When the cottony-cushion scale, native to Australia, invaded the United States a century ago and threatened the nation's fledging citrus industry, the U.S. Department of Agriculture counter-attacked by importing the scale's natural enemy, the vedalia beetle, from Australia. That first shipment of beetles in 1888 triggered one of the nation's first notable biological control success stories.

Today University of California, Davis entomologist Penny Gullan, a native of Australia, and noted British entomologist Douglas Williams are collaborating on insect scale taxonomy to help prevent a similar exotic pest invasion.

It's all about pest identification, the key to protecting global agricultural crops, including California's $32-billion-a-year agricultural industry.

And trying to ensure there's no identity crisis.

"Taxonomic research provides the framework for the accurate identification of pests and potential pests," said Gullan, a professor of entomology specializing in systematics (taxonomy and phylogeny) and biology of scale insects. Taxonomy deals with the practice and science of classification, while phylogeny involves the evolutionary development and history of organisms.

"Many scale insects are major agricultural pests and it's important to identify them and find their localities, and then their natural enemies-- in case a species is accidentally introduced to other countries," said Williams, during his two-week research trip to the UC Davis campus in late June. No stranger to UC Davis, he first visited the campus in 1966, conferring with UC entomologist Howard McKenzie (1910-68).

The 83-year-old British entomologist, a renowned expert on scale insect taxonomy, retired in 1988 after three decades at the Commonwealth Institute of Entomology (CABI), based in the Department of Entomology, The Natural History Museum, London. He continues his work as a research associate of that museum.

"Dr. Williams and I currently are working on the Neotropical genus Protortonia, which includes Protortonia navesi, a minor pest of cassava in Brazil," Gullan said, "but this insect could become a major pest if introduced to other cassava-growing areas, such as in Africa where cassava is a staple carbohydrate source."

Cassava is grown for its potato-like roots, which are also processed for tapioca flour and starch.

"Many scale insects become pests if they are transported accidentally and become established outside of their native range," Gullan said. "Scale insects are rarely pests in their native range. It is important to be able to identify these potentially invasive exotic species for two reasons. We need to recognize them during quarantine inspections and thus exclude them from entry or spread in the United States if the species is not present in this country. And, if they have established already, identification provides access to published biological data, such as the host-plant range and geographic distribution. This is useful to biological control programs by facilitating the search for natural enemies in the pest's native range."

Gullan said a number of new potential pest scale insects, including other species of the cottony-cushion scale group, could be introduced to the United States. Over the last 20 years, scientists have detected some 21 new exotic species of scale insects in the United States. Eleven are considered pests, and several have pest potential.

At least 255 species of invasive scale insects are now "home" in the United States. They include the white mango scale; pink hibiscus mealybug; black parlatoria scale, a pest of citrus; and a vine mealybug, a pest of fig and grapes.

Gullan is also collaborating with Williams to produce a taxonomic monograph of scale insects from Australia, but their two immediate projects are the Protortonia from South America and the relatives of cottony-cushion scale from Australia.

Gullan noted that the line of world-renowned scale insect taxonomists is rapidly thinning and the knowledge needs to be preserved for future generations.

Williams is sharing his data, illustrations and specimens, including intricate drawings that he created of scale insects. During his career, he authored 176 scientific publications, including six books, on scale insect taxonomy and identification. He also served as a scale insect taxonomist for two years with the USDA, Washington, D.C.

Gullan first met Williams in Australia in 1978, when she was studying entomology at the Monash University, Victoria. In 1981, he examined her doctoral thesis, "A Systematic Revision of the Australian Gall-forming Coccoid Genus Apiomorpha Rübsaamen (Eriococcidae: Apiomorphinae) with Notes on its Anatomy and Biology."

"Scale insects of the genus >i>Apiomorpha feed on eucalypts, but none are pests," said Gullan, who teaches general entomology, systematic entomology and biodiversity, as well as freshman and graduate seminars at UC Davis. Last winter quarter, she and colleague Peter Cranston, also a UC Davis professor of entomology and a citizen of Australia, taught a Quarter Abroad Program on "South African Biodiversity and Conservation" at Stellenbosch University, South Africa.

Invasive pests drain $123 billion a year from the U.S. economy, according to a 2002 congressional report. They reduce agricultural production, lower farm property values, spread disease, contaminate grain, disrupt water supplies and power outages. The figure also includes the cost of control, health costs and other factors.

For photos of the two entomologists at work, see http://www.ucmrp.ucdavis.edu/news/pennygullan.html