The Asian redbay ambrosia beetle (Xyleborus glabratus) is half the length of an eyelash and resembles an armor-plated, flying coffee bean. It bores into the trunks of trees, leaving telltale strips of frass, and begins to cultivate fungal spores that females transport inside their head. The fungus provides food for the beetle but also cuts off the tree’s food and water transport system, killing a healthy tree within months. This disease, called “laurel wilt,” attacks at least eight Laurel family species, including avocado.
Likely arriving in a shipment from abroad, the beetle was first detected in 2002 in a survey trap near a Savannah, Georgia port. This year, the Florida Department of Agriculture and Consumer Services and the University of Florida Institute of Food and Agriculture Sciences announced that laurel wilt had reached a commercial avocado orchard in Florida. Though the crops have not yet suffered, the fungus kills more than 92 percent of related host species in infested areas. Replacement of the state’s avocado trees could cost more than $400 million (Evans 2009)—not to mention the costs of pest management, lost jobs and avocado sales, and reduced property values.
Environmental costs are more difficult to quantify. Before the disease reached the Florida avocado orchard, it raced through Georgia, North and South Carolina, Mississippi, and other parts of Florida, devastating native redbay tree populations. It also kills native sassafrass, and has been found in dying pondspice and pondberry trees, which are federal and state endangered species, respectively (U.S. Forest Service 2011). “If this invader had been addressed when it first started killing trees near Savannah, the Florida avocado industry wouldn’t be at such high risk now,” says Michael Ielmini, National Invasive Species Program Manager for the U.S. Forest Service. No effective fungicidal treatment for laurel wilt in avocado exists, and several insecticides are still under development. The best strategy is to destroy infected trees and prevent the transport of beetle-infested wood. “Too bad we don’t make guacamole out of redbay fruit,” Ielmini says.