If you grow cycads — and especially if you grow Cycas revoluta, the king sago palm — you need to know about Aulacaspis yasumatsui. This tiny armoured scale insect, barely the size of a pinhead, is the most destructive pest of cycads worldwide. It has killed entire populations of Cycas revoluta in cultivation. It has forced botanical gardens to implement emergency protocols to protect irreplaceable collections. In southern Florida alone, it is estimated that more than eighty per cent of sago palms have been killed since the pest arrived in the mid-1990s.
And it is still spreading. From its native range in Southeast Asia, the cycad aulacaspis scale has reached Florida, Hawaii, the Caribbean, Central America, West Africa, the Mediterranean Basin, and parts of East Asia and Oceania. Wherever cycads are grown and traded, the scale follows — hitchhiking on infested plants that pass through nurseries, garden centres and online sales with no inspection. A single fertilised female hidden under a frond can found a colony that kills a mature cycad within months.
This article is a complete guide to understanding, identifying, treating and preventing Aulacaspis yasumatsui. If your cycad is already infested, skip to the treatment section — time matters. If your cycads are still clean, read the prevention section carefully. It is far easier to keep this pest out than to fight it once it has arrived.
What is Aulacaspis yasumatsui?
Aulacaspis yasumatsui Takagi is an armoured scale insect (Hemiptera: Diaspididae) first described in 1977 from specimens collected on Cycas species in Bangkok, Thailand. Common names include cycad aulacaspis scale (CAS), Asian cycad scale, sago palm scale and cycad scale. In its native range — Thailand, Malaysia, Singapore, southern China and parts of India — its populations are kept in check by natural parasitoids and predators. Outside that range, in the absence of these biological controls, the insect reproduces explosively and can overwhelm a cycad in weeks.
Unlike many scale insects that attack a broad range of hosts, A. yasumatsui is restricted to cycads. It does not attack palms, agaves, yuccas or any other plant group. Its confirmed hosts include the genera Cycas, Dioon, Encephalartos, Macrozamia, Microcycas and Stangeria — essentially every major cycad genus. However, it shows a strong preference for Cycas, and within that genus, Cycas revoluta is by far the most heavily attacked species.
How to identify it
What it looks like
Adult females: the scale cover is white, flat, circular to pear-shaped, approximately 1.2 to 1.6 mm in diameter — roughly the size of a sesame seed. The shape is often irregular, distorted by leaf veins or crowding from adjacent scales. If you lift the cover (use a fingernail or a pin), the insect body underneath is orange, and so are the eggs — a key identification character.
Adult males: the scale cover is elongated with parallel sides, approximately 0.5 to 0.6 mm, white to light yellow, with three faint parallel ridges. Males are winged and capable of short flight, but they are so tiny that they are rarely noticed.
Crawlers (first instars): tiny, orange, mobile — the only life stage with legs. Crawlers are the dispersal stage: they walk to new locations on the plant or are carried by wind to neighbouring plants. Once they settle and begin feeding, they lose their legs and become sessile.
Where to look
In light infestations, the scales are found on the underside of the fronds — check the lower surface of leaflets carefully with a hand lens. As the population grows, scales spread to the upper surface, the rachis (leaf stalk), the trunk, the crown, the cones and — critically — the roots, sometimes to a depth of sixty centimetres or more. Root infestation is one of the reasons this pest is so difficult to eradicate: even if you clean the aboveground parts completely, a colony hiding in the root zone can reinfest the plant within weeks.
How to distinguish it from other white scales
Two other white scale insects are commonly found on cycads and can be confused with A. yasumatsui:
Pseudaulacaspis cockerelli (magnolia white scale) — also white, similar size, but it settles predominantly on the upper surface of the fronds (CAS prefers the underside). Under the cover, the insect body and eggs are yellow, not orange. This is the critical difference: orange body = A. yasumatsui; yellow body = P. cockerelli.
Pinnaspis strachani (snow scale) — the female cover is similar to CAS but this species is far less common on cycads in most regions.
The finger test
A quick field test: rub your finger firmly across the white scale crust on an infested frond. If your finger comes away orange or orange-brown, live A. yasumatsui are present. If only white or yellow residue comes off, the scales may be dead (after treatment) or belong to another species. This test is not definitive, but it is the fastest way to check whether living CAS are still active after a treatment cycle.
Biology and life cycle
Understanding the biology is essential for effective treatment — each control measure targets a specific life stage.
Eggs: a mature female lays one hundred or more eggs beneath her protective cover. The eggs are orange. They hatch in eight to twelve days in warm conditions.
Crawlers (first instars): the newly hatched nymphs are mobile, orange, and extremely small. They walk across the plant surface or are dispersed by wind to neighbouring plants. Within hours to days, they settle, pierce the plant epidermis with their stylet, and begin feeding on sap. Once settled, they secrete the waxy cover that will protect them for the rest of their lives.
Second and third instars: immobile, feeding, growing beneath the cover. Development from crawler to mature adult takes approximately twenty-eight days in warm weather. Males develop wings; females remain wingless and legless.
Adults: males emerge briefly to mate (they live only one to two days), then die. Females continue feeding and laying eggs for several weeks. The generation time — egg to reproducing adult — is approximately five to six weeks at summer temperatures. In warm climates, reproduction is continuous year-round with no diapause. This means populations can build from a few individuals to thousands per frond in a matter of months.
Root colonisation: a distinctive and devastating behaviour. Crawlers descend the trunk and colonise the root system, sometimes to sixty centimetres deep in the soil. Root-feeding scales weaken the plant systematically and are invisible to surface inspection. They also serve as a reservoir: if the aboveground population is eliminated by treatment but the roots are not addressed, recolonisation is rapid.
Which cycads are attacked?
All cycad genera are potential hosts, but vulnerability varies dramatically:
Highly vulnerable — Cycas: the preferred host. Cycas revoluta is the most heavily and frequently attacked species worldwide, probably because it is the most widely cultivated cycad and the most commonly traded. Cycas rumphii, Cycas circinalis, Cycas taitungensis and Cycas micronesica are also severely affected. An untreated infestation on C. revoluta can kill the plant within a year.
Moderately vulnerable — Encephalartos, Macrozamia, Stangeria, Microcycas: infestations occur but are generally less explosive than on Cycas. Encephalartos species in botanical collections have been attacked, including rare and critically endangered taxa — a conservation emergency. Microcycas calocoma, one of the rarest cycads on Earth, was infested at the National Botanical Research Institute in Lucknow, India, in 2007 — the infestation was contained and eradicated by intensive treatment.
Less vulnerable — Dioon, Zamia: these genera appear to be significantly less attractive to the scale. Dioon edule in particular is rarely attacked — some authors have suggested it as a substitute for Cycas revoluta in heavily infested areas. Zamia species can be infested but infestations are typically mild and rarely threaten the plant’s life.
Global spread
The history of A. yasumatsui is a textbook case of invasive pest dispersal through the horticultural trade.
Native range: tropical and subtropical Southeast Asia — Thailand, Malaysia, Singapore, southern China, parts of India.
1996: first detected in Miami, Florida, on Cycas revoluta grown as ornamentals. The initial infestation area included Fairchild Tropical Botanic Garden and Montgomery Botanical Center — both holding irreplaceable world cycad collections.
Late 1990s–2000s: rapid spread through Florida, then to Georgia, Texas, Alabama, Louisiana, South Carolina, California, Hawaii, Puerto Rico, the Cayman Islands, the US Virgin Islands.
2000s–2010s: detected in Hong Kong, Taiwan (infesting the endemic Cycas taitungensis in the Taitung Cycad Nature Reserve — ninety per cent of plants infected), Guam (threatening native Cycas micronesica), Côte d’Ivoire (first African record, 2007), Croatia (2008), the United Kingdom (killing a Cycas circinalis in a greenhouse).
Mediterranean Basin: present in southern France, Italy, Spain and likely other Mediterranean countries — arriving on imported Cycas revoluta from infested nurseries. The Mediterranean climate, with warm summers and mild winters, allows year-round reproduction.
The pattern is consistent: every new detection traces back to the movement of infested plants through the nursery trade. The scale cannot fly long distances — it depends on humans to transport it.
Treatment: the five-step protocol
If your cycad is infested, act immediately. Delay is the enemy — populations double every few weeks. The following protocol combines physical removal, contact killing and systemic protection. It requires persistence: a single treatment will not eradicate the pest. Plan for a minimum of four to six weeks of active treatment, followed by monthly monitoring for at least a year.
Step 1: physical removal — high-pressure water
Begin by blasting the plant with a strong jet of water — a garden hose with a nozzle set to a focused stream, or a pressure washer on a low setting. The goal is to dislodge as many live and dead scales as possible from the fronds, rachis and trunk. Work systematically: upper and lower surfaces of every frond, the crown, the trunk from top to base. This step alone removes a large proportion of the population and exposes the survivors to subsequent chemical treatment.
Step 2: remove heavily infested fronds
If fronds are so heavily encrusted that they are brown, desiccated and coated in a thick white crust, cut them off at the base. These fronds are already dead or dying and are serving primarily as breeding substrate for the scale. Bag the removed fronds in sealed plastic bags and dispose of them with household waste — never in garden compost or green waste bins. The scales on the cut fronds are still capable of producing crawlers.
Critical: remove only dead or severely infested fronds. Keep every green frond that still has functional photosynthetic tissue — the plant needs every remaining leaf to produce energy for recovery. A cycad stripped of all its fronds will struggle to survive even if the pest is eliminated.
Step 3: horticultural oil spray — weekly for four weeks
Apply a horticultural oil (summer-weight / ultrafine mineral oil, or a neem oil product) to the entire plant — every frond (upper and lower surfaces), the rachis, the crown, the trunk. Spray until runoff. Horticultural oil works by physical suffocation — it coats and smothers the scale insects — so thorough coverage is essential.
Repeat weekly for a minimum of four consecutive weeks. Each application kills the scales it contacts, but eggs protected beneath female covers continue hatching — successive treatments catch each new generation of crawlers before they can mature and reproduce.
After the initial four-week treatment, continue monthly applications for at least six months to prevent reinfestation from surviving root colonies or wind-blown crawlers from nearby infested plants.
Product examples: SunSpray Ultra-Fine oil, Organocide (USA); neem oil products (international); white mineral oil / paraffin oil (Europe, Australia). Always use a product labelled for use on ornamental plants and follow the dilution rate. Adding a surfactant (spreader-sticker) improves coverage on the waxy cycad fronds.
Step 4: treat the roots
This is the step most gardeners miss — and the reason many treatments fail. The root zone harbours a hidden population of scales that surface treatments cannot reach.
For potted cycads: unpot the plant, wash the roots with a strong water jet to dislodge scale colonies, soak the root ball in a dilute horticultural oil solution (two per cent) for fifteen to twenty minutes, then repot in fresh substrate. Discard the old substrate — it may contain crawlers.
For cycads in the ground: apply a systemic insecticide as a soil drench. In Europe and many other jurisdictions, the options are increasingly restricted due to neonicotinoid regulations. Where available, imidacloprid (a neonicotinoid) applied as a soil drench is the most effective systemic treatment — it is absorbed by the roots and translocated to the foliage, killing scales that feed on the sap. Where neonicotinoids are banned or restricted (the EU, the UK), consult your local plant protection authority for approved alternatives. Acephate (Orthene) is another systemic option in the US.
If no systemic is available: drench the root zone with a dilute horticultural oil solution (two per cent), applied generously to soak the upper twenty to thirty centimetres of soil. This is less effective than a true systemic but better than ignoring the root population entirely.
Step 5: monitor monthly — indefinitely
After the initial treatment cycle, inspect your cycad monthly. Check the underside of fronds with a hand lens. Perform the finger test on any white residue. A single surviving female can restart the cycle within weeks. If live scales reappear, restart the oil spray protocol immediately — do not wait for the population to build.
Biological control
Two natural enemies of A. yasumatsui have been introduced in Florida and some other affected regions:
Cybocephalus nipponicus — a tiny predatory beetle from Southeast Asia that feeds on the scale insects.
Coccobius fulvus — a parasitoid wasp that lays its eggs inside the scale insects.
Both have established in parts of southern Florida and appear to be providing some level of population suppression. However, in most areas, biological control alone is not sufficient to protect individual garden plants — it works at a landscape scale over years, not as a rescue treatment for an infested specimen. Regard biological control as a complement to active treatment, not a replacement.
Prevention: keeping the pest out
Prevention is vastly easier, cheaper and more effective than treatment. Every cycad grower should follow these practices:
Quarantine every new plant. Any cycad acquired from a nursery, garden centre, online seller or fellow collector should be isolated for a minimum of three months before being placed near your existing collection. During quarantine, inspect the fronds (especially the underside), the trunk, the crown and — if possible — the roots. If you see any white scales, treat immediately before introducing the plant.
Inspect regularly. Check your cycads at least monthly — turn over a few fronds and look at the underside with a hand lens. Early detection is the difference between a minor treatment and a life-threatening infestation.
Do not compost infested material. Cut fronds, old substrate and any plant material from an infested cycad should be bagged and disposed of with household waste. Composting allows crawlers to survive and potentially colonise other plants.
Be cautious with second-hand plants. Cycads from garden clearances, house sales and informal exchanges are common vectors. Inspect thoroughly before accepting.
Consider resistant genera. If you are in a heavily infested area and have lost Cycas revoluta repeatedly, consider replacing it with Dioon edule — a beautiful cycad with a similar form that is rarely attacked by CAS. Other Dioon species (Dioon spinulosum, Dioon mejiae) also show low susceptibility.
Can a severely infested cycad be saved?
Yes — in most cases, if the crown (the central growing point) is still alive, the plant can recover. Even a cycad that has lost all its fronds to scale damage will produce a new flush of leaves if the caudex and crown are intact. The recovery is slow — it may take one to two growing seasons for the plant to produce a full new set of fronds — but cycads are extraordinarily resilient plants with enormous energy reserves in their caudex.
Signs that the plant is still alive: the crown is firm when pressed gently, the caudex is hard (not soft or spongy), and new leaf buds are visible at the apex even if all mature fronds are dead.
Signs that the plant is dead: the crown is soft, rotten or hollow. The caudex is spongy, discoloured or foul-smelling when pressed. If the crown is destroyed, the plant cannot recover — there is no dormant bud to activate.
During recovery, provide optimal growing conditions: full sun, excellent drainage, no overwatering, and a single application of balanced slow-release fertiliser in spring. Do not cut healthy green fronds — the plant needs every photosynthetic surface it has.
Bibliography
Howard F.W., Hamon A., McLaughlin M., Weissling T., Yang S.L. (1999). Aulacaspis yasumatsui (Hemiptera: Sternorrhyncha: Diaspididae), a scale insect pest of cycads recently introduced into Florida. Florida Entomologist, 82(1): 14–27.
Takagi S. (1977). A new species of Aulacaspis associated with a cycad in Thailand (Homoptera: Coccoidea). Insecta Matsumurana, new series, 11: 63–72.
Germain J.F., Hodges G.S. (2007). First report of Aulacaspis yasumatsui (Hemiptera: Diaspididae) in Africa (Ivory Coast), and update on distribution. Florida Entomologist, 90(4): 755–756.
Giorgi J.A., Vandenberg N.J. (2012). Review of the lady beetle genus Phaenochilus Weise with description of a new species from Thailand that preys on cycad aulacaspis scale. Zootaxa, 3478: 239–255.
Malumphy C., Marquart C. (2012). Queen sago palm (Cycas circinalis) killed by Asian cycad scale Aulacaspis yasumatsui in Britain. Entomologist’s Monthly Magazine, 148: 147–154.
Muniappan R., Viraktamath C.A. (2006). The Asian cycad scale Aulacaspis yasumatsui, a threat to native cycads in India. Current Science, 91(7): 868–870.