Evaluation of Lahar Barrier to Protect Wood Structures from Philippine Subterranean Termites

Transcription

1 142 (1): 21-25, June 2013 ISSN Date Received:?? Feb 20?? Short Note Evaluation of Lahar Barrier to Protect Wood Structures from Philippine Subterranean Termites Menandro N. Acda Department of Forest Products and Paper Science College of Forestry and Natural Resources, University of the Philippines Los Banos College, Laguna, Philippines Volcanic debris consisting of a sandy aggregate (lahar) from Mt. Pinatubo Central Luzon, Philippines was used as physical barrier to prevent tunneling and penetration of Philippine subterranean termites into a small wooden structure. The protective barrier consisting of mixed lahar particles was installed beneath floor and concrete foundation walls. Regular inspections were made over a five year period to determine signs of termite damage inside and outside of the structure. Results showed that Philippine subterranean termites were unable to penetrate the 5.0 cm thick layer of 1.18 to 2.40 mm lahar particles from the underground soil. The structure remained in good condition with no sign of termite damage to the wooden interior. The study indicated that lahar barrier could be used to protect wooden structures from entry of subterranean termites and offer a non-chemical alternative to commercially available termiticides. Key Words: lahar, physical barrier, non-chemical method, Mt. Pinatubo, termites INTRODUCTION The Philippines is located in a region where subterranean termites are widely distributed and causes substantial damage to homes and wooden structures (Yudin 2002; Acda 2007). Four species of subterranean termites, viz, Coptotermes gestroi Wasmann (formerly known as Coptotermes vastator Light), Nasutitermes luzonicus Oshima, Macrotermes gilvus Hagen, and Microcerotermes losbanosensis Oshima are of economic importance and considered serious structural pest in the Philippines (Acda 2004). These species attack wood buried in or in direct contact with the ground and their activities result in early replacement and reduction of service life of wooden structures. Termite control methods such chemical barrier, baiting and dusting are available in the Philippines. Both repellent and non-repellent termiticides are currently being used for termite control. However, cost of treatment and *Corresponding author: mnacda@yahoo.com health risk prevented homeowners from availingtermite control services in the Philippines (Acda 2013). These factors prompted research on alternative control methods that are affordable and safe for both man and environment. Non-chemical termite control methods such as biological control using pathogenic fungi and nematodes, and physical barriers using stainless steel mesh and crushed rockshave been reported in the literature but not used in the Philippines (Chouvenc et al. 2011). Volcanic debris, consisting of sandy aggregate called lahar, had been reported to be an effective barrier in preventing tunneling and penetration of subterranean termites in laboratory and field trials (Acda & Ong 2005a, 2005b). Similar barrier consisting of crushed rocks, glass, sand, etc. have been reported in the literature (Su et al. 1991; Su & Scheffrahn 1992; Myles 1997; French et al. 2003). However, the natural sharp edges of lahar particles due to its volcanic origin results in penetration distance significantly less than that reported for other aggregates used as barrier in the literature (Acda 2005b). 21

2 The use of lahar barrier may be an attractive alternative in countries where volcanic eruption resulted in the deposition of huge quantities of ash and volcanic materials in the surrounding environment. The eruption of Mt. Pinatubo in 1991 in the Philippines ejected about 11 billion cubic meters of ash and volcanic debris covering about 400 square kilometers of land (Newhall and Punongbayan 1996). Despite continuous quarrying of lahar aggregate for civil and construction works, billions of tons of lahar still block rivers and waterways in the southern provinces of Luzon. The present paper reports on the use of mixed sized particles of lahar as protective barrier to prevent entry of subterranean termites into a wooden structure. MATERIALS AND METHODS A layer of lahar barrier (5.0 cm thick) consisting of screened particles obtained from Sto. Tomas River, Pampanga province ranging in size from 1.18 to 2.40 mm was installed beneath the floor and foundation walls of a model house (5 meter wide x 5 meter length x 6 meter high) (Figure 1). The effective particle size and barrier thickness was based on a previous laboratory and field studies (Acda and Ong 2005a, 2005b). The lahar particles were uniformly laid out and tampered prior to the pouring of concrete. Before concrete was poured, a small PVC pipe (25 mm diameter by 4.0 cm long) filled with lahar particles were planted vertically on top of the lahar barrier following a grid pattern (60 cm apart) that extended the whole floor area of the house (Figures 2 and 4). The PVC pipe served as entry point for termites if they breach the barrier. It also simulates cracks and openings that develop on concrete slab construction with time. The house was supported by wooden columns sitting on a concrete base which was surrounded by lahar particles on all sides. Hardwoods purchased from a local hardware were used for framing and side paneling. Windows with glass panes and flushed wood door were installed on site. Interior type plywood and galvanized iron sheets were used for ceiling and roof, respectively. Several non-durable logs (15 cm in diameter by 1 m long) were placed inside the house to serve as termite baits (Figure 3). The house was built in the University of the Philippine Los Banos campus where active colonies of Coptotermes, Macrotermes, Nasutitermes, and Microcerotermes are present. The surrounding was cleaned regularly and kept free of fallen leaves. Monthly inspections of the inside and outside of the structure were made to determine the ability of the barrier to prevent penetration of subterranean termites. The house was uninhabited and only limited movement inside was allowed to facilitate cleaning during inspection. Evaluation was started in 2008 and completed in Figure 1. Model house used to test ability of lahar barrier to prevent entry of Philippine subterranean termites. 22

3 Figure 2. Lahar barrier being installed prior to pouring of concrete; short PVC tube filled with lahar particles were used to provide termites with entry points to the house if the barrier is breached. Figure 3. Non-durable logs placed inside the house to serve as termite baits. RESULTS AND DISCUSSION Regular inspection during the five year evaluation period showed no signs of termite activity inside the structure. All paneling and wooden members showed no signs of termite activities or damage caused by the insects. Log baits placed inside the structure also remained intact with no sign of termite damage. Apparently, the lahar barrier prevented penetration of subterranean termites from the underground soil. Tree branches that regularly fall near the structure were readily devoured by M. gilvus. Mound of M. gilvus and nest of M. losbanosensis were located two 23

4 Figure 4. PVC tubes extending to the level of the lahar barrier to simulate cracks and openings that developed with sub-slab construction. and four meters from the house respectively. Buildings about 5-10 meters away from the structure were regularly penetrated by N. luzonicus, M. losbanosensis, and C. gestroi. These buildings were treated twice with liquid termiticides in the last five years to minimize termite infestation. However, subterranean termites regularly breached these structures mainly from cracks on the walls and floors of the buildings. These observations indicated a high termite pressure in the area. After 14 months in the evaluation period, M. losbanosensis tried to gain entry to the house by building mudtube on the exterior concrete wall located on the south side of the house. Further investigation revealed that the termite reached the wall by building tubes on top of the lahar aggregate surrounding the structure. Apparently, M. losbanosensis were unable to breach the house from underground forcing it to build mudtubes in the open. The termite successfully built tube across the barrier and about four cm high on the wall before being discovered. Brushing the tubes on the ground and off the wall stopped the M. losbanosensis from advancing further up the wall. However, M. losbanosensis returned after two months of its initial attempt and again constructed tubes on the surface but failed to reach the outer wall. The M. losbanosensis mudtubes were never observed again near the house after that incident. M.gilvus also built wide mudtubes near and on the surface of the lahar particle barrier on the north and east sides of the house during the 23rd month of evaluation. The foraging activities of M. gilvus were very close to the base of the concrete wall. However, the termites did not attempt to climb the wall and seemed interested only in foraging for decaying leaves on the surface. These species are known to limit their activities on the ground and seldom climb structures to reach wood above ground. A simple breaking of the tubes stopped M. gilvus from further attempt to forage near the house. Similar incidents were observed in the subsequent months and were controlled as described above. The absence of human activities in the house probably encouraged the termites to forage around the structure. No sign of penetration was observed from Coptotermes species, although it was discovered later on that an Araucaria tree 10 meters away from the house was infested with C. gestroi. At the end of the evaluation period, the house remained free of termites and no sign of termite activities were observed inside the structure. SUMMARY AND CONCLUSIONS Lahar barrier consisting of mixed particle size from 1.18 to 2.40 mm was installed uniformly (5.0 cm thick) beneath floor and foundation walls of a small wooden house to 24

5 determine its ability to prevent termite penetration. The house was constructed using wooden frames, panel boards and plywood. The floor and foundation walls were made of poured concrete. Active termitecolonies of Coptotermes, Macrotermes, Nasutitermes, and Microcerotermeswere known to be active on the ground or buildings near the structure. Regular inspections were made over a period of five years to determine signs of termites or termite activities inside and outside of the structure. At the end of evaluation period, the treated house was in good condition with no sign of termite damage to the wooden interior. The log baits placed inside the structure showed no sign of termite damage and all simulated cracks on the floor showed no sign of breach or termite penetration. Termite foraging activities, however, were observed at or near the concrete exterior wall of the structure. Several times during the evaluation period, termites attempted to build tubes on the ground to reach the wall. However, their activities were discovered and tubes destroyed. Apparently, subterranean termites were unable to breach the barrier from underground forcing them to build mudtubes in the open in an attempt to reach the structure. Once in the open, termites were easily discovered and control measures become simple and straightforward. In summary, this study showed that lahar barrier could be used to protect wooden structures from entry of Philippine subterranean termites and offer a safe alternative to chemical termiticides. However, the results of the evaluation should be taken with caution due to the limited replication used in this study. Further work is needed to validate this observation commercial application. ACKNOWLEDMENTS The author thank the Charles Lindbergh Foundation, Anoka, Minnesota, USA and the Ford Conservation and Environmental Grants for financial support for this project. ACDA MN, ONG HB. 2005a. Use of volcanic debris as physical barrier to prevent tunneling of the Philippine milk termite (Isoptera: Rhinotermitidae). Sociobiology 46 (1): ACDA MN, ONG HB. 2005b. Penetration of lahar aggregates by Philippine subterranean termites (Isoptera: Termitidae). Sociobiology 47 (1) CHOVENC T, SU NY, Grace JK Fifty years of attempted biological control of termites Analysis of a failure. Biological Control 59 (2): FRENCH JR, AHMED B, TRAJSTMAN A Laboratory and field evaluation of granite aggregate as a physical barrier against subterranean termites of the genus Coptotermes spp. (Isoptera: Rhinotermitidae). Sociobiology 42 (1): MYLES MG Comparison of the penetrability of smooth and crushed sand by subterranean termites (Isoptera: Rhinotermitidae). Sociobiology 30 (3): NEWHALLL CG, PUNONGBAYAN RS (Eds.) Fire and Mud: Eruptions and lahars of Mount Pinatubo, Philippines. Seattle: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Quezon City and University of Washington Press. 1126p. SU NY, SCHEFFRAHN RH Penetration of sizedparticle barriers by field populations of subterranean termites (Isoptera: Rhinotermitidae) Journal of Economic Entomology 6: SU NY, SCHEFFRAHN RH, BAN P Uniform size particle barriers: a physical exclusion device against subterranean termites (Isoptera: Rhinotermitidae). Journal of Economic Entomology. 83 (3): YUDIN L Termites of Mariana Islands and Philippines: damage and control. Sociobiology. 40 (1): REFERENCES ACDA MN Economically important termites (Isoptera) of the Philippines and their control. Sociobiology 43 (2): ACDA MN Handbook on Philippine Termites. University of the Philippines Los Baños Publications Office, College, Laguna: 125. p. ACDA MN Geographical distribution of subterranean termites in economically important regions of Luzon, Philippines. The Philippines Agricultural Scientist (in press). 25