Management Information
Aulacaspis yasumatsui Takagi
(cycad aulacaspis scale; Asian cycad scale)
Compiled by the Invasive Species Specialist Group (ISSG)
Cultural
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).
Physical
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).
Chemical
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.
1999).
Biological
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).