We report the first isolation and characterization of insect fatty acid Delta12-desaturase genes, AdD12Des from house cricket (Acheta domesticus) and TcD12Des from the red flour beetle (Tribolium castaneum), responsible for the production of linoleic acid from oleic acid. Sequence analysis shows the cricket and flour beetle Delta12-desaturase genes have evolved independently from all previously known Delta12-desaturases and are much more closely related to the archetypal stearoyl-Coenzyme A-acting desaturase from rat than to the phospholipid-acting Delta12-desaturases widely reported in plants. Phylogenetic and functional analysis indicates the cricket AdD12Des gene may have evolved from an ancestral Delta9-desaturase. By contrast, the beetle Delta12-desaturase is distantly related to the cricket genes and beetle Delta9-desaturases suggesting evolution by an independent route. Linoleic acid has key physiological roles in insects and this is the first report of genes capable of producing this essential fatty acid in higher animals.

Ethyl formate is being evaluated as a fumigant for stored grain as it is a potential alternative to the ozone-depleting fumigant methyl bromide and to phosphine, which is under pressure owing to the development of strong resistance in stored grain insects. However, use of ethyl formate faces significant challenges, such as poor penetration through grain, significant losses to grain sorption, high concentrations of fumigant required to control insects, and flammability risks, which have limited its further development. In this study it was found that the combination of carbon dioxide (5-20%) with ethyl formate significantly enhanced efficacy of the fumigant against external living stages of the rice weevil, Sitophilus oryzae (L.), the lesser grain borer, Rhyzopertha dominica F., and the flour beetle, Tribolium castaneum (Herbst). Dynamic application of ethyl formate and carbon dioxide mixture (100 mg litre-1 ethyl formate, 20% CO2) pumped through a model silo containing wheat (50 kg) for one gas exchange was also investigated. A flow rate of 6 litres min-1 gave a relatively even distribution of fumigant throughout the grain column and similar mortality levels among cultures of S. oryzae and T. castaneum placed at three positions, the top, middle and bottom of the column. Mortality of 99.8% of mixed stage cultures of T. castaneum and 95.1% of S. oryzae was achieved in 3 h exposures to 111 and 185 mg ethyl formate h litre-1 respectively applied by the dynamic method. It is concluded that the combination of carbon dioxide with ethyl formate and dynamic application enhances distribution and efficacy of the fumigant against stored grain insects.

The defensive and bioactive polyacetylenic fatty acid, 8Z-dihydromatricaria acid, is sequestered within a wide range of organisms, including plants, fungi and soldier beetles. The 8Z-dihydromatricaria acid is concentrated in the defence and accessory glands of soldier beetles to repel avian predators and protect eggs. In eukaryotes, acetylenic modifications of fatty acids are catalysed by acetylenases, which are desaturase-like enzymes that act on existing double bonds. Here we obtained acyl Coenzyme A-linked desaturases from soldier beetle RnA and functionally expressed them in yeast. We show that three genes were sufficient for the conversion of a common monounsaturated fatty acid, oleic acid, to the 18 carbon precursor of 8Z-dihydromatricaria acid, that is, 9Z,16Z-octadecadiene-12,14-diynoic acid. These are the first eukaryotic genes reported to produce conjugated polyacetylenic fatty acids. Phylogenetic analysis shows that the genes responsible for 8Z-dihydromatricaria acid synthesis in soldier beetles evolved de novo and independently of the acetylenases of plants and fungi.

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