Chemosensory basis for feeding behaviour differences in the larvae of two closely related butterfly species: Papilio hospiton, a specialist and Papilio machaon, a generalist

The spike activity of the medial (M) and lateral (L) maxillary styloconic taste sensilla of two genetically close species of lepidopterous larvae (Papilio machaon and Papilio hospiton, oligophagous and monophagous, respectively), was recorded after stimulation with deterrent (NaCl at high concentration and nicotine) and phagostimulant compounds (sucrose, glucose, fructose and myo-inositol), with the aim of comparing their response patterns in the light of their different feeding choices. The results show that the spike responses of the maxillary sensilla of two species are statistically different. The neurons activated by phagostimulant or deterrent stimuli are the same in both species and for both sensilla, but P. hospiton shows a higher sensitivity with respect to P. machaon. Finally, the activation of neurons responding to phagostimulants in P. machaon inhibits the neurons responding to deterrents even at low concentrations but, in P. hospiton, only at high concentrations. In conclusion, the higher sensitivity of P. hospiton with respect to P. machaon can justify the differences in feeding behaviour.