Dunkelblum, E., Institute of Plant Protection, Volcani Center, Bet Dagan 50250, Israel
Harel, M., Institute of Plant Protection, Volcani Center, Bet Dagan 50250, Israel
Assael, F., Institute of Plant Protection, Volcani Center, Bet Dagan 50250, Israel
Mori, K., Department of Chemistry, Science University of Tokyo, Kagurazaka 1-3, Shinjuku-ku, Tokyo 162, Japan
Mendel, Z., Institute of Plant Protection, Volcani Center, Bet Dagan 50250, Israel

It has been demonstrated previously that the sex pheromone of the Israeli pine bast scale, Matsucoccus josephi, (2E,5R,6E,8E)-5,7-dimethyl- 2,6,8-decatrien-4-one (1) is also a potent kairomone of the scale insect's predator Elatophilus hebraicus. Surprisingly, the sex pheromones of M. feytaudi (2) and M. matsumurae (3) also attract E. hebraicus. These results have prompted us to prepare a series of analogs of 1 with variations in the two moieties attached to the C=O group (4-9) in order to probe the structure- activity relationship of the pheromonal/kairomonal response of M. josephi and E. hebraicus. The most selective and active pheromone analog is 8, attracting only M. josephi males and the most selective and active kairomone analog is the M. feytaudi pheromone 2, attracting only adults of E. hebraicus. A dose- response field test of these analogs and the chiral and racemic M. josephi pheromone 1 indicates that the specificity is maintained at a broad range between 25 and 400 μg corresponding to 1. Analog 5, which is neither a parapheromone nor a kairomone, and analog 8, which is only a parapheromone, are not inhibitory to M. josephi or to E. hebraicus. Our study indicates that alterations in the diene side chain of 1, common to all three Matsucoccus pheromones, strongly reduce the kairomonal activity while structural changes in the second side chain significantly reduce the pheromonal activity. The discovery of selective analogs of 1 has practical implications and enables specific monitoring of M. josephi or E. hebraicus. Particularly important is the possibility to mass-trap males of M. josephi without reducing the population of E. hebraicus.