Acetonitrile (methyl cyanide) emitted by the African spider plant (Gynandropsis gynandra L. (Briq)): Bioactivity against spider mite (Tetranychus urticae Koch) on roses

The African spider plant (Gynandropsis gynandra L. (Briq)) has repellent properties against spider mite on roses (Rosa hybrida L.) when grown as a companion plant. Gas chromatography–mass spectrometry (GC–MS) has been used to identify potential volatile compounds in the foliar emissions of this plant that may contribute to the anti-mite properties. Acetonitrile (methyl cyanide) was the most abundant compound emitted by entire plants and detached leaves of five lines of both glasshouse- and field-grown G. gynandra, with only trace levels emitted by roses grown under similar conditions. A toxicity bioassay was conducted to evaluate the bioactivity of acetonitrile against spider mite, and ≥2.5 μL/L of air rendered 100% of the mites inactive. Removal of the compound after an initial exposure of up to 5.0 μL/L of acetonitrile allowed some 10% of the mites to recover mobility, but above this level no mobility was observed. This study provides a very strong indication that foliar emissions of acetonitrile by G gynandra are responsible, to a significant degree, for the spider mite repellent activity of the plant when used as an intercrop with roses.

Research highlights
► Gynandropsis gynandra L. (Briq) has repellent properties against spider mite on roses.
► Acetonitrile is the major volatile emitted by G. gynandra L. (Briq) and not roses.
► Depending upon the concentration, acetonitrile can be repellent or toxic to spider mites.
► Emitted acetonitrile from G. gynandra is a major factor in repelling spider mite.