Wood - Consumption Rate and Survival of the Formosan Subterranean Termite

Abstract

Redwood and cedar were the most resistant or least preferred woods of the 6 wood species fed to the Formosan subterranean termite. Significantlymore Ponderosa pine, spruce, hemlock and Douglas fir were consumed than redwood or cedar. There were no statistically significant differences in consumption between redwood and cedar and no significant differences in the amounts of the other 4 wood species consumed. Both redwood and cedar apparently were not completely suitable food for the termites. 100% of the termites fed redwood died within 3 weeks and approximately 50% of those fed cedar died in the same period. Termites are major pests of wood and wood products in tropical environments. The Formosan subterranean termite, Coptotermesformosanus Shiraki, is the most important insect pest in Hawaii. It causes significant damage to buildings, trees, plants, utility poles, etc. In addition, the cost of controlling this termite in Hawaii has been steadily increasing. This has been due in part to increases in the cost ofconstruction and the concomitant increase in costs of repair. However, the main reasons for the increase have been due to: (1) the spread of this species within the state into areas where it previously did not occur, (2) the increase in the population density of C. formosanus in areas where it did occur, and (3) the increase in the number of structures at risk. Beal (1967) first estimated the damage caused by this termite at 2-3 million dollars a year. Ten years later, this figure increased almost tenfold (Lai 1977). In 1981, Higa estimated that the cost ofprevention, control and repair ofdamage caused by C. formosanus exceeded 20 million dollars a year. More recent data indicates that Higa's estimates were low and the actual costs may exceed SO million dollars a year. The relatively high costs incurred in Hawaii is in part due to the fact that (1) conditions in Hawaii are favorable for the termite, (2) almost all of the single family homes are of wood frame construction and (3) much of the wood used apparently is highly susceptible to attack by C.formosanus. In qualitative tests, redwood was found to be the most resistant of 14 woods to decay and insect attacks in ground and above-ground tests in humid residential areas on Oahu (Skolman 1974). The suscep tibility ofthe woodscommonly used in construction in Hawaii, however, has not been compared and quantified. Douglas fir, Pseudotsuga menziesii (Mirb.) Franco, is the most frequently used wood in construction in Hawaii, in part because of its ready availability, physical strength, and ease with which it can be handled. According to Wilcox (1984), however, the popularity of Douglas fir in the Hawaiian market does not only reflect the consumers' demands but also is the result of the interaction of complex commer cial and political forces in Hawaii. Unfortunately, Douglas fir heartwood is extremely 'Journal Series No. 2939 of the Hawaii Institute of Tropical Agriculture and Human Resources. 'Department of Entomology, University of Hawaii, 3050 Maile Way, 310, Honolulu, Hawaii 96822. Present address: FL Lauderdale Research and Education Center, University ofFlorida, 3205 College Ave., Ft Lauderdale, FL 33314. 110 Proceedings, Hawaiian Entomological Society difficult to penetrate with wood preservatives so that treatment does not guarantee protection against attack by Cformosanus. Sapwood can be penetrated but does not have the structural strength ofheartwood. In addition, spring wood ofDouglas fir was found to be attractive to Cformosanus (Fujii 1975). Studies have shown that each species of termite has its own preferences for different wood species (Ruyooka and Groves 1980). Smythe and Carter (1969) fed Reticutitermesflavipes (Kollar) 11 native wood species used commercially in the U.S. and found that the termites did poorly on redwood, Sequoia sempervirens (D. Don) Endl., baldcypress, Taxodium distichum (L.) Rich., and black walnut, Jugulansnigra L. (Bultman et al. 1979) indicated that some tropical African woods were resistant to the attack by C formosanus. The resistance may be due to the physical (Behr et al. 1972) or chemical properties ofthe wood (Kofoid and Bowe 1984, Rudman and Gay 1967, Carter et al. 1975, Carter et al. 1983), or to the species of termites, or to the symbiotic protozoa (Carter et al. 1981). The results of these studies have lead to proposals to use the wood's natural resistance to protect structures from termite attack (Bultman et al. 1979). This study was initiated to measure the resistance of 6 woods commonly used in construction in Hawaii to attack by Cformosanus to suggest possible alternatives to the current use patterns in Hawaii. MATERIALS AND METHODS Experimental Boards of Douglas fir, redwood, Ponderosa pine (Pinus ponderosa Dougl. ex Laws.), Engelmann spruce (Picea engelmannii (Parry) Engelmann), Western hem lock (Tsuga heterophylla (Raf.) Sarg) and Western red cedar (Thujaplicata Donn), were obtained from a commercial lumber yard in Honolulu. Blocks 1.8 x 1.8 x 1.8 cm were cut from a single board of each species, oven dried at 90°C for 48 hours and weighed. Each block was placed in a screw-topjar (5.5 cm in diameter by 6.5 cm in height) and covered by 50 ml ofcoral sand moistened with 10 ml ofdeionized water. Two-hundred field collected termites (170 "workers," undifferentiated larvae of at least the 3rd instar and 30 soldiers) were introduced into each unit and stored at 29 ± 1°C. The average weight ofthe workers was determined by weighing 5 groups of 10 termites each and calculating the mean. Eighteen experimental units were prepared for each wood species. At weekly intervals 3 units ofeach wood species were selected at random and disassembled. The surviving termites were counted and wood blocks were cleaned, oven dried, and reweighed. Data Analysis Su and La Fage (1984a,b) found that there were two patterns of mortality in the termites in the feeding trials. In one type, most of the mortality occurred in the first three weeks. Very few termites died in the second three weeks. In the second type, mortality increased linearly and reached 100% before the experiment was terminated. In this study, levels at which mortality stabilized after three weeks were compared among treatments. Treatments in which all of the termites died in six weeks were excluded from the analysis. The computation method for wood-consumption rate was similar to that des cribed by Su and La Fage (1984a). A linear mortality model was used to correct for cumulative mortality. Thus, wood-consumption rate (WCR), mg wood/g termite/ day, for each sampling date was calculated using the following equation: WCR = 2(W1 W2)/(a*t(170+Nt))

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@inproceedings{Tamashiro2008WoodC, title={Wood - Consumption Rate and Survival of the Formosan Subterranean Termite}, author={Minoru Tamashiro}, year={2008} }