In South Africa the genus, Eucalyptus plays an important role as a major economic component in the forest and mining sector. Unfortunately, this genus has problems due to damage by pests. The Eucalyptus snout beetle, Gonipterus scutellatus, feeds and defoliates the leaves of eucalypts. Plants produce secondary metabolites, which protects them against defoliation by insects and herbivores. This study focuses on the variations of total soluble phenolic content of nine Eucalyptus species between the species and within the species throughout the year. Total soluble phenols were quantified with the Folin-Ciocalteau reagent. There was a general increase in the concentration of total soluble phenols throughout the year. The content of total soluble phenols were generally higher compared to carbohydrates. This experiment needs to be done on a continuous basis so as to formulate a screening method for eucalypt species that are resistant to G. scutellatus. / Dissertation (M Inst Agrar (Sustainable Insect Management))--University of Pretoria, 2005. / Zoology and Entomology / unrestricted

In South Africa, the genus Eucalyptus plays an important role as a plantation tree and hence forms a major economic component in the forest sector. An insect pest of these Eucalyptus species, Gonipterus scutellatus, causes periodic defoliation in the plantations. Plants have extraordinary array of chemicals (secondary metabolites), which defend them from herbivores. This study reports on the seasonal variation of the tannin concentration and carbohydrate content of the leaves of nine Eucalyptus species. Soluble tannins were quantified using Hagerman test and the carbohydrate content with a refractometer. Generally high tannin concentrations were observed during spring and late summer with low concentrations during autumn and winter. During the months of February, April, July tannin concentration was usually found to be higher than the carbohydrate content. The higher concentration of tannin could be linked to the allocation of carbon for the production of tannin instead of carbohydrates for growth. / Dissertation (MInst Agrar)--University of Pretoria, 2006. / Zoology and Entomology / unrestricted