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Goal: Sustain Our Nation’s Forests and Grasslands Assessing the role of a little known wood boring beetle in sugarberry decline

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. (Forest Service photo by Michael Ulyshen)

Introduction

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. Research results suggest that A. 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.

Summary

Large numbers of sugarberry trees are dying in parts of Georgia and South Carolina, but it remains unclear what is causing this problem. SRS scientists 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 A. macer 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 A. 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.

Principal Investigators
Michael Ulyshen, Research Entomologist
Stephen W. Fraedrich, Plant Pathologist
RWU
4552 - Insects, Diseases, and Invasive Plants
Strategic Program Area
Invasive Species
Research Partners
Scott Horn (SRS)
Rabiu Olatinwo (SRS)
Michelle Cram (FHP)
External Partner
Emilee Poole (University of Georgia)