Sterol metabolic constraints as a factor contributing to the maintenance of diet mixing in grasshoppers (Orthoptera : Acrididae)

Sterols are essential nutrients for all arthropods, including grasshoppers, but metabolic constraints may limit which sterols can support normal growt h and development. In the firsts part of this study, a comparative experime nt, which included five different species of grasshoppers (Orthoptera: Acri didae) representing three separate taxonomic groups, was performed to deter mine how widespread sterol metabolic constraints are within the Acrididae. Grasshoppers were reared on artificial diets containing sterols that differ ed in the position of double bonds within the sterol structure, and various life history traits were measured. Sterols with double bonds at position 7 , within the sterol nucleus, and/or at position 22, on the cholestane side chain, failed to support development to the adult stage for any of the five species. In addition, grasshoppers reared on sterols with these configurat ions often had extended developmental times and reduced growth rates in the first and second stadium compared with grasshoppers reared on sitosterol o r cholesterol diets. In the second half of this study, we examined how mixt ures of suitable and unsuitable sterols influenced survival, growth, and de velopment. Artificial foods containing mixtures of suitable and unsuitable sterols were fed to the highly polyphagous grasshopper Schistocerca america na. Results suggest that survival and performance of this grasshopper suffe r as the concentration of unsuitable sterols increases and as the ratio of suitable to unsuitable sterols in the diet decreases;We review the literatu re to document variation in plant sterol profiles and propose that constrai nts on sterol metabolism may contribute to the maintenance of diet mixing i n the Acrididae.