspis scale (CAS)) can be spread via garden waste or infected pruning equipment (Hodges et al. 2003). Host (local): On animals:Aulacaspis yasumatsui (cycad aulacaspis scale (CAS)) can spread by "hitchhiking" on people,animals, birds, large insects etc. when in the crawler stage (Heu et al. 2003). On animals (local):Aulacaspis yasumatsui (cycad aulacaspis scale (CAS)) can be carried by the wind when in the crawler stage (Heu et al. 2003) infesting plants more than a mile away (Moore, 2005).
Compiled by IUCN SSC Invasive Species Specialist Group (ISSG)
Aulacaspis yasumatsui (cycad aulacaspis scale (CAS)) threatens both ornamental and wild cycad populations. It spreads rapidly and can cover a large cycad within a number of weeks (Haynes & Marler, 2005). It has been observed to kill 100% of a Cycas revoluta population in cultivation within one year of infestation (Howard et al. 1999).
CAS has the potential to disrupt the horticultural trade in cycads. Cycads are valuable ornamental plants worldwide and the scale detracts from the appearance of plants even after treatment as the dead scales do not readily drop off (Howard et al. 1999). CAS also threatens the survival of several rare and already endangered species conserved in botanical collections (Howard et al. 1999; J. Haynes, pers. comm).
CAS can be easily spread to new locations via the plant trade as one or more fecund females on the plant can easily evade detection. This could threaten native cycad populations in these new locations (Emshousen et al. 2004), as is occurring in Guam where CAS is killing off the native cycad (see Cycas micronesica in IUCN Red List of Threatened Species) at an alarming rate (Haynes & Marler, 2005). It is expected that CAS will spread to other islands in the Caribbean and Micronesia unless strict controls are put in place to restrict its spread via commercial cycads.
Indigenous cycads in the genus Cycas in Micronesia would be at risk should the spread of CAS be left unchecked in these regions (Muniappan, 2005; J. Haynes, pers. Comm). CAS has been reported in the Taitung Cycad Nature Reserve, Taiwan, home of the endemic prince sago (see Cycas taitungensis in IUCN Red List of Threatened Species). A recent survey conducted in the reserve by the Taiwan Forestry Research Institute found that 90% of prince sago were infected by CAS, mortality was, however, found to be less than 3%.
The scale of the female hibiscus snow scale (Pinnaspis strachani (Cooley)) resembles A. yasumatsui, but P. strachani is far less common on cycads in southern Florida (Howard et al. 1999).
In the field, female A. yasumatsui resemble the magnolia white scale (Pseudaulacaspis cockerelli (Comstock)), which is also common on cycads in Florida. The two can be distinguished under a 10X hand lens, with the scale removed, using three features: 1) the colour of the body of all stages and of the eggs of A. yasumatsui is orange, except recently molted individuals, which are yellow. The eggs and all stages of P. cockerelli are yellow. 2) A. yasumatsui has an expanded prosoma. 3) Scales of A. yasumatsui are usually more numerous on the lower surface of leaves, while those of P. cockerelli are more numerous on the upper surface (Howard et al. 1999).
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
Integrated management: Research has indicated that maintaining Aulacaspis yasumatsui (cycad aulacaspis scale (CAS)) populations at a rate that does not threaten the health of plants requires multiple control measures (Wiese and Mannion, undated). The long-term solution may lie in biological control, however, in the short term it is necessary to control the pest on as many plants as possible by treating plants and preventing further spread (IFAS, 2005).
The Cycad Aulacaspis Scale Pest Alert notification released by the IUCN SSC Cycad Specialist Group gives details on description, mode of attack, range, vulnerable species, images and control options.
Compiled by IUCN SSC Invasive Species Specialist Group (ISSG)
Cultural practices have the potential to prevent the spread of the cycad aulacaspis scale (CAS), and keep populations at low levels. Pruning infested plants is an example of this. The crawler stage can be spread via pruning equipment, or by infested clippings which are not discarded properly. Hence, it is good practice to clean pruning equipment before moving to another plant, and to destroy infested clippings (Hodges et al. 2003). Growers can also isolate infested plants or groups of plants from non-infested plant material. As crawlers can be blown by the wind over considerable distances, the direction of the wind should be taken into consideration when isolation is needed (Hodges et al. 2003).
However, Dr F. W. Howard (pers. comm., 2005) observes that "CAS is so virulent that measures like pruning or altering the air flow have no significant effect on the spread of this scale. In areas where this scale insect is prevalent in Florida, shortly after pruning the infested fronds from a cycad, the cycad becomes re-infested, either from neighbouring cycads, from crawlers carried on air currents, or from roots of the same plant. And repeated pruning is detrimental to the cycad plant".
It could also be helpful in the long term to use ornamental cycads which are resistant or not preferred by the cycad scale, but which give a similar effect to the more susceptible Cycas revoluta. Dioon spinulosoum is a good example. By relocating plants to where they have more space, and by removing dense shrubs blocking air flow, cycad scale infestations appeared to decrease in intensity in one study (Wiese and Mannion, undated).
The scale covers of the insect remain on the plant long after the insect itself dies, and previous scale sites may continue to look chlorotic even though treatment has been successful (Hodges et al. 2003). It is possible to loosen these old scales by soaking the excised frond in soapy water overnight, but similar solutions sprayed onto the plant had no effect (Howard et al. 1999). Spraying small plants with a hard stream of water from a hose has found to be effective in slowing the scale down, if done regularly and thoroughly (Mannion, pers. comm., in IFAS, 2005). With a severe scale infestation, it may be necessary to remove all the fronds before undertaking a chemical application (IFAS, 2005).
Initially, CAS was managed using pesticides and oils recommended for other armoured scale insects. Horticultural oil (Ultrafine, summer oil, volck oil, dormantoil, etc) or Organocide (95% fish oil) are recommended, and are somewhat effective with minimum disruption to beneficial insects (IFAS, 2005). These work well if used in a weekly regime (Marler, 2004), and are more successful if the infestation is light, and good foliar spray coverage is possible (Emshousen et al. 2004, Weissling et al. 1999). These products are all sold for the control of scales (IFAS, 2005).
Weissling et al. (1999) state that spraying with oil provides the most consistently effective treatment for cycad scale, using fish oil mixed with water at a rate of 1 part oil to 100 parts water. The spray should be directed at the lower surfaces of the fronds, and also the stems. This method works best as a preventative to prevent crawlers settling on the plant, as well as killing some of the mature females. Experiments have shown that a nearly 100% kill of mature females on the roots of cycads is observed following dipping treatments with 2% horticultural oil (Hodges et al. 2003).
Greater scale mortality can be achieved by mixing oils with a contact insecticide such as Malathion or Sevin. However, these can negatively impact any biological control agents which may have been released (Hodges et al. 2003). Frequent oil treatments can result in an unsightly build up of oil and dead scales. These can be removed by occasionally hosing off old oil and scales (Hodges et al. 2003). Contact pesticides, such as Malathion, kill insects by touching them. Malathion can quickly control a heavy infestation, but is a broad-spectrum insecticide and can cause phytotoxicity to new growth on cycads, as well as killing natural predators of the scale (Wiese and Mannion, undated; Emshousen and Mannion, 2004; in Emshousen et al. 2004). Systemic pesticides, such as Acephate, dimethoate, disyston, and imidacloprid, move into the sap system of the plant, and kill the insect when it feeds on the sap (IFAS, 2005). It is suspected that cycads may undergo periods when their metabolic activity decreases so that they do not absorb systemic insecticides, but this is not proven (Weissling et al. 1999).
Dimethoate (Cygon) can result in a high rate of kill on containerised cycads, but has had mixed results in the field (Hodges et al. 2003). However, its production has been discontinued (IFAS, 2005). It can quickly control a heavy infestation, but is also a broad-spectrum insecticide which can cause phytotoxicity to new growth on cycads, as well as killing natural predators (Wiese and Mannion, undated; Emshousen and Mannion, 2004; in Emshousen et al. 2004).
Containerised cycads treated with imidacloprid have been observed to remain virtually free of scale over a period of a year in one study, although the rates involved may be higher than may be practical in the horticultural industry. Results were however inconsistent for field-grown cycads (Howard et al. 1999). In the form of Merit or Marathon, imidacloprid may not be very effective for cycad scale (IFAS, 2005). As the active ingredient in Imicide, imidacloprid can be applied as a trunk injection using a closed microinjection system. This is well suited for forestry use as only a small amount of material, a 2, 3, or 4 mL injectable capsule is used to treat each plant. None of this will be lost to spray drift or carried away by rain water, and it will only impact insects which feed directly or indirectly on treated cycads (Moore, 2005a). This has at least initially proven successful in controlling an infestation of cycad scale in California (Tattar, 2004).
Insect growth regulators, such as Pyriproxyfen (Distance) and dinotefuran (Safari), are another option. Safari is commercially available only, and expensive, although the cost per application is economical. Appropriate pesticide protective equipment is essential as Safari is very water soluble (IFAS, 2005).
Pyriproxifen, available as Distance, has proven to provide excellent control of CAS on lightly infested plants, and adequate control on densely infested plants. It does not cause any plant tissue damage. Pyriproxifen inhibits production of viable eggs by females, sterilises females, and inhibits metamorphosis of immature scale. It is less likely to disrupt any control by parasitoids than some insecticides. As pyriproxifen breaks the life cycle of the scale by preventing development, it takes a full life cycle of the scale before control can be established. Future studies need to examine the period of effective control after a treatment and how pyriproxifen will affect natural enemies (Emshousen et al. 2004). Wiese and Mannion (undated) report that pyriproxifen did not appear to effect the presence of the predatory beetle Cybocephalus binotatus. Marler (2004) states that ‘Distance’ appears to work well for a period of up to six months. It is recommended that any spraying should be undertaken every other week in warmer weather (above 70ºF), and once a month in colder weather (below 70ºF). The spray application needs to be extremely thorough in order to be effective, as any gaps in coverage allow the population to rebound quickly.
Nearby infested plants can also allow re-infection. The soil under the cycad fronds must also be treated at the same time. (IFAS, 2005), as scale insects which survive in the roots of the plants may be the source of the rapid re-infestations which have been seen following chemical control of the above-ground part of the plant (Howard et al.
APHIS (Animal and Plant Health Inspection Service) is proposing to release parasitic wasps of the genus Coccobius and Encarsia and a predaceous beetle, C. binotatus in the continental USA and US territories in the Caribbean, to reduce the severity of cycad scale infestations. APHIS states that there is “no evidence that the release of these biological control agents will adversely affect threatened and endangered species or their habitat” (APHIS, 2002). The predaceous beetle C. binotatus and the parasitic wasp Coccobius fulvus were released in Florida in 1998, by the Tropical Research and Education Centre (TREC). A further release of 15,000 C. fulvus was made by DPI (Division of Plant Industry, Florida Department of Agriculture and Consumer Services) between February and April of 2002 in Brevard, Broward, Dade, Hillsborough, Indian River, Lake, Manatee, Martin, Orange, Palm Beach, Pinellas, Sarasota, and St. Lucie counties. These biological control agents appear to control the scale very well during some periods, but the scale undergoes outbreaks of varying severity. (Hodges et al. 2003).
C. fulvus is native to the region of Thailand where the cycad scale naturally occurs. It parasitises the adult female scale, helping to keep the scale population under control. Research indicates that the wasp population will never be enough to control the scale alone, but will be consistently parasitising a percentage of the scale all the time (Wiese et al. 2005). C. fulvus could be used to assist with controlling CAS in areas where a chemical spray such as pyriproxifen cannot reach (such as tall or dense plants) (Wiese et al. 2005). The predacious lady beetle, Rhyzobius lophanthae has been introduced from Maui to Guam (Moore, 2005a). It has been observed that there is much less scale on plants with the beetles (A. Brooke, pers. comm). A proposal from the University of Guam for further exploration of natural enemies in Southeast Asia may result in the discovery of more effective biocontrol agents (Muniappan, 2005). It should be noted that the use of oils (Organocide or paraffin-based horticultural) is more compatible with biological control than foliar applications of synthetic organic insecticides (Hodges et al. 2003). Preliminary findings indicate that C. binotatus, at least, is not affected by the use of pyriproxifen (Distance) (Wiese and Mannion, undated).
Germain, J.F. & G.S. Hodges. 2007. First report of Aulacaspis yasumatsui (Hemiptera: Diaspididae) in Africa (Ivory Coast), and update on distribution. Florida Entomologist 90:755-756. http://www.fcla.edu/FlaEnt/fe90p755.pdf
Gill, George, pers. comm., Jan 2006 Senior Adviser - Surveillance & Incursion Response, Post-clearance Directorate, Biosecurity New Zealand.
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Marler, T. March 13 2004. Alien insect attacking Guam's native flora. Pacific Daily News, Lifestyle section, p 20.
Moore, A. 2005a. Evaluation of emergency insecticide treatments for conservation of Guam's endemic cycad, Cycas micronesica, during invasion by the Asian cycad scale, Aulacaspis yasumatsui. Draft proposal.
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Tattar, T.A. & A. Farran. 2006. Control of Asian cycad scale on Cycas revoluta and C. taitungensis using Imicide trunk microinjection. P. 97, In: Proceedings of the 17th U.S. Department of Agriculture Interagency Research Forum on Gypsy Moth and Other Invasive Species, General Technical Report NRS-P-10. http://www.nrs.fs.fed.us/pubs/gtr/gtr_nrs-p-10/gtr_nrs-p-10_097.pdf
Tattar, T.A. 2004. Asian cycad scale: new threat to cycads.
Weissling, T.J., Howard, F.W. and Hamon, A. 1999. Featured creatures: Cycad aulacaspis scale, Aulacaspis yasumatsui Takagi.
Wiese, C. and Mannion, C. Undated. Managing cycad aulacaspis scale (Aulacaspis yasumatsui Takagi) at Montgomery Botanical Center, USA.
Wiese, C., Amalin, D., Coe, R. and Mannion, C. 2005. Effects of the parasitic wasp, Coccobius fulvus, on cycad aulacaspis scale, Aulacaspis yasumatsui, at Montgomery Botanical Center, Miami, Florida. Proc. Fla. State Hort. Soc.
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Perez-Gelabert D, 2019. The Invasive Armored Scale Aulacaspis yasumatsui Takagi (Hemiptera: Coccoidea: Diaspididae) in the Dominican Republic. Proceedings of the Entomological Society of Washington. 121 (3), 525-528.
Reviewed by: F. W. Howard, Ph.D. Associate Professor of Entomology, University of Florida, IFAS. Fort Lauderdale Research & Education Center Florida USA Jody Haynes, Secretary & Webmaster, IUCN Cycad Specialist Group, Miami, FL, USA
Principal sources:Howard et al. 1999. Aulacaspis yasumatsui (Hemiptera: Sternorrhyncha: Diaspididae), a scale insect pest of cycads recently introduced into Florida. Weissling et al. 1999. Featured creatures: Cycad Aulacaspis Scale, Aulacaspis yasumatsui Takagi.
Compiled by: IUCN/SSC Invasive Species Specialist Group (ISSG) with support from the Terrestrial and Freshwater Biodiversity Information System (TFBIS) Programme (Copyright statement)