Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2000
Publication Date: 8/1/2000
Citation: Shapiro, J.P., Bowman, K.D., Lapointe, S.L., Ghiviriga, I. 2000. Dehydrothalebanin, a source of resistance from glycosmis pentaphylia against the citrus root weevil diaprepes abbreviatus. Journal of Agricultural and Food Chemistry. Interpretive Summary: The citrus root weevil Diaprepes abbreviatus does over $700,000 in estimated damage to citrus each year. Development of a weevil-resistant citrus rootstock - the root system onto which the fruit-bearing portion of a citrus tree is grafted - would help protect citrus trees from this extensive damage. Although existing citrus rootstocks are shown to exhibit little resistance, we have identified a relative of citrus, Glycosmis pentaphylla or orangeberry, as highly resistant and identified a natural product responsible for resistance. Larvae that were fed on G. pentaphylla roots on live plants exhibited greatly reduced growth and increased mortality. Ground roots were tested against larvae by mixing them with an artificial larval diet. Larval growth was inhibited and mortality increased in relation to the concentrations of roots in diet. Using this test, we isolated, purified, and identified a chemical constituent of G. pentaphylla roots, dehydrothalebanin B, that is at least partially responsible for the observed resistance. In addition, a chemical insecticide, dieldrin, was identified as a contaminant of at least some of the roots used in the isolation.
Technical Abstract: Roots of a citrus relative, Glycosmis pentaphylla (orangeberry), have been shown to inhibit the growth and survival of larvae of the citrus root weevil Diaprepes abbreviatus. Here, G. pentaphylla root extracts were shown to be active. Identifications of an active phytochemical, dehydrothalebanin B, and a contaminating insecticide, dieldrin, are described. Roots of G. pentaphylla were incorporated into the diet of D. abbreviatus. Growth of neonate larvae was inhibited in relation to the concentration of roots, while roots of citrus rootstocks and their hybrids produced negligible growth inhibition. An acetone extract of roots from G. pentaphylla was active when incorporated into diet, and diet incorporation was used to guide fractionation of the extract. Month-old larvae were placed on diet containing the fractions, and their growth was measured following a 28-d ingestion period. Three major fractions from silica open-column normal-phase chromatography (LPLC) were active. Using semipreparative normal-phase HPLC, active components were isolated from each of these fractions. Only one HPLC subfraction from each of the three active LPLC fractions was active, and two individual components among the three subfractions were identified by GC-MSD. Preparative normal-phase HPLC, tracked by GC-MSD, was used to isolate two active compounds. One was identified by GC-MSD and NMR as the amide dehydrothalebanin B. Following a second HPLC fractionation step and bioassay, the other active compound was identified by GC-MSD as dieldrin, a chlorinated hydrocarbon insecticide whose origin in our samples is uncertain.