NATURAL ENEMIES OF THE RANGELAND WEED WHITEBRUSH (ALOYSIA-GRATISSIMA,VERBENACEAE) IN SOUTH-AMERICA - POTENTIAL FOR BIOLOGICAL-CONTROL IN THE UNITED-STATES

Whitebrush, AEoysia gratissima (Gill. and Hook.) Troncoso (Verbenaceae ), is a weed of rangelands in the southwestern United States. The genu s Aloysia probably originated in southern South America, with the cent er of evolution in Argentina; A. gratissima is also native there. We t raveled 81,550 km in Argentina, Paraguay, and Brazil over a 6-year per iod searching for natural enemies that could be introduced into North America for biological control of A. gratissima and other weeds of ran gelands. We found 82 species of insects and four plant pathogens on va rious species of Aloysia, in addition to the 36 species of insects pre viously reported from the plant genus. Promising candidates for furthe r research for introduction included a new species of rust fungus, Pro spodium tumefaciens Lindquist that produces stem galls, a probable new species of buprestid stem-boring beetle in the tribe Agrilini, a larg e crown-boring cerambycid beetle probably in the genus Calocosmus, a s cale in the genus Cerococcus, an oecophorid moth Timocratica sp. that feeds on bark, and a twig-girdling cerambycid near the genus Arenicia. Only the rust fungus was abundant enough in South America to cause mu ch damage, but the other species might cause greater damage in North A merica if their own parasites were eliminated before release.