HOST-SPECIFICITY OF 3 POTENTIAL BIOLOGICAL WEED-CONTROL AGENTS ATTACKING FLOWERS AND SEEDS OF LYTHRUM-SALICARIA (PURPLE LOOSESTRIFE)

Lythrum salicaria is a Eurasian herbaceous perennial that has become a serious invader of wetlands in the United States and Canada. Dense mo nospecific stands replace a diverse native flora resulting in the degr adation of these wetland habitats. There are presently no satisfactory means of control. Biological control offers the most promising method of resolving this problem. A root-mining weevil and two leaf-feeding chrysomelids from Europe were released in North America in 1992. The h ost specificity of three additional flower- and seed-feeding species w as investigated. The two weevils, Nanophyes marmoratus and N. brevis, have a wide geographic and ecological range. Both develop exclusively on Lythrum salicaria within its native European range and were found t o be highly host specific during screening tests. Minor adult feeding was observed in no-choice tests on a few other species within the Lyth raceae. Successful larval development was restricted to purple loosest rife. The only known field host of the third species, the gall midge B ayeriola salicariae, is purple loosestrife. Oviposition and successful larval development of B. salicariae in cages and the open field occur red on potted test plants of another three Lythrum species. The introd uction of N. marmoratus and N. brevis into North America is expected t o further reduce seed output and lessen the competitive ability of pur ple loosestrife. Their introduction was approved in 1994. (C) 1995 Aca demic Press, Inc.