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Abstract. Between 1995 and 1999, a monitoring program was implemented in the City of Sacramento, California, U.S., where treatment decisions for elm leaf beetle (Xanthogaleruca luteola) were made based on presence or absence of egg clusters at each generation egg peak. The damage prediction model proposed by Dahlsten et al. (1994) was effective at predicting damage in Sacramento in both the first and second generations. Addition of the Sacramento data collected between 1995 and 1999 to the model does not change the treatment threshold for the first generation but does raise the treatment threshold in the second generation to approximately equal that for the first. A similar model for the third generation suggests a much higher treatment threshold; however, more data are needed for this generation. Subsampling 20% of the susceptible trees and resampling additional trees in areas where egg clusters were found is effective in locating areas of beetle activity. Between 1995 and 1999, an average of 11.3% of trees managed using the monitoring system required treatment. This finding represents a dramatic reduction in pesticide use and cost when compared to the previous strategy of treating all susceptible elms on a calendar basis.
Key Words. Xanthogaleruca luteola; elm; Ulmus, integrated pest management; monitoring; entomology; urban forestry.
The elm leaf beetle (ELB), Xanthogaleruca luteola (Milller), was accidentally introduced into the United States in the 1830s at Baltimore, Maryland, U.S. (Glover 1871; Riley 1883). ELB is now present in North America almost everywhere elms are planted (Davidson 1979). It is the second most important urban tree pest in the western United States and third most important nationally according to a 1986 survey of more than 1,500 urban tree managers (Wu et al. 1991).
The beetles overwinter as adults in sheltered places such as woodpiles, garages, and attics. As the foliage begins to develop in the spring, the adults emerge from their hiding places and feed on the foliage for 1 to 2 weeks before starting to lay eggs. Adult feeding is characterized by small, circular, BB-size holes in the foliage. Eggs are yellow and oblong and are laid in clusters averaging 15 to 20 each. The larvae, which are the most damaging stage, develop through three instars. Larval feeding can be distinguished from adult...