The two groups of Phomopsis oblonga which invade the phloem of stressed elm trees have been investigated for the production in vitro of boring/feeding deterrents for elm bark beetles The secondary metabolites of this fungus are compared with those of closely-related Phomopsis spp associated with ash and sycamore Active compounds isolated from P oblonga include a novel norsesquiterpene γ-lactone, the tiglic esters of two novel 5,6-dihydro-5-hydroxy-2-pyrones, nectriapyrone, 4-hydroxyphenylethanol, 5-methylmellein, 2-furoic, orsellinic and 3-nitropropanoic acids and mellein-5-carboxylic acid; portensterol and thymine, from P oblonga, were inactive (+)-Mellein and furan-2,5-dicarboxylic acid were obtained as minor metabolites of the ash and sycamore Phomopsis strains, which also produced the norsesquiterpene γ-lactone and one of the tiglic esters