Synergistic Effect of Ethanol to α-Pinene in Primary Attraction of the Larger Pine Shoot Beetle, Tomicus piniperda

α-Pinene and ethanol were released in the approximate proportions 1:0.1, 1:0.9 and 1:9 (at 21°C). Ethanol, released in the range of 3–279 mg/day, generally synergized the attraction of T. piniperda to α-pinene (30 mg/day at 21°C), although attraction to the mixtures varied within and between years. The low release rate of ethanol together with α-pinene attracted a significantly higher number of beetles than α-pinene alone in 1995, April of 1996, and in 1997. Lures with the medium release rate of ethanol were the most attractive only in March of 1996. The high dose of ethanol significantly synergized attraction to α-pinene in 1995 and 1997. The variable attraction of T. pinipeda to ethanol and α-pinene at various release rates and proportions may be due to the temperature dependent nature of beetle antennal sensitivity. At ambient temperatures of 10–13°C. T. piniperda was most attracted to the lures with α-pinene and high release rates of ethanol, at 14–17°C it was most attracted to those with medium release rates of ethanol, and at 18°C and higher it was most attraacted to those with low release rates of ethanol.