Four Week Termite Test of Hibiscus elatus (Blue Mahoe) Sapwood and Heartwood Against Feeding by the Eastern Subterranean Termite Reticulitermes flavipes (Kollar)
Methods
No-choice termite test
Wood blocks of H. elatus sapwood and heartwood in addition to southern pine controls were cut to about 25.4 mm square by 6.4 mm (n=5). All blocks were dried in an oven at 40ºC overnight, weighed, and conditioned at 27oC to a 12.9% equilibrium moisture content prior to being subjected to a termite bioassay according to a no-choice test procedure (ASTM 1998c). Each block was placed in a lidded-test dish with 50 g sand, 8.5 mL DI water and 1g termites. Dishes were incubated at 27oC and 80% RH for 4 weeks. After four weeks, blocks were removed from the dishes, cleaned, dried, re-conditioned and weighed to determine weight loss. A visual rating of attack was recorded for each block.
Results
Visual ratings are based on a 10-point scale: 10 being sound wood and 0 being complete failure (AWPA 2003). Sapwood of H. elatus had an average visual rating of 9, while the heartwood had an average rating of 9.2 (see figure 1). A rating of 9 signifies slight attack, with up to 3% of cross sectional area being affected. Control Southern yellow pine blocks had an average visual rating of 0, signifying complete failure. Mass losses observed also showed minimal damage to the blocks, though heartwood is significantly more resistant to termite feeding than is the sapwood (see table 1). No mortality was observed in any of the groups.
Figure 1: Test Blocks
Table 1: Mass Loss and Visual Rating
Discussion
Results showed H. elatus to be a very resistant wood species to feeding by R. flavipes. Though the wood did not appear to cause any mortality, this may be due to reduced feeding rather than lack of toxicity. Other termite species may show different results than occurred here.
References
Arango, R.A., Green, F., Hintz, K., Lebow, P.K. & Miller, R.B. (2006) Natural durability of tropical and native woods against termite damage by Reticulitermes flavipes (Kollar)
International Biodeterioration & Biodegradation 57: 146-150.
American Society for Testing Materials. (1998c) Standard test method for laboratory evaluation of wood and other cellulosic materials for resistance to termites. D345-74. In: Annual Book of Standards, Vol. 04.01. ASTM, West Conshohocken, PA. pp. 430-432.
AWPA (2003) Standard method of testing wood preservatives by laboratory soil block cultures E10-01. In: Annual Book of AWPA Standards, American Wood Preservers’ Association, Selma, Alabama, USA, pp. 419-429.
Experiment carried out for Tropic Ventures, Nov/Dec 2006 by :
Rachel Arango
Biological Laboratory Technician,
USDA Forest Products Laboratory
