Long chain alcohols, produced by the fungus Trichoderma citrinoviride as fagodeterrents for aphids control

Aphids are insect pests of great economic impact on agricultural production causing yield losses and reduction of quality products. They damage host plants in different ways, indeed during the feeding phase they subtract sap and spread virus diseases. Chemoreception in aphids plays a fundamental role in host plant selection and in host acceptance, therefore the identification of new compounds that interfere with these processes are of great interest for the development of innovative biotechnical control strategies. In this context, our studies aim to identify fungal metabolites that interfere with aphid feeding behavior and to understand the aphid sensory structures involved in their perception. Our previous studies led to the characterization of three distinct groups of structurally related metabolites, produced by an isolate of the fungus Trichoderma citrinoviride, which exhibit fagodeterrent activity towards different species of aphids. The first two are novel metabolites, characterized as a symmetrical disubstituted hexa-1,3-dienyl ester of acetic acid and a tetrasubstituted cyclohexane-1,3-diol, respectively and named citrantifidiene and citrantifidiol (Evidente et al., 2008). Other two compounds belong to the chemical family of bisorbicillinoids, namely bislongiquinolide and dihydrotrichodimerol (Evidente et al., 2009). Further investigations led to the isolation of a fourth group of compounds. They were identified by spectroscopic, chemical and chromatographic methods as primary alcohols: hexadecanol, octadecanol, cis-9-octadecanol and trans-9-octadecanol. Feeding preferences tests showed that these long chain alcohols have a highly significant fagodeterrent activity towards aphids of the species Rhopalosiphum padi (L.), one of the major pests of cereal crops. Antennal responses, obtained by using a standard electroantennographic technique, showed that these long chain alcohols were not able to stimulate significantly the olfactory sensilla of R. padi. Results of single chemosensory cell recordings carried out with long-chain alcohols indicate that the structures involved in their perception, particularly cis-9-octadecanol and trans-9-octadecanol, are taste cells located on the aphid tarsomeres. The tested alcohols, obtained by T. citrinoviride can modify the aphid feeding activity, thus functioning as signalling molecules that can be potentially utilized for novel applications in biotechnical control of aphid.