Feldlaufer, M.F., U.S. Department of Agriculture, Agricultural Research Service, Insect Neurobiology & Hormone Laboratory, Tucson, Arizona, United States
Lusby, W.R., U.S. Department of Agriculture, Agricultural Research Service, Insect Neurobiology & Hormone Laboratory, Tucson, Arizona, United States
Weirich, G.F., U.S. Department of Agriculture, Agricultural Research Service, Insect Neurobiology & Hormone Laboratory, Tucson, Arizona, United States
Svoboda, J.A., U.S. Department of Agriculture, Agricultural Research Service, Insect Neurobiology & Hormone Laboratory, Tucson, Arizona, United States
Buchmann, S.L., Beltsville, Maryland, United States, Honey Bee & Insect Biological Control Laboratory, Tucson, Arizona, United States

Using high performance liquid chromatography in conjunction with radioimmunoassay and mass spectrometry, the major ecdysteroid of the solitary cactus bee, Diadasia rinconis, was determined to be 20‐hydroxyecdysone, with lesser amounts of makisterone A. Another 28‐carbon ecdysteroid thought to be the 24‐epimer of makisterone A was also detected. The neutral sterols of Diadasia consisted primarily of 24‐methylenecholesterol (92.2%) with lesser amounts of other C28 and C29 sterols. Cholesterol accounted for less than 0.1% of the total tissue sterols. The occurrence of 20‐hydroxyecdysone in a phytophagous hymenopteran is discussed in relation to the low level of cholesterol encountered. © 1993 Wiley‐Liss, Inc. Copyright © 1993 Wiley‐Liss, Inc.