Non-host volatile blend optimization for forest protection against the European Spruce Bark Beetle, <i>Ips typographus</i>

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: dehydroconophthorin

(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 transconophthorin

as a cost-efficient anti-attractant for forest protection against I. typographus.