Selective sterol transfer in the honey bee: Its significance and relationship to other hymenoptera

The honey bee,Apis mellifera, is one of only a few species of phytophagous insects known to be unable to convert C-24 alkyl phytosterols to cholesterol. Regardless of the dietary sterols available to worker bees, the major tissue sterol of brood reared by the workers is always 24-methylenecholesterol, followed by sitosterol and isofucosterol. Normally, little or no cholesterol is present in honey bee sterols. The maintenance of high levels of certain sterols is accomplished through a selective transfer of sterols from the endogenous sterol pools of the workers to the developing larvae through the brood food material secreted from the hypopharyngeal and mandibular glands and/or the honey stomach of the workers. The selective uptake and transfer of radiolabeled C₂₇, C₂₈ and C₂₉ sterols have been studied to correlate these aspects of sterol utilization with the discovery of an unusual molting hormone (ecdysteroid) in honey bee pupae as the major ecdysteroid of this stage of development. The phylogenetic implications of this selective transfer phenomenon in the honey bee and comparison with sterol metabolism in certain other hymenopteran species emphasize the diversity of steroid biochemistry in insects.     

Neutral sterols of sawflies (symphyta): Their relationship to other hymenoptera

To investigate sterol utilization in sawflies, the neutral sterols of four species of sawflies were determined by gas-liquid chromatography and mass spectrometry, and compared to the respective dietary plant material. Cholesterol was the predominant (55–76%) sterol in all species and stages of sawflies examined. Host plants, however, contained primarily sitosterol (50–88%), along with other 24-alkylsterols and only 0.5–5.9% cholesterol, indicating that the sawflies examined are capable of dealkylating the C₂₈ and C₂₉ phytosterols in their diet to cholesterol. Comparative sterol metabolism in Hymenoptera is discussed.     

Change in teacher efficacy and student self- and task-related beliefs in mathematics during the transition to junior high school.

In a longitudinal study of 1,329 students and the teachers they had for mathematics before and after the transition to junior high school, the relation between students' beliefs in mathematics and their teachers' sense of efficacy is examined. Using repeated measures multivariate analysis of variance (MANOVA), we found that the rate of change within the school year in students' expectancies, perceived performance, and perceived task difficulty in math differed at Year 1 and 2, depending on teacher efficacy before and after the transition. Students who moved from high- to low-efficacy math teachers during the transition ended the junior high year with the lowest expectancies and perceived performance (even lower than students who had low efficacy teachers both years) and the highest perceptions of task difficulty. The differences in pre- and posttransition teachers' views of their efficacy had a stronger relationship to low-achieving than to high-achieving students' beliefs in mathematics. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neutral sterol metabolism in insects

Since they are unable to biosynthesize sterols, many phytophagous and omnivorous insects satisfy their cholesterol requirement by side chain dealkylation of the C-24 alkyl group of dietary C₂₈ and C₂₉ phytosterols. However, not all insects that can dealkylate the phytosterol side chain produce cholesterol. In addition, certain insects,e.g., some Hymenoptera, Hemiptera, and Diptera, are unable to dealkylate the sterol side chain. Although C₂₇ ecdysteroids (molting hormones), which are biosynthesized from cholesterol, are the major ecdysteroids in most insects, many of those species that are unable to dealkylate phytosterols utilize campesterol as a precursor for the C₂₈ ecdysteroid makisterone A. The considerable diversity of steroid utilization between certain insect species makes it difficult to generalize about insect steroid biochemistry. The ability to disrupt certain unique aspects of steroid utilization and metabolism in insects might be exploited for developing new insect control technology. Based on a paper presented at the Symposium on Plant and Fungal Sterols: Biosynthesis, Metabolism and Function, held at the AOCS Annual Meeting, Baltimore, MD, April 1990.     

The fate of radiolabeled steroids in ovaries and eggs of the tobacco hornworm,Manduca sexta

To determine the precursors and the fate of 26-hydroxyecdysone in eggs, the fate of labeled putative ecdysteroid precursors was examined in the tobacco hornworm,Manduca sexta. Following injection of [¹⁴C]cholesterol, 22,25[¹⁴C]dideoxyecdysome or [³H]ecdysone into female pupae (day 16), only [¹⁴C]cholesterol was incorporated and metabolized. It was converted to labeled nonecdysteroid and ecdysteroid conjugates, of which the latter in ovaries and 48- to 64-hr-old eggs is mainly 26-hydroxyecdysone 26-phosphate (>85% in ovaries). Quantitation of the ecdysteroid conjugate by reversed-phase high performance liquid chromatography (RP-HPLC) showed that the levels of 26-hydroxyecdysone 26-phosphate were 31 μg/g of ovaries from 4-day-old females and 25 μg/g and 17 μg/g of 48- to 64-hr-old and 72- to 88-hr-old eggs, respectively. The RP-HPLC of the conjugate fraction of 48- to 64-hr-old eggs showed an additional peak of radioactive material eluting about three min before the 26-hydroxyecdysone 26-phosphate. The quantity of this material increased in the 72-to 88-hr-old eggs, though it was not detected in the analyses of the conjugate fraction from ovaries. Additional peaks of radioactive material eluting before the 26-hydroxyecdysone 26-phosphate peak were observed in the chromatogram of the conjugates of 72- to 88-hr-old eggs. These radioactive materials need to be identified to determine the ultimate fate of ecdysteroids in the developing embryos of the tobacco hornworm. No radioactive free ecdysteroids were detected in either egg age group.     

Pollen sterols from three 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, 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 cholesterolvia dealkylation.