EFFECTS OF VERBENONE ON THE SPRUCE-BARK B EETLE IPS-TYPOGRAPHUS L (COL, SCOLYTIDAE)

Release of antiaggregation pheromone, verbenone, at 93 mg/tree/day fro m 24 polyethylene dispensers (each 50 cm long, filled with 10 ml verbe none) per living spruce (Picea abies) did not prevent attacks by spruc e bark beetle (Ips typographus) despite aggregation pheromone dispense rs (Pheroprax (R)) have been placed much below security distance only 6 m apart of the verbenone-treated spruce in order to trigger a lot of beetles to both the treated and untreated spruces. In opposite, all o f the 6 verbenone-treated spruces were colonized by spruce bark beetle s, 5 of them within 2 days after treatment whereas only 2 of the nearb y neighbouring untreated spruces have been slightly (1 resp. 2 boring holes) attacked 10 days after treatment. On the verbenone-spruces, the boring holes (4-38 per tree) did not much exceed 3 m of height, i. e. the upper border of the verbenone-treated zone beginning 0.5 m above ground. Attacks of spruce bark beetles occured close to and even under the verbenone dispenser. These findings obviously reveal some attract iveness of verbenone in combination with host tree odors. The charge o f verbenone used in this experiment had proved to be well antiaggregat ive in additional trials with rotating slot. traps: traps baited with Pheroprax (R) and verbenone in polyethylene bags caught only 2% of tho se baited exclusively with the spruce bark beetle pheromone Pheroprax (R).But slot traps containing both Pheroprax (R) and verbenone can als o catch much more typographus when positioned among a number of Pherop rax-baited traps close by (40-60% of, of their catches, e. g. within a cross of traps with distances of 2 m between traps). The lack of any repellent activity of verbenone released in large amounts from dispens ers an living trees obviously does not depend on photoisomerization of verbenone, converted to chrysanthenone: After having been exposed eit her to full sunlight or to sunlight within the shelter of a black slot trap, verbenone released from a dispenser within a slot trap baited w ith Pheroprax (R) reduced the response of Ips trpographus at the (in t rap trials) well known level of about 95-98%, regardless of the durati on of the preceding light exposure within the scope of 1 hour to 1 mon th. Presumably, only a small part of verbenone has been converted to c hrysanthenon and the remaining part was still antiaggregative. Merely absolutely unexposed verbenone showed significant higher reduction of spruce bark beetles (98.8%) than the light exposure treatments did. Th is may indicate a very slight loss of bioactivity of verbenone by phot oisomerization.