Abstract 1 Populations of Ips pini (Say) in northern Arizona and western Montana, U.S.A., were studied to determine regional pheromone response and to evaluate seasonal shifts in that response. A range of enantiomeric blends of the attractant ipsdienol, alone and in the presence of the synergist lanierone, were tested during spring and summer seasons over several years. 2 Both populations were most attracted to high levels of (R)-(–)-ipsdienol, and lanierone was highly synergistic. 3 A significant seasonal shift in pheromone response between spring and summer seasons was found in both regions in both years. Shifts resulted in a more specific preference for the pheromone treatment of 97% (R)-(–)-ipsdienol with lanierone. 4 Several coleopteran insect associates of I. pini also displayed responses to the ipsdienol and lanierone treatments. Temnochila chlorodia (Mannerheim) (Trogositidae), Enoclerus sphegeus (F.) (Cleridae) and, to a limited extent, Lasconotus laqueatus (LeConte) (Colydiidae) were attracted to higher proportions of (R)-(–)-ipsdienol with no apparent reaction to the presence of lanierone. Orthotomicus latidens (LeConte) (Curculionidae: Scolytinae) was strongly attracted to (S)-(+)-ipsdienol with Enoclerus lecontei (Wolcott) (Cleridae), Pityogenes carinulatus (LeConte) (Curculionidae: Scolytinae) and Hylurgops porosus (LeConte) (Curculionidae: Scolytinae) demonstrating some preferences for the (S)-(+)-enantiomer. However, lanierone was synergistic for E. lecontei and P. carinulatus, inhibitory for O. latidens, and produced no significant reaction for H. porosus. Elacatis sp. (Salpingidae, previously Othniidae) was attracted to the presence of ipsdienol but displayed no preference to the enantiomeric ratios of ipsdienol or the presence of lanierone.