Susceptibility of Eucalyptus grandis and selected E. Grandis x E. Urophylla and E. Grandis x E. Camaldulensis hybrid clones to termite damage

Abstract

The growing of Eucalyptus hybrids has potential to reduce deforestation by lowering demand for other high-value tree species. However, tree growers and users have faced a challenge of making good choices of planting material due to high susceptibility of Eucalypts including Eucalyptus hybrid clones. This has been accelerated by scarcity of information in regards to termite susceptibility of Eucalyptus species. This study assessed the susceptibility of juvenile wood of Eucalyptus grandis and four Eucalyptus hybrid clones (GC 550, GC796, GC 796/2 and GU 7) against termite attack. The studied hybrid clones are the most commonly used species in Uganda in plantation forestry. Additionally, the wood consumption of two Central Uganda’s most prevalent termite species (Macrotermes bellicosus and Macrotermes subhyalinus) was evaluated to infer the species that is more destructive. Eucalyptus poles of one-year-old from Hoima district, Uganda were harvested and cross cut at breast height. These were air seasoned and plain sawn to wood stakes of 25 x 2 x 2 cm along the grain from the sapwood for termite tests. Samples were exposed to termite attack in an experiment set up at Kabanyoro village, Nangabo sub county in Wakiso district. Weight loss of different wood species due to termite attack was determined at the end of the exposure periods (2, 4 and 6 weeks). The results showed that Macrotermes bellicosus was more destructive to wood than Macrotermes subhyalinus. The mean weight loss was highest in Eucalyptus grandis (36.1g) and lowest in GU 7 (18.4g). Among Eucalyptus hybrid clones, susceptibility to termites increased in the order of GU7, GC796, GC550 and GC792/2 respectively. Therefore, GU 7 was the most resistant species where as Eucalyptus grandis was the most susceptible to termite damage. Termite activity in Eucalyptus wood increased with increase in exposure period from 2 to 4 to 6 weeks. Highly susceptible species (Eucalyptus grandis and GC 796/2) should not be planted is termite risk areas unless areas are fully treated against termite pests. More studies should be carried out to generate information about susceptibility of other Eucalyptus clones to termite attack.