THE ROLE OF AN EPIPHARYNGEAL SENSILLUM IN THE PERCEPTION OF FEEDING DETERRENTS BY LEPTINOTARSA-DECEMLINEATA LARVAE

An epipharyngeal taste sensillum in Leptinotarsa decemlineata larvae w as studied. Electron microscopy showed that the sensillum is innervate d by five neurons. Electrophysiological experiments showed that one of these cells responds to water, a second to sucrose and a third to two feeding deterrents that were also effective in a behavioural test. Re ceptor cells sensitive to feeding deterrents were not previously repor ted for L. decemlineata larvae or adults. The response of the sucrose- sensitive cell was strongly inhibited by one of the two feeding deterr ents and only slightly by the other feeding deterrent. The relationshi p between the behavioural and electrophysiological results is discusse d in order to elucidate the neural code of feeding deterrents in L. de cemlineata larvae. We conclude that probably both the response of the deterrent cell and peripheral interactions exerted by feeding deterren ts on the sucrose-sensitive cell determine the potency of feeding dete rrents. The present results provide a physiological basis for the hypo thesis that the presence or absence of feeding deterrents in potential food plants is a decisive cue in food plant selection by L. decemline ata larvae.