From 1909 to 1914, Timberlake was employed by the U.S. Department of Agriculture Bureau of Entomology, as "Agent and Expert" conducting research in biological control of pest insects.
From 1914 to 1924 he was Associate Entomologist at the Hawaiian Sugar Planters Experiment Station in Honolulu, where his research dealt primarily with biological control using parasites and predators.
In 1924 he was appointed Associate Entomologist in the Department of Biological Control at the Citrus Experiment Station of the University of California, Riverside, where he served until retirement in 1950.
They are almost all specialist pollinators (oligoleges) of many species of plants, especially in the Sonoran Desert, where Timberlake carried out extensive collecting for decades.
She and the elderly scientist attended Nixon's presidential inauguration at his invitation, and she died a few years later, in 1972.