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Secondary Plant Compounds as Feeding Deterrents in the African Subterranean Termite Schedorhinotermes lamanianus Sjöstedt (Isoptera: Rhinotermitidae): A Behavioural and Neurophysiological Approach
(2010)
- In the present study, the influence of plant-derived secondary compounds on feeding behaviour in the subterranean termite Schedorhinotermes lamanianus was investigated. Furthermore, the chemosensory input system responsible for the perception of these compounds was investigated using electrophysiological methods. The obtained results provide evidence that in S. lamanianus a variety of structurally diverse secondary plant compounds (alkaloids and non-alkaloids) other than securinega-alkaloids influence feeding behaviour. These compounds evoke an avoidance of food sources or lower food consumption under choice conditions even at lower concentrations obtained for securinega-alkaloids. Furthermore, these compounds also reduce feeding under no-choice conditions. Termites seem to ingest less food even when they started feeding and no alternative food source is available. Therefore these compounds act as repellents and feeding deterrents in S. lamanianus depending on the test conditions under which they are applied. Furthermore, the present study provides strong evidence that different proximate mechanisms explain feeding inhibition in S. lamanianus: 1) Twelve structurally very diverse alkaloids, including feeding deterrent alkaloids in S. lamanianus, stimulated the taste neuron II/3 in TP II sensilla on antennae of this termite species. Non-alkaloids did not stimulate neuron II/3. Therefore, this neuron II/3 is an "alkaloid cell" negatively influencing feeding behaviour in this termite. 2) Feeding inhibition seems also to be influenced by the inhibition of phagostimulant taste neurons ("water cells") on antennae. 3) A second sensory input system for the perception feeding deterrent plant-derived secondary compounds seems to be evident as some tested compounds (alkaloids and non-alkaloids) are clear antifeedants in S. lamanianus but do not influence feeding behaviour by the former two mechanisms. Hence, in termites feeding inhibition by secondary plant compounds is a very complex process which needs further investigation. Including neurophysiological investigations of the chemosensory input system seems to be a promising approach to better understand feeding inhibition in termites which may lead to improved wood protection and termite management.
