Carlos E. Bográn, Boris A. Castro and Scott Ludwig
Assistant Professor & Extension Specialist, Entomology-Plant Pathology & Microbiology, Assistant Professor & Extension Entomologist, and Extension Program Specialist-IPM, respectively; Texas Cooperative Extension; The Texas A&M University System.
Although usually devoid of pests and diseases, sago palms (Cycas spp.) in south Texas have recently become targets of a new scale insect. Severe outbreaks of the cycad aulacaspis scale (CAS) Aulacaspis yasumatsui Takagi (Hemiptera: Diaspididae) have been reported in the Lower Rio Grande Valley where sago palms adorn landscapes and are key crops for commercial nursery growers. This scale is also referred to as the Asian cycad scale. The CAS is an invasive insect pest that poses a serious threat to cycad plants and the valuable cycad industry in Texas. This article provides basic information on identification and biology of this pest along with suggestions for effective pest management.
Like other armored scale insects, Aulacaspis scale insects are protected under a waxy cover comprised of old shed skins of the immature insect. Adult females are different in shape and size than males. The female scale cover is about 1.2 to 1.6 mm in length, flat, circular to pear-shaped, and often distorted due to crowding or due to the veins of the cycad host plant. The female cover is white in color, sometimes translucent. The female scale body, which is visible after removal of scale cover, is broad, wingless, legless, and orange in color. The orange-colored eggs usually are laid underneath the female scale cover. The male covers are elongate in shape, between 0.5 to 0.6 mm in length, light yellow or white in color, with three parallel ridges. The cycad aulacaspis scale is similar in appearance to the less important false oleander scale (Pseudaulacaspis cockerelli) whose adult females have a more slender body.
CAS infestations are much worse than other armored scale insects that affect cycads because it is relatively new in Texas and because it can colonize every part of the plant, including roots. New invasive species are usually free from the natural enemies that keep population under control in its native habitat. Therefore, its populations can increase rapidly in just a few days. Even when scales are controlled in the plant foliage CAS can quickly re-infest plants from root populations. Root infestations are difficult to detect and allow the insect to go unnoticed during shipment.
Fortunately, the CAS has a restricted host range and occurs only on sago palms of the genera Cycas, Dioon, Encephalartos, Microcycas, Stangeria and Macrozamia. There is a preference for sagos of the Cycas genus from which the Queen and King sagos (Cycas circinalis and Cycas revoluta) are highly susceptible to infestations.
CAS causes damage by sucking plant fluids. Initial symptoms of infestation include small yellow spots on the upper surface of fronds. As the infestation progresses, fronds become brown and desiccated. CAS infestations start on the underside of fronds. Heavy infestations contain scales on both upper and lower frond surfaces, rachis, cones, seeds, and main roots as deep as 24 inches (60 cm). Heavy infestations result in multiple layers of live and dead scales forming a waxy white ‘crust’ on the frond surface with insect counts of several thousands per square inch. Uncontrolled infestations can result in plant death in a few weeks or months.
The CAS is native to Thailand and has spread widely mainly through transportation or shipment of infested plants. It currently is distributed throughout many Asian countries, the Caribbean, Southeastern United States, California, and Hawaii. In the continental US it was first reported in Florida in 1996. CAS was first detected in Texas in 2002 but probably did not establish until 2004. Texas counties with known established infestations include Cameron and Hidalgo counties in the Rio Grande Valley from La Joya to South Padre Island, Nueces (Corpus Christi) and Harris County (Katy). The scale was also detected in a retail nursery operation in Brazos County.
The CAS is a tropical and subtropical insect species that reproduces continuously throughout the year. Development time from egg to adult is about 28 days at 77 °F (25 °C) or less at higher temperatures. Females can lay more than 100 eggs in their lifetime. Eggs hatch in 8 to 12 days depending on temperature. Newly emerged first instars (crawlers) disperse to new feeding sites and may be carried a few miles by wind. Once feeding has started, scale insects remain at the same site for the rest of their life cycle. Male scales feed for a short period of time and develop into tiny winged adults.
Integrated Pest Management:
Integrated pest management (IPM) is a strategy to avoid or prevent damage with minimum adverse impact to human health, the environment and to non-target organisms. Successful pest management of scale insects requires a consistent effort and the integration of multiple control tactics. No single control alternative is likely to provide acceptable levels of control against the CAS. Specific pest management recommendations may be different for commercial nurseries and landscapes, for professionals or for homeowners (see specific suggestions below).
Prevent pest problems: Check new plants before purchase or prior to installation to make sure they are free of the CAS. Look for early infestation symptoms and for scales and scale crawlers on the whole plant, especially leaf undersides. Since crawlers are very small, use a 10x magnification lens to facilitate observation.
Detect infestations quickly and monitor pest populations: Visually inspect plants frequently, weekly or every other week, for early infestation symptoms and for the presence of scales. Small populations are always easier to control than large ones.
Act quickly and use effective control tools: The CAS has overlapping generations and populations can increase rapidly. Once infestations are detected, act quickly. Continue to monitor populations to determine if your action or treatment was effective.
Cultural control. Avoid plant crowding to reduce movement of scale crawlers from infested to healthy plants and to facilitate spray treatments, if needed. Remove heavily infested fronds (palm leaves) to reduce population density and enhance control. Pruned plant parts must be disposed of properly to avoid contamination to nearby plants. Place infested material inside a double-sealed plastic bag before discarding. Tools used for pruning must be cleaned before use on non-infested plants to minimize the risk of spreading the pest.
Chemical control. Several insecticides are available and registered to control scale insects.The choice of insecticide is less critical than how the insecticide is applied. Complete plant coverage is essential to control as scales can infest all plant parts. Contact foliar sprays such as horticultural oils and insecticidal soaps require 2 to 3 applications (5 to 10 days apart). Systemic insecticides usually are more effective when applied as soil drenches. Use only products that are registered for ornamental plant use in Texas. See specific suggestions below.
Biological control: Two natural enemies, a predaceous beetle, Cybocephalus binotatus Grouvelle, and a parasitic wasp, Coccobius fulvus (Compere and Annecke) have been introduced into Florida with good preliminary results. In Texas, biological control efforts have begun with a survey of natural enemies for possible mass rearing and distribution in affected localities by USDA/APHIS/PPQ.
Haynes, J. 2005. Aulacaspis Scale: A Global Perspective. The Cycad Newsletter 28(5): 3-6 pp.
Miller, D. and M. Williams. 2004. Aulacaspis yasumatsui, pp 338-339 In Proceedings Southern Plant Diagnostic Network (SPDN) ‘Homoptera’ Workshop. 9-11 December 2004, Gainesville, FL. National Plant Diagnostic Network.
Mannion, C., G. Hodges and A. Hodges. 2006. Regional Pest Alert: Cycad Aulacaspsi Scale, Aulacaspis yasumatsui Takagi. http://www.ncipm.org/alerts/cycadscale/index.cfm USDA-CSREES- IPM Centers, National Plant Diagnostic Network- APHIS.
Weissling, T. J. and F. W. Howard. 1999. Cycad aulacaspis scale Aulacaspis yasumatsui Takagi (Insecta: Hemiptera: Sternorrhyncha: Diaspididae). http://creatures.ifas.ufl.edu/orn/palms/cycad_scale.htm Dept. Entomology, UF/IFAS, Division of Plant Industry, Fla. Dept. Agric. Cons. Serv., Pub. EENY-96.
Womack, M. 2004. Asian Cycad Scale: A New Threat to Sago Palms. Texas Cooperative Extension, Texas A&M University. Nueces County Extension Office. 4 pp.
Note: under certain temperature, humidity, water and shade conditions, pesticides may cause injury to certain plants (phytotoxicity). Generally, apply pesticides during early morning to avoid dew or late afternoon to avoid the hottest part of the day. Water plants 1-2 days before applying a pesticide. Always check the product label for the list of plants that may be injured by the pesticide.