The good bug against a bad weed

Her biological control research on a leaf-eating beetle that targets saltcedar has scored a bullseye.

Hillary Thomas, a doctoral candidate in entomology at the University of California, Davis, has received a $15,000 Robert and Peggy van den Bosch Memorial Scholarship to support her research.

Saltcedar or tamarix (Tamarix spp.), an exotic and invasive pest that threatens waterways, was imported to the United States from the Middle East in the 1880s for erosion control and as an ornamental. As a shrub or small tree, it forms dense thickets, displacing native plants and animals. In the Western United States alone, it impacts several million acres of prime riparian land.

Thomas researches Diorhabda elongata, a saltcedar leaf beetle native to Central Asia that’s a natural enemy of the plant.

She won the award for her project, “Impact of Host-Plant Preferences on Establishment and Efficacy of Diorhabda elongata (Coleoptera: Chrysomelidae), a Biological Control Agent of Saltcedars.” She studies with major professor Frank Zalom, an integrated pest management specialist.

“Hillary is an outstanding young scientist who is committed to the implementation of biological control,” said Zalom. “Her dissertation research on host plant acceptance by the beetles introduced for control of invasive saltcedar is not only useful for that system but will lead to better understanding of the importance of post-release evolution in biological control agent establishment. She is highly motivated, and a joy to work with.”

"The beetle has shown great potential to control the weed in some release areas," said Thomas, who collaborates with the Exotic and Invasive Weeds Unit of the U.S. Department of Agriculture/Agricultural Research Service. "It causes defoliation to the extent that it appears there will be a population-level effect on tamarix stands.”

Thomas’ work initially focused on improving insect establishment success in the Cache Creek watershed, near Rumsey, Yolo County, where Tamarix parviflora grows. Today she compares the host plant preferences of two populations: the field population beetles and its source lab colony.

“It seems there might be an increase in host plant acceptability of Tamarix parviflora by the field population,” Thomas said. “I am repeating both field and laboratory experiments at the moment to determine whether there is substantial evidence to support this.”

The saltcedar's long tap roots enable it to limit its competition by sucking in massive amounts of water. It also drops its salt-infused foliage on the surface, inhibiting other plant growth. It can produce as many as 600,000 seeds annually, according to Joseph DiTomaso of the Department of Plant Sciences. Chemical, mechanical and cultural control techniques are effective, but expensive and temporary.

Three other UC Davis doctoral candidates shared in the Robert and Peggy van den Bosch Memorial Awards.

Amanda Hodson, who studies with major professor Edwin Lewis, of Nematology and Entomology, received $10,000 for her research on “Ecological Influence of Entomopathogenic Nematodes in Pistachio Orchards.”

Andrew Sutherland, a doctoral candidate in entomologist Michael Parrella’s lab, received a $1500 van den Bosch travel award for his “Manual Transmission of Powdery Mildew Fungi Mediated by Activity of an Obligate Mycophagous Beetle (Coleoptera: Coccinellidae).” He will attend an entomology conference in Brazil this year.

The van den Bosh scholarship program provides a total of $60,000 to $80,000 each year for work related to biological control, typically $15,000, $10,000 or $5,000 to the recipients, according to Kent Daane and Nicholas Mills, co-directors of the Center for Biological Control, UC Berkeley. Travel awards total between $15,000 to $20,000, with a maximum of $1,500 given to a student.

The 2008 van den Bosch scholarship awardees also include UC Berkeley students Rebecca Chaplin-Kramer (major professor: Claire Kremen, also a UC Davis Department of Entomology affiliate), Mel Stravrinides (major professor: Nicholas Mills); and Eleanor Blitzer (major professor: Stephen Welter).

Also receiving travel funds were UC Berkeley students Mel Stravrinides and Eleanor Blitzer and UC Riverside students Jason Mottern and Jennifer Henke.

Daane and Mills coordinate the annual scholarship and travel awards programs, created in 1979. A panel of five to seven UC faculty members (from Berkeley, Riverside and Davis with expertise in biological control, ecology or systematics), reviews the scholarship applications. Mills and Daane review the travel award applications.

Robert van den Bosch (1922-1978) served as a researcher, teacher, and an administrator in the Division of Biological Control and the Department of Entomological Sciences, UC Berkeley, from 1963 until his death. A native of Martinez, Calif., he was a lifelong leader and spokesman for the discipline of biological control. His colleagues said he searched tirelessly for natural enemies of agricultural pests, an effort that resulted in the importation and establishment of 17 natural enemy species.

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