POLLEN STEROLS FROM 3 SPECIES OF SONORAN CACTI

Cactus bees are important pollinators that contribute to the long-term stability of arid regions in the United States. Since all insects are dependent upon a dietary source of sterol for normal growth, developm ent and reproduction, a study was undertaken to determine neutral ster ols available to cactus bees. The total neutral sterol composition of hand-collected pollen was determined for three species of Sonoran cact i by gas-liquid chromatography and mass spectrometry. 24-Methylenechol esterol was the predominant pollen sterol in Engelmann's prickly pear, Opuntia phaeacantha, cholla, O. versicolor, and cardon, Pachycereus p ringlei. Two pentacyclic triterpene alcohols, lupeol and moretenol, we re also isolated. Since no cholesterol was detected in any of the poll en samples, cactus bees would have to utilize the 24-alkyl sterols unc hanged or convert these sterols to cholesterol via dealkylation.