THE STRUCTURE OF THE PHYTOPHAGOUS INSECT FAUNA ON THE INTRODUCED WEEDSOLIDAGO-ALTISSIMA IN SWITZERLAND

Solidago altissima L. was introduced into Europe as an ornamental plan t from North America more than 100 years ago and the phytophagous inse ct fauna of it was recently examined in Switzerland where it has becom e an important weed in disturbed habitats. Rhizomes and aerial parts w ere examined and all insects collected in summer were tested in a no-c hoice feeding test. 18 out of 55 phytophagous insects were found feedi ng on S. altissima in Switzerland and for the remaining 37 the relatio n with the plant was not determined. The insects that have expanded th eir host range to feed on S. altissima since its introduction to Switz erland are almost solely opportunistic, unspecialized ectophages not c losely attuned to the growth cycle of S. altissima. Only 4% of the ins ects were specialists and 9% endophagous. In contrast in North America S. altissima supports 25% specialists and 17% endophages. The native Solidago virgaurea L. in Switzerland supports many more specialists (2 8%) and endophages (23%) than S. altissima here. Possible reasons why almost none of these have switched to S. altissima are discussed. A co mparison is made between the number of insects recruited by S. altissi ma in Switzerland with the number recruited by the exotic plants Herac leum mantegazzianum Som. & Lev. (Apiaceae) in Switzerland and Xanthium occidentale Bertol. (Asteraceae) in Australia. Reasons for different levels of insect recruitment are discussed. The high number of phytoph agous insect species found on S. altissima in North America shows that there should be no shortage of possible control agents and any insect s imported into Switzerland for the biological control of S. altissima would find largely unexploited food sources awaiting them.