Volatile components of ripe fruits of Morinda citrifolia and their effects on Drosophila

The only larval resource of the specialist species, Drosophila sechellia, is ripe fruits of Morinda citrifolia. The chemical composition of this fruit, which is very toxic to most Drosophila species, was investigated and 51 compounds were abundant enough to be identified by GC-MS. The ripe fruit is characterized by a large amount of carboxylic acids, especially octanoic and hexanoic acids. The biological effects of the ripe fruit and its main acids were investigated with behavioural studies. Octanoic acid is responsible for the general toxicity of the fruit to most Drosophila species; D. sechellia is the only species which is resistant to this acid. Hexanoic acid has a unique effect, causing reversible coma but no mortality. Decanoic acid is inactive. A mixture of these three acids in proportions similar to those found in the fruit, mimics the effects of ripe fruits of M. citrifolia.