Evaluation of (Z)-5-Decen-1-ol as an Attractant for Male Larch Casebearer Moths, Coleophora laricella

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Abstract
Electroantennogram studies on C. laricella males demonstrated that the title compound, (Z)-5-decen-l-ol (Z5-10:OH), elicited the highest response among a series of straight-chain, C10 to C16 alcohols, acetates and aldehydes tested. From selective adaptation of antennal responses it was concluded that an additional type of receptor cell responded to the corresponding acetate, Z5-10: Ac. Field attraction experiments were carried out by using delta-type sticky traps and rubber-cap odour dispensers. The main test sites were located in the Swiss Alps, Black Forest and northwestern Germany, and included both European and Japanese larch stands, having different degrees of C. laricella infestations. At all test sites pure Z5-10:OH proved to be highly attractive to native male moths over a range of different lure doses, with a progressive increase of captures towards the higher (100 μg, 1000 μg) attractant sources. However, following captures of 200-400 moths/trap the “retaining capacity” of the sticky surfaces of the traps were found to decline markedly; in tests of the higher attractant doses at sites of higher moth densities, this “saturation effect” frequently occurred within a few hrs of trap exposure, thus demonstrating the limitation in the use of sticky traps for monitoring economically-relevant C. laricella populations. Trap placement studies (using the standard attractant of 100 μg Z5-10:OH) showed substantial captures only for those traps placed on green branches within the host crowns. The acetate analogue (Z5-10:Ac) strongly reduced male responses to the attractant alcohol (Z5-10:OH) when evaporated from the same trap, admixtures of 0.3% and 1% of this acetate reducing captures by 90% and almost 100% respectively. Possible functions of this inhibitor are briefly considered. No evidence for attractant synergism was obtained during the present study. The results suggest that Z 5-10: OH is a major constituent of the yet unidentified C. laricella sex pheromone.

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