Article of Interest from a Previous Issue
Questions & Answers about the
By F. W. Howard, Associate Professor of Entomology,
(This article originally appeared in the December 1999 issue of The Cycad Newsletter)
In 1996, unusually high infestations of a small white scale insect were observed on cycads in the southeastern part of Miami, Florida. Initially, it was thought that this was the Magnolia white scale insect, Pseudaulacaspis cockerelli (Cooley) which was already known as a common pest of cycads and many other plants in Florida (Howard 1989). However, scale insect experts identified it as Aulacaspis yasumatsui Takagi, a scale insect that was previously unknown in Florida. Entomologists refer to it by the vernacular name, 'cycad aulacaspis scale insect.'
Dr. Sadao Takagi of the University of Hokkaido, Japan, described Aulacaspis yasumatsui in 1977 from specimens collected from cycads in Thailand. It was probably introduced into Florida on cycads imported from Southeast Asia. It spreads to new cycads rapidly, builds up dense populations, and if not controlled it frequently causes the death of the cycad. Following are answers to frequently asked questions concerning this scale insect.
Q. What does the cycad aulacaspis scale insect look like, and how can it be differentiated from other species of scale insects?
A. The cycad aulacaspis scale is in the armored scale insect family (Diaspididae). They are very tiny insects (about 1 millimeter long). They make a scale out of wax and live beneath it. The scale itself is a little more than a millimeter long. It is white, with a little yellow spot at one end. The spot is actually the shed skin of the first stage larva.
An armored scale insect that is very similar in appearance to the cycad aulacaspis scale insect is the Magnolia white scale insect. Both species produce white scales that are somewhat teardrop-shaped. However, the Magnolia white scale insect has a strong tendency to infest the adaxial (upper) frond surface, while the cycad aulacaspis scale insect infests the abaxial (lower) frond surface. Also, if the scale is lifted so as to observe the mature female scale insect, the color of this insect is yellow in the Magnolia white scale and bright orange in the cycad aulacaspis scale insect. This is best observed under a hand lens or microscope. At least in Florida, the infestations of cycad aulacaspis scale insect become very dense, eventually forming a snow-like crust. In contrast, Magnolia white scale infestations are usually much less severe.
A scientifically accurate identification of an armored scale insect species can be made only by an entomologist who specializes in scale insects. The specimens must be run through a clearing and staining procedure and mounted on microscope slides and examined under high magnification. The identifications are based on the positions and shapes of very minute morphological structures of the insect.
Q. What parts of the plant become infested with the cycad aulacaspis scale insect?
A. The cycad aulacaspis scale insect infests all parts of the cycad - the fronds, cones, stems, and even the roots.
Q. How does the cycad aulacaspis scale insect affect its host plant?
A. Armored scale insects feed by piercing into plant tissue with their very thin stylets and drinking the plant juices. They thus drain energy from the plant, and this is thought to greatly weaken the plant if the scale insect infestation is dense.
There is increasing evidence that in addition to draining energy, the scale insects may inject toxic substances into the plant. As a part of their feeding behavior, they inject saliva into the plant tissues to loosen up the sap so they can imbibe it more efficiently. The plant tissues may react to the saliva of some scale insects, similarly to the way in which our tissues react to mosquito bites. Mosquitoes also inject a little saliva into our tissues. It contains anticoagulants. The little welt that forms is due to a reaction to substances in their saliva.
In infestations of the cycad aulacaspis scale insect there are often hundreds of individual insects per pinna. The fronds and trunk are coated with the insects, so that the plant looks like it was snowed on. Sometimes there are several layers of scale insect. The top layers reach the plant tissue by sticking their stylets through the scales of the layers beneath them! There are also scales on the roots. On large cycads with dense infestations, there are probably hundreds of thousands of scale insects on one plant. Think of having a few hundred thousand mosquitoes biting you for 24 hours a day. That gives you an idea of what a cycad infested with this scale insect goes through!
Q. Which species of plants serve as hosts of the cycad aulacaspis scale insect?
A. The species is known only on cycads, i. e., plants in the order Cycadales. Twenty species of Cycas (Cycadaceae) were exposed to this scale insect in Fairchild Tropical Garden, Miami. All became highly infested. In addition, some species of Dioon, Encephalartos, and Microcycas (Zamiaceae), were infested, as was Stangeria eriopus (Stangeriaceae). Species outside of the genus Cycas usually had lighter infestations than on Cycas and were infested only when in the presence of heavily infested Cycas spp.
Q. What is the present distribution of cycad aulacaspis scale insect?
A. The cycad aulacaspis scale insect is presently distributed in Florida south of Lake Okeechobee. It can be expected to continue its spread northward. Cycads are grown at least as far north as the Carolinas. Although it has been suggested that this scale insect, a native of tropical Asia, may be poorly adapted to survive winters farther north than Lake Okeechobee, we have very little data thus far on its survival at cold temperatures. Soil temperatures are more stable than air temperatures, so the insect's ability to infest roots may enable it to survive relatively cold winters.
After having been found in Florida, the cycad aulacaspis scale insect has been found in the Cayman Islands and St. John (Caribbean Region), Hawaii, and Hong Kong. We have received unconfirmed reports that it has been found in additional localities and are attempting to verify these.
Q. How did this insect get spread to so many places?
A. Armored scale insects are moved from country to country on infested host plants. It is easy for this to happen, because they are tiny, are sessile (stuck to the plant so that they don't fall off or fly off when the plant is moved), are often hidden in crevices or under fiber of their host plants, and the host plant furnishes all of their needs. All it takes for an armored scale insect to become established in a new country is for one female to slip through quarantine inspections. One female can lay 100 or more eggs and quickly get a new generation going. As soon as their host plant arrives in a new country, scale insects are in business.
The propensity for armored scale insects to be introduced into new countries was evident in a survey of the armored scale insect species of Louisiana. Of the 77 species found there, about half were introduced species (Howard & Oliver 1985).
Q. How is the insect spread locally, that is, from cycad to cycad?
A. The only winged form of armored scale insects is the male, and males cannot spread infestations. Their only function is to mate with females. The female not only is wingless, but legless. The only stage which can disperse to new plants is the first larval, or crawler, stage. Crawlers are extremely tiny insects barely visible to the naked eye. They have six legs and walk usually no more than a few centimeters from where they hatch from eggs, which the female has laid in a cluster beneath her scale.
It has been shown in studies of many species of armored scale insects that they spread to new host plants via air currents. They are extremely light and buoyant. This type of dispersal is considered passive dispersal, because they depend on chance to be deposited on a suitable host plant. Undoubtedly, many individuals perish, but if only one female lands on a suitable host the scale insect can become established on it.
Q. Why is this scale insect a worse pest than most other scale insects of cycads and other ornamental plants?
A. The main reason is that it builds up dense infestations very quickly. This is probably due to the fact that it was introduced into Florida without the natural enemies that control it in its native home in Southeast Asia. All the other scale insects commonly found on cycads in Florida are usually under control by parasitic wasps, coccinellid beetles, or both.
Armored scale insects in general are difficult to control with insecticides. Contact insecticides can be effective against the crawler stage, but in the cycad aulacaspis scale insect, crawlers are constantly hatching. The pest has been temporarily controlled with frequent applications of contact insecticides over a period of many months, but this is an inadvisable method. Systemic insecticides are effective against many scale insect pests, but we have experienced inconsistent results with systemic insecticides against this species. Sometimes we get excellent control, sometimes control is very poor. We suspect that this inconsistency may be related to the peculiarities of the metabolism or vascular system of cycads.
Finally, the ability of this species to infest roots makes it an unusually formidable pest. We have several times eliminated these scale insects from the aerial parts of the cycad, only to experience a rapid re-infestation from the roots.
Q. What is the basic life cycle of the cycad aulacaspis scale insect?
A. Eggs incubate in about one to two weeks. After hatching, the crawlers wander usually not more than an hour and not more than a few centimeters and then settle on the plant and begin piercing into the tissues with their stylets. Some crawlers may be carried to other host plants, then wander briefly and settle. This is when the insect begins to build the scale. To do this, it exudes threads of wax, which it then sculpts into an igloo-like structure. The female stays beneath the scale for the rest of its life. The male remains beneath the scale until it is mature, then leaves it to fly and search for a female.
The first instar develops to second instar in about two weeks. About a month after hatching, the second instar molts. In some cases the third instar is a mature female. Males undergo four instars and then emerge as mature males. After mating, the female lives about one more month in which she lays about 100 or more eggs that accumulate beneath the scale. Crawlers leave the scale as they hatch. We recently published a paper that provides more complete details of the life history of this scale insect (Howard et al. 1999).
Q. How can a cycad grower control this scale insect?
A. We have obtained excellent control of cycad aulacaspis scale in containers with foliar applications of cygon, but under the conditions of our experiment (which involved exposure to high density populations of the scale insect) the plants were quickly re-infested.
We sometimes obtained excellent control of this scale insect on field-grown cycads with cygon, but at other times this insecticide was not effective.
Imidacloprid as a soil drench at high rates (up to about 1/5 ounce/5-gallon container) was effective in controlling the scale insects on cycads in 5-gallon containers, but no product containing this compound is labeled at such high rates, and in any case would be uneconomical. We thus far have not obtained effective control of cycad aulacaspis scale insect using imidacloprid at label rates on container-grown or field-grown cycads.
Two different commercial products containing fish oil were consistently effective in controlling this scale. Also, we have reliable reports that ultra-fine horticultural oil was similarly effective in controlling cycad aulacaspis scale on a large number of cycads in Miami. Oils have long been used for control of armored scale insects. The oil covers the insects, blocking their air supply. In addition, oils may be repellent or in some way prevent crawlers from settling on plants. The oil products that we tested were highly effective in preventing crawlers from settling on plants, and in some cases killed a large portion of the female scale insects.
It is difficult to obtain thorough coverage of cycads with oils. The cycad aulacaspis scale insect develops mostly on the abaxial ('lower') frond surfaces, and these surfaces are often hard to reach with sprays.
We don't yet have good data indicating how often cycads must be sprayed with oils to control this pest. Based on observations in several plantings, weekly sprayings for a few months or more eventually resulted in almost complete control of the scale on fronds and stems. However, we are concerned that the accumulation of oil deposits on the plant from so much spraying may possibly be detrimental to the plant.
A method that we have been trying lately involves spraying with water in combination with the application of a fish oil product. One needs a garden hose nozzle that focuses water in a hard spray to spray off as many scales as possible. Many of these are old scales of dead scale insects. The water spray also helps to clean off some of the oil residues from previous sprayings. It is fairly easy to spray old scales off of petioles and stems, because they are relatively rigid. It is more difficult to spray them off of pinnae, because of their flexibility. But by supporting the pinnae with one hand and spraying with the other it is possible to remove a fairly large portion of the scales. Following the spraying with water, we apply the oil product.
Q. Are there any natural enemies that help control the cycad aulacaspis scale insect?
A. In 1997 and 1998, two natural enemies of the cycad aulacaspis scale insect were introduced into southern Florida from Thailand by Dr. Richard Baranowski and his co-workers at the Tropical Research & Education Center in Homestead. The National Biological Control Research Center, Kasetsart University, Thailand, cooperated in this work. These include a predaceous beetle, Cybocephalus binotatus Grouvelle (Coleoptera: Nitidulidae), and a parasitic wasp, Coccobius fulvus (Compere & Annecke) (Encyrtidae). Many of the cycads where these natural enemies were released became almost free of scale insects.
Q. How can a grower in southern Florida obtain natural enemies for control of the cycad aulacaspis scale insect?
A. The natural enemies are spreading on their own. Although they were released in southern Miami-Dade County, we have found both the beetle and the parasitoid in Davie, Florida. On July 15, 1999, we took five cycads in 5-gallon containers from Davie to the location with the 18 cycads that we were treating with the oil applications referred to above. Since April we had examined hundreds of pinnae from the field-grown cycads and had not observed evidence that they were parasitized. The containerized cycads were infested with cycad aulacaspis scale, some of which were parasitized as shown by the presence of parasitoid exit holes in a small portion of them. Additionally, we observed parasitic larvae inside several mature female scale insects. We did not rear out and identify the parasitic insects, but presumably they were C. fulvus, since no other species is known to parasitize A. yasumatsui in Florida. By August 13, a small portion of the cycad aulacaspis scale insects on field-grown cycads at this locality were parasitized. The cycads were treated with fish oil three times at 10-20 day intervals between August 13-October 4. The last two oil applications were combined with the water spray treatment. We employed a somewhat 'patchy' spraying of older cycad fronds, leaving some scale insects for establishment of the parasitoids.
In pinnae samples collected on September 29, 14.4 percent of 939 mature female cycad aulacaspis scale insects selected at random were parasitized. Only 14.8 percent of the mature female scale insects were alive. Thus, control with the oil product was compatible with the establishment of a biological control agent.
Q. How can cycad growers help prevent further spread of this scale insect to new areas?
A. Armored scale insects are spread to new areas on their host plants. Therefore, if cycads must be moved to new areas, thorough inspection of them for armored scale insects will help prevent their spread. If an incipient infestation is seen in a new locality, destruction of the plant may prevent further spread.
This paper reports results of observations and research. Mention of
any proprietary product does not imply a recommendation or endorsement
of its use by the University of Florida.
Howard, F. W. 1989. Insecticidal control of magnolia white scale and long-tailed mealybug on sago palms. Proceedings of the Florida State Horticultural Society 102: 293-95.
Howard, F. W., A. Hamon, M. McLaughlin & T. Weissling. 1999. Aulacaspis yasumatsui (Hemiptera: Sternorrhyncha: Diaspididae), a scale insect pest of cycads recently introduced into Florida. Florida Entomological Society 82: 14-27.
Howard, F. W. & A. D. Oliver. 1985. Armored Scale Insects (Homoptera:
Diaspididae) of Louisiana. Louisiana Agricultural Experiment Station,
Baton Rouge, Louisiana.
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This page was updated on Tuesday, 10 June 2008.