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Assessing the Role of a Little-known Wood-boring Beetle in Sugarberry Decline

Photo of Female Agrilus macer laying an egg mass on the trunk of a declining sugarberry tree.  Female Agrilus macer laying an egg mass on the trunk of a declining sugarberry tree. Snapshot : Ongoing research seeks to explain an ongoing, severe episode of sugarberry mortality in the southeastern U.S. A rarely collected species of buprestid beetle, Agrilus macer, is attacking dying trees at high densities. USDA Forest Service research results suggest that Agrilus macer is a secondary pest, rather than a primary cause of mortality, and there is no evidence that it is the vector for harmful pathogens.

Principal Investigators(s) :
Horn, ScottOlatinwo, Rabiu
Ulyshen, MichaelFraedrich, Stephen W.
Research Location : North Augusta, South Carolina   
Research Station : Southern Research Station (SRS)
Year : 2019
Highlight ID : 1591

Summary

Large numbers of sugarberry trees are dying in parts of Georgia and South Carolina, but it remains unclear what is causing this problem. USDA Forest Service scientists at the agency's Southern Research Station studied a native but poorly known beetle, Agrilus macer, that is often found attacking dying sugarberry trees in very high numbers. Egg mass densities as high as 13 eggs per square inch were observed on trunks, branches, and exposed roots of dying trees; however, not all dying sugarberry have been attacked by this species, and some trees are capable of overcoming attacks. The egg laying habits of the beetle were found to be extreme among known species of its genus, with females laying groups of 17 eggs on average. The eggs are then covered with a protective cap. Why they do this remains unknown, but it is possible that larvae are better able to overcome host defenses if they attack as a group. Fungi isolated from discolored sapwood around larval galleries did not cause defoliation, dieback, or mortality of sugarberry in inoculation trials. Their findings suggest that Agrilus macer is a secondary pest on sugarberry and does not transmit harmful fungal pathogens, eliminating it as a primary causal agent for sugarberry decline and suggesting further investigation of other pests and pathogens.

Forest Service Partners

External Partners

  • Michelle Cram (USDA FS FHP)
  • University of Georgia

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