University of Redlands

Plant-Insect Interactions: Coast Live Oak

Many insects are associated with the Coast Live Oak (Quercus agrifolia). Some have no known negative impact on the oak, while the presence of others can have dramatic and even fatal effects.

Associated Insects (in brief)

Goldspotted Oak Borer Agrilus auroguttatus (Coleoptera: Buprestidae)

Identification: Adult beetles are about 10mm long and are somewhat bullet shaped1. They can be black or metallic green and often have six gold-colored spots1. Larvae are grub-like with “two pincherlike spines at the top of the abdomen”1.

Figure 1 Different life stages of the Gold Spotted Oak Borer from UC Statewide IPM Program, 2013

Native Range: Originally from southeastern Arizona. Detected in Riverside in 20042

Ecological Notes: Larvae extensively feed on the inside of oaks, resulting in disrupted water and nutrient uptake which can result in the death of the tree1. Adults feed on leaves, but their impact is negligible1.

Control Measures: Remove and destroy infested trees. Treat remaining stumps with insecticide1. Two parasitoid wasp species (Stanycolus simplex and Calosota elongata) as well as a predatory mite (Pyemotes tritici) can be used as a biological control1.


California Oak Worm and Moth Phryganidia californica (Lepidoptera: Notodontidae)

Identification: The worm is black with long yellow stripes while moths are about 15mm long and tan in coloration3.

Figure 2 California Oak Worm from UC Statewide IPM Program, 2009 

Figure 3 California Oak Moth from USDA 2006


Native Range: Coastal California and parts of the Inland Empire3.

Ecological Notes: Caterpillars are voracious eaters and can completely defoliate trees – this rarely, if ever, kills the tree3.

Control Measures: Since the California Oak Worm and Moth are native to California, their presence usually does not warrant chemical control measures4. Instead, natural predators such as parasitic wasps and parasitic flies can be utilized to control their population4


Oak Twig Girdler Agrilus angelicus(Coleoptera: Buprestidae)

Identification: Adult beetles are metallic brown or bronze and are about 7mm long3. Larvae are white, legless, and can be up to 19mm long3.

Figure 4Adult oak twig girdler from BugGuide copyright: Peter Bryant 20095


Native Range: California, Oregon, and Nebraska3.

Ecological Notes: Larvae bore into twigs and create flattened, spiral tunnels which kills the twigs and can cause parts of the oak canopy to die3

Control Measures: This beetle appears to target oaks weakened by drought and does not kill the oak3. Its presence does not appear to necessitate management3.

Further Information and References:Hundreds of species interact with the Coast Live Oak; as such, this document falls short of describing the nuance and plethora of insect interactions with this particular tree.

If you would like to learn more, refer to the following websites and publications:

  1. UC Statewide IPM Program. 2013. “Goldspotted Oak Borer: Integrated Pest Management for Land Managers and Landscape Professionals.” Compiled by M. L Flint, M. I. Jones, T. W. Coleman, S. J. Seybold. Edited by M. L. Flint and M. L. Fayard.
  2. Tom W. Coleman and Steven J. Seybold. “Goldspotted Oak Borer in California: Invasion History, Biology, Impact, Management, and Implications for Mediterranean Forests Worldwide.” in Insects and Diseases of Mediterranean Forest Systems,ed. Timothy D. Paine and François Lieutier (Springer International Publishing Switzerland, 2016), 663-697.
  3. US Department of Agriculture: Forest Service. 2006. “A Field Guide to Insects and Disease of Californian Oaks.” Compiled by Tedmund J. Swiekcki and Elizabeth A. Bernhardt.
  4. UC Statewide IPM Program. 2009. “California Oakworm: Integrated Pest Management for Home Gardeners and Landscape Professionals.” Compiled by S. Swain, UC Cooperative Extension, Marin Co.; S. A. Tjosvold, UC Cooperative Extension, Santa Cruz Co.; and S. H. Dreistadt, UC Statewide IPM Program. Edited by M. L. Flint, P. N. Galin and M. L. Fayard.
  5. Image from Peter Bryant. 2009. “Beetle – Agrilus angelicus,”
  6. US Department of Agriculture: Agricultural Research Service. 1982. “An Illustrated Guide to Plant Abnormalities Caused by Eriophyid Mites in North America.” Agriculture Handbook no. 573. Compiled by Harford H. Keifer, Edward W. Baker, Tokuwo Kono, Mercedes Delfinado, and William E. Style.

Biographer: Hannah Bockenfeld '18 BIOL 260: Entomology, Spring 2018