Chemical defence in thrips

The production of volatile substances by a single species of Thysanoptera was noticed long ago by HODSON (1935) as “a pungent and distinctive but not unpleasant odour”. During the last three decades there have been more than 30 papers dealing with secretions by thrips. It was noticed that several thrips species raise and lower their abdomen with a drop of certain kind of fluid on the abdominal tip when they are attacked by an enemy (LEWIS 1973). The secretion reservoir seems to be the hindgut (HOWARD et al. 1983). Some of the complete secretions, as well as single components, eg. lactones like mellein, were found to be ant repellents (BLUM 1991, BLUM et al. 1992, HOWARD et al. 1983). Further they may function as contact irritants, alarm pheromones, or in some cases, fumigants. Thrips produce a great variety of substances including alkanes, alkenes, alkanoic and alkenoic acids, aliphatic and cyclic esters, monoterpenes and aromatic compounds (reviews in BLUM 1991, TERRY 1997). Some authors investigated only whole thrips, but not the single allomone droplets. The presented paper deals with defensive secretion used by Suocerathrips linguis MOUND & MARULLO 1994. The droplets of S. linguis secretion were collected with a fine capillary tube, dissolved, treated with derivatives if necessary, and analysed by gas chromatography coupled with mass spectrometry. They contain esters of acetic acid and long chained saturated and unsaturated alcohols (C16 .. C20) as main components (Fig. 1, peaks from17.11 to 19.82). The components have a very high boiling point. One of the saturated esters is solid at room temperature. There are no differences in the mixture between male and females, and the secretion does not contain any compound from the fungi on which the thrips feed or from the host plant (Sansevieria). Sex specific concentrations of monoterpenes (fig. 2, peak at Chemical defence in thrips