Soapberry Borer, Agrilus prionurus (Coleoptera: Buprestidae): An Exotic Pest Threatens Western Soapberry in Texas

Abstract

Sapindus saponaria var. drummondii (Western Soapberry) is a small- to medium-sized tree native to the western Gulf Region and southwestern US and is valued in urban and rural landscapes. Recently in the United States, it has become host to an invasive insect introduced from Mexico. Agrilus prionurus (Coleoptera: Buprestidae) (Soapberry Borer) was first reported in Travis County, TX, in 2003 and has been detected in 51 additional counties as of December 2013. As its populations expand rapidly in Texas, this invasive pest is killing Soapberry trees >6 cm in diameter. Additionally, it may eventually threaten Western Soapberry populations throughout the tree's range. Infestations of Soapberry Borer are similar to those of A. planipennis (Emerald Ash Borer), a destructive invasive pest of Fraxinus spp. (ash) but not yet found in Texas. Signs of Soapberry Borer infestation include large bark flakes that accumulate at the base of infested trees, galleries between the bark and sapwood, trees that die back from the top, and excessive epicormic sprouts on the lower trunk. Western Soapberry appears to be the Soapberry Borer's sole host in Texas, and trees of this species exhibit little resistance to this introduced pest. Preliminary studies indicate that Soapberry Borer adults emerge and fly from late May to August and that this species has no more than one generation per year in Texas. Preventative and therapeutic treatments with the systemic insecticide emamectin benzoate are showing promise as a means to protect valuable Soapberry trees in rural and urban landscapes.