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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, development and reproduction, a study was undertaken to determine neutral sterols available to cactus bees. The total neutral sterol composition of hand-collected pollen was determined for three species of Sonoran cacti by gas-liquid chromatography and mass spectrometry. 24-Methylenecholesterol was the predominant pollen sterol in Engelmann’s prickly pear, Opuntia phaeacantha, cholla, O. versicolor, and cardon, Pachycereus pringlei. Two pentacyclic triterpene alcohols, lupeol and moretenol, were also isolated. Since no cholesterol was detected in any of the pollen samples, cactus bees would have to utilize the 24-alkyl sterols unchanged or convert these sterols to cholesterol via dealkylation.