ASSOCIATION BETWEEN A NATIVE SPITTLEBUG (HOMOPTERA: CERCOPIDAE) ON MONTEREY PINE AND AN INTRODUCED TREE PATHOGEN WHICH CAUSES PITCH CANKER DISEASE

Abstract

AbstractJuvenile Monterey pines, Pinus radiata D. Don (Pinaceae), in a native stand on the Monterey Peninsula, California, exhibited wilted green shoots in the spring of 1996. The pitch canker fungus, Fusarium subglutinans (Wollenweb. & Reinking) P.E. Nelson, Toussoun & Marasas f.sp. pini, was subsequently isolated from 95% of these shoots. Spittle masses produced by Aphrophora canadensis Walley were observed on the symptomless shoots of many of these trees. The pitch canker fungus was isolated from the feeding sites of this insect on 55% of symptomless shoots, and from shoot sections adjacent to these feeding sites on 29% of the shoots. Shoots with spittlebugs feeding on them in May 1996 were more likely to develop pitch canker disease by September 1996 and March 1997 than shoots without spittlebugs. Shoots with spittle masses in March 1997 were as likely to develop pitch canker disease by May and August 1997 as shoots without spittle masses, but the origin of the infection was most likely where A. canadensis feeding had taken place. In a controlled test, the incidence of pitch canker on shoots of potted Monterey pines was dependent on the presence of a spittlebug and a spore suspension of the pathogen. Thus, both field observations and controlled studies show an association between native A. canadensis and the introduced pitch canker pathogen. The role of A. canadensis in the epidemiology of pitch canker disease remains to be determined.