ON THE SUSCEPTIBILITY OF EUCALYPTUS SPECIES AND CLONES TO ATTACK BY MACROTERMES-NATALENSIS HAVILAND (ISOPTERA, TERMITIDAE)

Eucalypt trees are notoriously susceptible to termite attack, especially by the fungus-growing termites (Macrotermitinae) of Africa and Indo-Malaysia. The planting of 'tolerant' species offers an alternative to the use of either persistent, but environmentally undesirable, insecticides or their non-persistent, but expensive, modern substitutes. This approach is particularly suited to rural development and reforestation programmes. The susceptibility to attack by Macrotermes natalensis Haviland of 33 Eucalyptus species, and 32 eucalypt clones, was ranked by tree mortality of each species and clone in five trials in areas of South Africa infested by this termite. The results were checked by two further trials which contained a number of different provenances of some of the eucalypt species. Eucalyptus dunnii was the most tolerant, followed by Eucalyptus macarthurii, Eucalyptus smithii and Eucalyptus viminalis in decreasing order. In general, tolerant or moderately tolerant species belonged to the subgenus Symphyomyrtus, the more tolerant to the section Maidenaria, series Viminales, subseries Bridgesiana. Susceptible species tended to belong to the subgenus Monocalyptus. Eucalyptus grandis constitutes 75% of commercial eucalypt plantings in South Africa and this species was very susceptible; but provenances of the same species from Zimbabwe were more tolerant than those from South Africa. Hybrid clones of the tolerant species, E. macarthurii, crossed with E. grandis, were susceptible; but two clones of E. macarthurii, one probably crossed with Eucalyptus camaldulensis and the other with an unknown species, were tolerant. Only one pure clone of E. grandis, and two of E. grandis x camaldulensis, were tolerant. Eight provenances of the most tolerant species, E. dunnii, seven of which were Australian, were not significantly different in their tolerances to attack by M. natalensis. There seemed to be no relation between the species reported in the literature as being tolerant to termite attack in native Australia (mostly belonging to the section Adnataria), and those found to be resistant to attack by M. natalensis in South Africa.