Freilandtest zur Attraktivität von Monoterpenen und Ethanol für den Borkenkäfer Tomicus piniperda L (Col., Scolytidae)

Abstract: Field investigations into the attraction of Tomicus piniperda L. (Col., Scolytidae) to monoterpens and ethanol . In northern German pine forests, ethanol and various monoterpenes have been tested in flight‐barrier slot traps and in combination with both trap trees felled 4 weeks before baiting and standing pines debarked at the same time near the ground by forming a 20‐cm‐wide barkless girdle around the stem. The host volatiles ethanol (et), (‐)‐α‐Pinene (ap), (‐)‐β‐Pinene (bp), terpinolene (tp) and the pheromones myrtenol (my) and transverbenol (tv), separately tested in traps, totally failed to lure Tomicus piniperda during the main flight period from 17th to 28th April, 1994. In combination however, these volatiles, except bp + et and tv + et, have been successful in slot traps, but at a very low level compared to some combinations at trap trees in the same pine stand. In traps, the combination my + bp + tp + et caught most (5 + 13 specimen in two replicates), but the differences with respect to my + tv + bp (9 + 4), to bp + tp + et (3 + 8), or to ap + et (2 + 8) are not significant (χ 2 test for equality of frequencies in k classes). Additional monoterpene‐combinations on trap trees did not enhance the number of boring (entrance) holes: trap trees without any additional volatiles (untreated control) had 308 holes (two replicates: 83 + 225), trap trees with additional host volatiles (bp + tp + et) showed 285 (134 + 151) holes, but trap trees with pheromones combined with β‐Pinene (my + tv + bp) showed 25 (19 + 6) entrance holes only. This strong reduction in attack density points to a repellent effect of these pheromones when applied to trap trees. The standing pines which have been to be weakened by the narrow debarked girdle and treated the same way as the trap trees were not attacked at all. Thus, the main attractive components must come from trees more weakened than can result from this way of debarking, i.e. from felled (or windthrown) trees and, of course, from logs. These findings again reveal that aggregation pheromones do not play a substantial part in the chemical host‐recognition system of T. piniperda compared to the evident strong attraction of uninfested logs. The obvious question concerning the biological meaning of the existing pheromones such as transverbenol and myrtenol should lead to investigations into an eventual short‐distance communication system, e.g. for mate‐finding or — more likely — for spacing. The latter would demand a repellent effect of these pheromones, as observed in the trap‐tree experiment. The use of host volatiles in practical forest protection — if at all — will probably be restricted to trap‐based monitoring systems and biological control: the most economic and promising volatile combination is obviously ap + et, and this is also the case with respect to Swedish findings, according to which ap + et‐baited logs had much less offspring of T. piniperda than unbaited logs had, as a result of the effect of lured predators and competitors.