Toxicity and Repellency of 4–Allylanisole and Monoterpenes from White Spruce and Tamarack to the Spruce Beetle and Eastern Larch Beetle (Coleoptera: Scolytidae)

Abstract

Monoterpenes found in the oleoresin of white spruce, Picea glauca (Moench) Voss, and tamarack, Larix laricina (DuRoi) K. Koch, and 4-allylanisole (= estragole, methyl chavicol) were bioassayed for their toxicity to adult spruce beetles, Dendroctonus rufipennis (Kirby), and adult eastern larch beetles, D. simplex LeConte. Limonene and 4-allylanisole at 20 ppm were most toxic to spruce beetles at 24 h; whereas, limonene, myrcene, beta phellandrene, and 4-allylanisole were most toxic to eastern larch beetles. Limonene and 4-allylanisole caused 100% mortality to spruce beetle adults exposed to 80 ppm for 24 h. In comparison, limonene, 4-allylanisole, myrcene, and beta phellandrene caused 88-98% mortality to eastern larch beetles exposed to 80 ppm for 24 h. In field tests, limonene, 4-allylanisole, myrcene, and beta phellandrene inhibited the response of the spruce beetle to frontalin; whereas, myrcene and limonene inhibited the response of the eastern larch beetle to seudenol. Limonene, myrcene, and beta phellandrene were found in greater quantities in the wound tissues surrounding the induced reaction zones of white spruce and tamarack than in unwounded tissues which indicates the presence of an induced defensive system. Defoliated tamarack trees responded with increased levels of limonene in the oleoresin during the first 2 yr of successive defoliation, but these levels decreased during the first and 4th yr of successive defoliation. Limonene and 4-allylanisole were the most toxic and inhibitory monoterpenes tested in this study