The aggregation pheromone ofCarpophilus hemipterus(L.), previously isolated and identified using wind-tunnel bioassays, was field tested in California. A 4-d preliminary study in plantings of figs and stone fruits was followed by long-term studies in a date garden (12 mo) and a stone fruit orchard (11 wk). The pheromone was most effective in combination with host-related coattractants such as fermenting whole wheat bread dough or fermenting fig juice. In the date garden, for example, traps baited with pheromone plus bread dough caught an overall mean of 1,152C. hemipterus, but those baited with only the pheromone or dough caught only 23 and 3 per trap, respectively. A semisynthetic volatile mixture of methanol, methyl butyrate, propanal, and apple cider vinegar was nearly as effective as fermenting dough as a coattractant and is a practical, longer-lasting alternative to dough. The pheromone was formulated on rubber septa, which were replaced every 2 wk. There was a 45% decrease in trap catch due to aging of septa from wk 1 to wk 2, but the septa retained activity into the second week despite daily maximum temperatures<40°C. In the date garden, peak response to the traps occurred during June (65% of the total catch), although temperatures were favorable for beetle flight throughout most of the year. In all experiments, both sexes responded similarly. Four other nitidulid species responded significantly to the pheromone ofC. hemipterus:C. mutilatusErichson,C. lugubrisMurray,C. obsoletusErichson, andC. (Urophorus) humeralis(F.). Two other nitidulid species in the study plots,C. freemaniDobson andHaptoncus luteolus(Erichson), responded poorly or not at all to the pheromone.