Partho Dhang, Ensystex country manager for the Philippines, examines the success of using in-ground baits against the Southeast Asian termite Macrotemes gilvus.
Macrotemes gilvus (Hagen), Family: Termitidae, is a common mound building termite species found in Southeast Asia, including the Philippines. The height of the mound varies from a few centimetres to over a metre. The species is a generalist feeder, feeding on various wood types, including barks, dried leaves and humus. The author has also noticed differences in feeding preferences, which are characteristically different between localities. This is presumed to be dependent on the nature and the type of food available in the area.
Macrotemes gilvus belongs to higher termite group, and is known to build complex fungus combs inside their mound, feeding on both the fungus heads and the growing media or the combs. However, the most intriguing feature (which often remains unexplained) is the number of mounds the species makes in a given area. Often numerous active mounds can be observed in a small patch of land. Whether this species is capable of sharing food, nest and territory among adjacent colonies is yet to be investigated in this region.
Another feature of the species commonly observed is the presence of multiple mature queens in a single chamber (Figure 1, pictured above). These behavioural and life-cycle characteristics are significant reasons for the success of this species and need to be considered when management programs are implemented.
Macrotermes gilvus is now a common feature of the suburban landscape in the Philippines and poses major challenges to pest control operators. With cities quickly growing into suburban areas, there are increased incidences of structural infestation and wood damage. Most of the observed entry points to structures are through above-ground routes, with poor moisture control the dominant characteristic in the majority of the infested properties.
Prevalence of Macrotermes gilvus in soil
To determine the prevalence of active termites in soil, the author conducted a survey using a single pest control company (Dhang, 2014). This work was to demonstrate the dominance of M. gilvus in the soil.
Exterra in-ground baiting stations provided by Ensystex Philippines Inc. were used for this purpose. These stations are the largest available in the current industry, and have been proven to intercept all species of subterranean termites. Five hundred in-ground stations containing wooden interceptors were installed and monitored for termite activity. The stations were all installed between the months of February to May 2012 and covered 28 properties in urban and suburban Manila. The stations were monitored and the data presented for the first three months of activity.
The results of the experiment are summarised in Table 1 below. The data shows 20% of the installed in-ground baiting stations intercepted termite colonies within three months. The major species in the soil were Macrotermes gilvus followed by Microcerotermes losbanosensis, Coptotermes gestroi and Nasutitermes luzonicus.
Table 1: Interception of termite species by using In-ground Bait Stations (IGS)
|Number of in-ground bait stations||No interception||Coptotermes gestroi||Microcerotermes losbanosensis||Macrotermes gilvus||Nasutitermes luzonicus|
Controlling Macrotermes gilvus
With the usual soil treatment practices having limited success in the control of M. gilvus, it was felt that a different intervention method would be required to deliver success. The author has found that physical demolition of mounds is a good method to control chances of infestation. However this method may not be foolproof and is recommended on a case-to-case basis only.
It is noticeable that most infestations and occurrences of this species in structures are above ground in nature. Consequently, termite baiting is recommended when active mud trails or active infestations are located. The use of baiting against M. gilvus was first attempted by the author in 2003 and the result of this work was later published (Dhang, 2011).
The trial was conducted on an isolated above ground mound, categorised a medium-sized mound. The work documented an initial high level of bait removal from the stations by the treated colonies. Reduced bait removal was observed from four weeks onwards and finally complete cessation in 10-12 weeks. The mound was dissected at week 16 and observations were made.
Dead individuals comprising of workers and nymphs in the form of shrivelled up bodies were located inside the mounds (Figure 2). Remnants of consumed fungal combs were collected (Figure 3). Finally the opening of the royal chamber revealed the dead queen and contaminated chamber workers (Figure 4). Each observation points to the fact that M.gilvus colonies can be negatively affected by suitable bait.
Subsequent work followed by Garcia in 2005 (Garcia et al., 2007), Peters et al. (2008) and Lee et al (2014), proved the use of baits in successful control of M. gilvus. All of these studies used the chlorfluazuron based cellulose bait manufactured by Ensystex in their work. The product is currently marketed as Requiem termite bait.
The above-mentioned studies conclusively prove the suppression and elimination of colonies of M. gilvus by Requiem. However, the success of the colony elimination program is dependent on the intensity of baiting or frequency of bait replenishment and the amount of bait going into the colony. Small to medium size colonies are easy to eliminate and can totally be eliminated within 3-6 months from the time baiting starts. Larger colonies will require more time.
The reason for the slow elimination is explained by the fact that the chlorfluazuron in the bait follows multiple paths in the complex food system of these termite species before reaching the key colony individuals.
It is proposed by Lee et al (2014) that most of the chlorfluazuron is transferred from nest workers feeding on the active incorporated in the fungus combs and fungus noodles through the salivary secretion to the developing nymphs. Foraging workers feeding on regular food as well as bait can also directly transfer the chlorfluazuron to nymphs through salivary secretions. The detection of high levels of chlorfluazuron in the workers living in the royal chamber also suggests a possibility that the compound may have been acquired by the reproductive caste (Lee et al. 2014).
Chitin synthesis inhibitors have been reported to be trans-ovarially transferred to eggs, subsequently inhibiting egg development (Rojas and Morales Ramos, 2004). Eggs produced by treated reproductives may fail to hatch into nymphs, thus eliminating the colony in the longer run.
Conclusion and recommendation
Macrotermes gilvus is an iconic species in south east Asia, simply because it is used as a specimen to study most termite management tools and systems. The species has also transformed to become an emerging pest in recent times. However, the majority of infestations follow above-ground routes, which prevents use of chemical barriers. In this scenario termite baits come to significance. With adequate evidence on efficacy, it is now easy to recommend the use of Requiem to control M.gilvus.
At this stage Requiem termite bait is the only bait that has been proven to eliminate this species of termite and this is considered a factor of both the active ingredient, and palatability to ensure sufficient active is transferred in a short period time.
Partho Dhang PhD, Country Manager, Ensystex, Philippines
Dhang, P. (2011) A Preliminary Study on Elimination of Colonies of the Mound Building Termite Macrotermes gilvus (Hagen) Using a Chlorfluazuron Termite Bait in the Philippines. Insects 2011, 2(4), 486-490; doi:10.3390/insects2040486.
Dhang, P. (2014) Examining the economics of termite baiting in a South East Asian scenario. Proceedings of the Eighth International Conference on Urban Pests Gabi Müller, Reiner Pospischil and William H Robinson (editors) 2014 Printed by OOK-Press Kft., H-8200 Veszprém, Papái ut 37/a, Hungary, pp 279-283.
Garcia, C.M., Giron, M.Y. and Broadbent, S.G. (2007) Termite baiting system: a new dimension of termite control in the Philippines. Proceedings of the 38th International Research Group on Wood Preservation, Wyoming, USA, May pp 12.
Peters, B.C., Broadbent, S.G. and Dhang, P. (2008) Evaluating a baiting system for management of termites in landscape and orchard trees in Australia, Hong Kong, Malaysia and Philippines. In: Robinson W.H. and Bajomi D. (eds.) Proceedings of the Sixth International Conference on Urban Pests, Budapest, July 2008, OOK-Press, Budapest pp. 379-383.
Rojas, M.G. and Morales-Ramos, J. A. (2004) Disruption of reproductive activity of Coptotermes formosanus (Isoptera: Rhinotermitidae) primary reproductives by three chitin inhibitors. Journal of Economic Entomology 97, 2015-2020.