Abstract: The sex pheromone components of Dendrolimus punctatus consists of （Z，E）-5，7-dodecadienyl，（Z，E）-5，7-dodecadienyl acetate and （Z，E）-5，7-dodecadienyl propionate．To reduce isomerization and oxidation of above conjugated diene compounds，pheromone baits of different formulations and substrates were made and tested for their trapping efficiency in the field．In the 19 day-test，the trapping efficiency of natural rubber baits did not increase even if they were replaced every 5 days．Similar results were obtained with silicon rubber baits．Moreover，other baits such as adding an antioxidant （topanol CA）or a high purified pheromone did not give better trapping efficiency than the natural rubber ones．However，the baits formulated with compounded rubber septa attracted males twice as many as that by the natural rubber bait. After the field test， only 12%～16% of the pheromone components were isomerized in the compounded rubber baits，while 69%～87% isomerization occurred in the natural rubber baits．The residues of pheromone components and their isomers in the compounded rubber baits were four times as much as that in the natural rubber baits．These data suggest that higher trapping efficiency of the pheromone baits formulated by compounded rubber septa was due to the increase in the stability of the pheromone conjugated diene components and the lower but more constant releasing rate of the pheromone in these dispensers．

Key words: Dendrolimus punctatus, pheromone, conjugated diene, isomerization, substrate