Abstract
Conifer feeding bark beetles (Coleoptera, Curculionidae, Scolytinae) pose a serious economic threat to forest production. Volatiles released by non-host angiosperm plants (so called non-host volatiles, NHV) have been shown to reduce the risk of attack by many bark beetle species, including the European spruce bark beetle, Ips typographus. However, the most active blend for I. typographus, containing three green leaf volatiles (GLVs) in addition to the key compounds trans-conophthorin (tC) and verbenone, has been considered too expensive for use in large-scale management. To lower the cost and improve the applicability of NHV, we aim to simplify the blend without compromising its anti-attractant potency. Since the key compound tC is expensive in pure form, we also tested a crude version: technical grade trans-conophthorin (T-tC). In another attempt to find a more cost effective substitute for tC, we evaluated a more readily synthesized analog: dehydro-conophthorin (DHC). Our results showed that 1-hexanol alone could replace the three-component GLV blend containing 1-hexanol, (3Z)-hexen-1-ol, and (2E)-hexen-1-ol. Furthermore, the release rate of tC could be reduced from 5 mg/day to 0.5 mg/day in a blend with 1-hexanol and (–)-verbenone without compromising the anti-attractant activity. We further show that T-tC was comparable with tC, whereas DHC was a less effective anti-attractant. DHC also elicited weaker physiological responses in the tC-responding olfactory receptor neuron class, providing a likely mechanistic explanation for its weaker anti-attractive effect. Our results suggest a blend consisting of (–)-verbenone, 1-hexanol and technical trans-conophthorin as a cost-efficient anti-attractant for forest protection against I. typographus.
Highlights
Bark beetles (Coleoptera, Curculionidae, Scolytinae) are a major concern for the forest industry, causing large economic losses during outbreak periods
A total of 2 625 I. typographus were caught in 21 replicates in Trial 1, which was designed to study whether the release rate of tC could be lowered and if 1-hexanol alone could replace a threecomponent green leaf volatiles (GLVs) mixture without compromising the inhibitory effect of the anti-attractant blend
We found no significant difference between the three release rates of tC
Summary
Bark beetles (Coleoptera, Curculionidae, Scolytinae) are a major concern for the forest industry, causing large economic losses during outbreak periods. After infestation by the European spruce bark beetle, Ips typographus (L.) (Fig. 1) [12,13], the most serious bark beetle pest in Europe This compound inhibits attraction to the aggregation pheromone [14,15], which is a mixture of (4S)-cis-verbenol and 2-methyl-3buten-2-ol (Fig. 1) [13]. Its inhibitory effect on I. typographus is strongly synergized by NHV, such as the green leaf volatiles (GLVs) (3Z)-hexen-1-ol, (2E)-hexen-1-ol, 1-hexanol, as well as trans-conophthorin (tC) [20] The latter compound, [(E)-7-methyl1,6-dioxaspiro[4.5]decane] is found in bark of deciduous trees, e.g. birch, (Fig. 1) [20]
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