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AMERICAN WOOD-PRESERVERS' ASSOCIATION 1988 Resistance of ACZA Treated Douglas-Fir Heartwood to the Formosan Subterranean Termite
Professor Robin Yamamoto, and
Research Associate Department of Entomology, University of Hawaii Honolulu, Hawaii There is no current wood treatment available that can effectively protect Douglas-Fir heartwood against the Formosan subterranean termite, Coptotermes formosanus Shiraki. This is a serious problem m Hawaii because Douglas-Fir is the major construction lumber used in the state and the Formosan subterranean termite is well established here. These laboratory and field tests were conducted to determine whether ACZA (Chemonite) could protect Douglas-Fir heartwood against the Formosan subterranean termite. For the laboratory tests, blocks which had been treated with ACZA to five levels of retention from 0.11 to 0.62 pounds per cubic foot were tested using a modification of the ASTM D:3345-74 (Reapproved 1980) method. None of the treated blocks were attacked. Even the lowest retention 0.11 gave complete protection. In the field tests, treated Ix4xlO's at retention levels of 0.1, 0.2, 0.4 and 0.6 were combined with untreated I x 2X lO's and placed directly into a strong field colony of C formosanus. The untreated wood was destroyed but the ACZA treated wood was untouched. In these tests, ACZA completely protected Douglas-Fir heartwood from attack by the Formosan subterranean termite. Keywords: Formosan subterranean termite, ACZA, Chemonite, CCA, Douglas
Fir, termiticides, probit analysis, toxicity protection. The Formosan subterranean termite, Coptotermes formosanus Shiraki, was accidentally introduced into Honolulu in the 1860's and had spread to all the major islands in the State. It is now the single most economically damaging pest in Hawaii. It is estimated to cost over $50 million a year to prevent infestations or to control attacks by this pest when prevention fails (Tamashiro, et al., 1987). The Formosan will feed on anything with cellulose. A mature colony can cause a tremendous amount of damage in a very short time. Unprotected homes built over strong colonies have been almost destroyed in 2 years. The termite has attacked structures from single family dwellings to 40 story high rises from basement to roof. The termite also attacks telephone poles, boats, paper, cloth, fruits, plants, trees, etc. (Lai et al., 1983). The current world distribution of this pest now includes: China, Taiwan, Japan, Guam, Midway, Hawaii Sri Lanka, South Africa, and the continental United States including Texas, Louisiana, South Carolina, Florida, Mississippi, Alabama and Tennessee (Su and Tamashiro, 1987). The distribution of this termite has dramatically increased in the last 20 years. There are two basic strategies used to manage this pest. These are prevention and remedial control. Remedial control of the Formosan subterranean termite is extremely difficult because there are more than 2 million termites in an average colony and a colony may extend more than 350 ft from end to end (Tamashiro, et al., 1980). It is virtually impossible to treat and eradicate the entire colony. Prevention, therefore, is extremely important in the management of this pest. One of the methods used in prevention is to treat wood with a preservative which can protect it against attack. In Hawaii, Douglas-Fir, the most commonly used construction lumber, and one that is highly susceptible to attack by the Formosan subterranean termite (Su and Tamashiro, 1986), is pressure treated with CCA. Unfortunately, CCA cannot penetrate Douglas-Fir heartwood deep enough to form an effective barrier. The penetration is so shallow that even minor checking exposes untreated wood. Moreover, colonies of the Formosan subterranean termite can penetrate the thin layer of CCA deposited on the surface and destroy the piece. At present, there is no adequate wood preservative that can penetrate Douglas-Fir heartwood deep enough to protect it against the termite. A new, more effective material is required. These laboratory and field tests were conducted at the University of Hawaii to determine whether ACZA could protect Douglas- Fir against the Formosan subterranean termite. Return to the top.
The laboratory was kept at 72ø F (22.2ø C) and 5967 percent relative humidity. The blocks were then placed individually in jars measuring 77mm in diameter and 88mm in height. Twenty ml of sand sifted through U.S.A. Standard Testing Sieve No. 14 (A.S.T.M.E.-11 Specification) which has a pore diameter of 1.4mm were poured over the block. This was a sufficient amount of sand to bury the block but still leave the upper surface exposed. Six ml of distilled water were added to each jar before adding the termites. The termites were collected from a highly active field colony on the day that the test was initiated using a technique modified from that developed by Tamashiro et al. (1973). Two ml of termites, which contained approximately 288 workers, 48 soldiers and 2 nymphs, were introduced into each jar. The jars were held in an incubator at 29ø C. The blocks were examined at least twice a week to estimate termite mortality, and to observe the location and behavior of the termites. The tests were terminated after 3 weeks because all of the termites feeding on treated blocks died. The blocks were carefully cleaned, dried and reweighed. The field experiments were conducted by placing treated wood directly into a strong colony of the Formosan subterranean termite. The Douglas-Fir heartwood used in these tests was from the Willa mette Valley of Oregon and was so identified by a WCLB stamp. Incised commercial S4S, 1X4 by 8' Douglas-Fir heartwood with a ring count of 6 to 10 per inch were treated with ACZA to retentions of 0.10, 0.25, 0.40, and 0.60 pounds per cubic foot (pcf). The preparation of the samples and subsequent treatment was performed in accordance with AWPA M7-83 Standards except that Douglas-Fir heartwood was used instead of southern pine sapwood. The treated wood was 100 percent penetrated as judged by arsenic and copper stains (AWPA A3) applied to sections instead of borings. Untreated pieces which were used for controls came from the same batch of lumber. Both treated and untreated wood were cut into 10" lengths for use in the test. Fifteen untreated 1 X 4 X 10" were selected at random from the 36 pieces available and were ripped to 1X2X10". The samples, treated and untreated, were left to hydrate and reach equilibrium in the laboratory. The test pieces were weighed for several consecutive days until the weights reached a stable range. The variations in laboratory conditions increased or decreased the weight of the wood by 34 percent. Rectangular traps or test boxes, 4x;4x10", were constructed using two treated 1 X4X 10" of the same retention and two untreated 1x2x10" (Figure 1). These traps were placed directly into a strong colony of the Formosan subterranean termite. The test traps were placed vertically so the cut ends fitted directly over the termite galleries. Paper toweling was placed in the center of each trap to facilitate attack. The traps were covered with an untreated 1x4x4" to keep the hollow center moist and covered. Control traps were constructed in a similar manner with untreated wood. There were three replications for each retention level. The colony selected for the test was located on the campus of the University of Hawaii, Manoa. The colony had been monitored for several years. It was a strong, vigorous colony with approximately 4 million large active termites. The experiment was terminated after 18 weeks because the termites left the traps after they ate the untreated wood. The wood was cleaned, dried and allowed to stabilize to room conditions and weighed. Return to the top.
 Results and Discussion Laboratory test
The treated blocks, at all retention levels tested, were sufficiently toxic to kill all of the termites in the test. The rate of mortality, at least until the 10th day, seemed to be directly related to the retention levels. The 0.31 level was an exception. The 0.31 level killed the termites faster than at any other concentration. The reason for this anomaly is not known. The termites did not eat any more of the 0.31 wood than at any other retention level. In fact, most of the blocks with the 0.31 retention increased in weight by 0.01 grams (Table 1). The average showed no change because the data was rounded off to two places. The slight increase or decrease in weight of the wood was probably due to small variations in humidity and / or to specks of dust that may have clung to the blocks. A probit analysis of the data using time instead of dosage revealed that there were significant differences in the LT50's (the time it took to kill 50% of the termites) among the retention levels although total mortality was achieved in about the same time (Figure 1). Table 2 presents LT50's, their fiducial limits and the equations for the lines. The LT50 for the 0.31 concentration was reached earlier than at any other concentration. There were no differences in the LT50's between 0.11 and 0.20 and between 0.41 and 0.62 pcf. The speed of kill of the termites by ACZA indicates that it is a Type III material in the classification of termiticides by Su et al. (1982). Type III toxicants are slow acting, non-repellent materials. These are the only type of toxicants which can be used m the remedial control of the Formosan subterranean termite with any chance of eradicating the colony. It is the only type which will not evoke a defensive response from the colony. Type III materials are slow acting so that they will allow the termites to move to other parts of the colony before they die. Type I materials are repellent and Type II materials kill quickly so that the termites die in the treated area. In both instances, the treated area is sealed off so that there is no further contact with the toxicant. The termites were not observed feeding on the ACZA treated wood. In addition, careful visual examinations of the treated blocks after the termination of the experiment, revealed no evidence of feeding. The termites themselves also did not show any direct evidence of feeding. The termite is sufficiently transparent so that if it had fed to any extent on a dark substrate such as the ACZA treated wood, the material would have been visible in the termites gut. The gut would have shown up as a dark tube in the termite.
The pre and post test weights of the blocks also did not reveal any evidence of feeding (Table 2). One treated block lost 0.02 grams, 9 lost 0.01 grams, 5 showed no change and 10 gained 0.01 grams. The data was unusual in that there seemed to be a tendency for the blocks with low retention to gain weight and those with high retention to lose weight. It was not known, however, whether the gain or loss in weight represented true differences or random variations which appeared consistent. The variations, plus or minus 0.01 grams, were well within normal variations for this type of experiment. Feeding, however, must have occurred for the termite to acquire the toxicant. ACZA is a stomach poison with no contact action so it had to be eaten to exert its toxicity. It was apparent that ACZA was extremely toxic to the termites and very small amounts were needed to kill them although it took a long time for the termites to die. The termites apparently did not feed after the initial period. The control blocks, on the other hand, lost an average 0.84 grams or about 40.8 percent of the initial weight. This occurred in the 3 weeks that it took to complete the test. The blocks were severely damaged ( Fig. 3 ). Extensive tunneling was visible on the lower surface of the block. The termites were extremely active during the entire period of the test and no doubt would have completely destroyed the blocks in another couple of weeks. Field tests A careful examination revealed that none of the treated pieces, even those treated to a retention level of 0.1 pcf, was attacked by the termites. There were no significant differences among the treatments. Wood treated at 0.1 pcf performed as well as the wood treated at 0.6 pcf. There was no detectable damage in any of the treated wood.
That the termites were active in the traps was shown by the fact that the paper and most of the untreated side pieces were attacked and destroyed. They even built tunnels over the treated wood but did not attack it (Figure 4). There were no indications that ACZA was repellent to the termite. This is similar to the results obtained in the laboratory using the ASTM test. In the laboratory, there was no visible damage to the wood, but the mortality in the exposed termites was high. It was not known whether ACZA caused significant mortality in the field colony. ACZA is quite toxic to the Formosan subterranean termite but is slow acting. Formosan subterranean termites fed filter paper treated with ACZA at concentrations of 1.0, 0.1 and 0.01 percent, all died. The only difference was in the speed of kill. At 1.0 percent, the termites stopped feeding in two days. The workers shrunk, their movements slowed and they all died in 13 days. The soldiers were indirectly affected because the workers apparently fed them contaminated food and they died in the same period. At 0.1 percent it took 24 days and at 0.01 percent it took 27 days to reach 100 percent mortality. In the field test, the delayed action would have allowed any affected termite to leave the trap and die in some other area of the colony. Whether this occurred or not was not known because the vigor of the colony did not mean that there was no mortality.
Colonies of Formosan subterranean termites can sustain tremendous losses. As many as 500 thousand termites have been extracted from a single colony in a week with no significant reduction in activity. All of the control traps were attacked within 2 weeks after they were placed in the field. The attack generally continued throughout the entire 16 week duration of the experiment. However, the intensity of the attack diminished after 2 months because the control traps were almost completely eaten up. Termites will leave a trap after most of the wood is eaten. The termites also left some of the traps with treated wood after most of the untreated wood was consumed. There either was no attempt to feed on the treated wood or there was minimal tasting before the termites left the trap. There was some indication that the untreated 1 X 2 in the ACZA traps were not as severely attacked as those in the control traps. There were 3 untreated side pieces, one each associated with the 0.1, 0.4, and 0.6 pcf retentions, that were almost untouched. The other side was attacked. The treated pieces may have partially protected the untreated pieces by reducing the total attack on the trap. The differences among the untreated wood, however, were not statistically significantly at P = .05 (Table 4). Return to the top.
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