Experimental evidence supports a hypothesis that oxygen deficiency may be a causal factor in the formation of chemical attractants for the ambrosia beetle Trypodendron lineatum (Olivier). Detectable attractancy can be induced by anaerobic conditions at 20 °C, imposed for 4 hours on fresh sapwood. Maximum attractancy develops within 24 hours of anaerobic processing. The hypothesis proposes that in a log or dying tree stagnation of the translocative and pneumatic systems leads to deficiency of oxygen at the active metabolic centers. The consequent change from oxidative to fermentative metabolism thus induces attractant formation.