Phytosterol structure and its impact on feeding behaviour in the generalist grasshopper Schistocerca americana

Sixth-stadium nymphs of the grasshopper Schistocerca americana (Drury) (Ort hoptera: Acrididae) were observed in a series of experiments designed to me asure feeding behaviour in response to suitable and unsuitable phytosterols . In the first experiment, grasshoppers were presented with artificial diet that contained either sitosterol. a suitable phytosterol, or a spinach lip id extract which contained only unsuitable sterols as well as other spinach lipids. The diet with the spinach lipid extract, but not the sitosterol di et, evoked a deterrent response. To determine if the spinach sterols were r esponsible for the deterrent response, a second experiment was performed wh ere the spinach lipid extract was separated into three lipid classes, inclu ding desmethyl sterols, dimethyl sterols and the remaining spinach lipids. Grasshoppers presented with artificial diet containing the desmethyl sterol s (the end-product sterols in spinach) exhibited deterrent responses. Final ly, feeding behaviour to a suite of different sterols, including cholestero l (suitable), stigmasterol (unsuitable), and lathosterol (unsuitable), was observed; these sterols were selected because they show variation in the po sition of double bonds. Grasshoppers presented with diets containing unsuit able sterols again exhibited deterrent responses. Overall, the deterrent ef fect was strongest when sterols with a double bond at position 22 were in t he diet.