Post-ingestive feedbacks and associative learning regulate the intake of unsuitable sterols in a generalist grasshopper

Behavioural studies of the grasshopper Schistocerca americana were undertak en to identify the mechanisms that regulate the intake of dietary sterols, In the first experiment, grasshoppers were allowed to feed on spinach, a pl ant containing only unsuitable sterols; immediately after this first meal, a suitable or unsuitable sterol was injected into the haemolymph, Grasshopp ers injected with unsuitable sterols had second meals on spinach that were significantly shorter than those of grasshoppers injected with suitable ste rols, indicating that unsuitable dietary sterols are detected post-ingestiv ely, In the second experiment, grasshoppers were fed food containing only u nsuitable sterols and were then presented with glass-fibre discs containing different concentrations of a suitable sterol or sucrose only (the control ). The results suggest that grasshoppers do not use a direct feedback opera ting on mouthpart chemoreceptors to regulate their intake of suitable stero ls, In the third experiment, grasshoppers were presented with artificial di ets containing different sterols and flavours, and feeding was observed ove r a sequence of meals. The results from both the first and last experiments suggest a role for associative learning in regulating the intake of unsuit able sterols.