Use of termite baits in controlling Macrotermes- a notorious agriculture pest

Introduction
 

Macrotemes gilvus belonging to the Family Termitidae is a common mound building termite species found in South East Asia, including Philippines. It’s a very important agriculture pest damaging plantation trees as well as crops like sugarcane. The height of the mound varies from few centimeters to over a meter. The species is a generalist feeder, feeding on various wood types, including barks, dried leaves and humus.  This author has also noticed difference in feeding preferences of the species, which characteristically differ between localities, presumed to be dependent on the nature and the type of food available in the area.
 

The species 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 could be observed in 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. Each of these life history characteristics are significant reason for the success of this species as well as concerns when management is to be undertaken. 
 

Macrotermes gilvus is now a common feature of suburban landscape as well as agriculture plantations in Philippines, and pose to cause trouble to pest control operators. With cities quickly growing into suburban areas, increased incident of structural infestation and defacement of wood are coming to attention. Most of the observed entry to structures are through above ground routes and moisture control has been noticed as a dominant characteristic in majority of the infested areas.   

Prevalence of Macrotermes gilvus in soil
 

To determine the prevalence of active termites in soil, author had conducted a survey using a single pest control company (Dhang, 2014). This work is 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. The stations are the largest stations available in the current industry, and has been proven to intercept all species of subterranean termites. Five hundred (500) 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 covering 28 sites in suburban Manila. The stations were monitored and the data presented accounted for the first 3 months of activity.
 

The results of the experiment is summarized in Table 1. The data show 20% of the installed In- ground baiting station intercepted termite colonies in 3 months. The major species in the soil was Macrotermes gilvus followed by Microcerotermes losbanosensis, Coptotermes gestroi and Nasutitermes luzonicus.
 

Major termite species infesting structures 

 

Controlling Macrotermes gilvus
 

It is felt that controlling M. gilvus would require a different intervention method. This 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 case to case basis only.

 

It is noticeable that most infestation and occurrence of this species in structures are above ground in nature. Consequently baiting method is most recommend when active mud trials or active infestations are located in the area of management. The use of bait against M. gilvus was first attempted by the author in 2003, the result of this work was later published (Dhang, 2011). The trial was conducted on an isolated above ground mound, categorized a medium size mound. The work documented high bait removal initially from the stations by the treated colonies. This was followed by reduced removal after 4 weeks and finally complete cessation in 10-12 weeks. The mound was dissected on week 16 and the observation were made. Dead individuals comprising of workers and nymphs in the form of shriveled up bodies were located inside the mounds. Remnants of consumed fungal combs were collected. Finally the opening of the royal chamber revealed dead queen and contaminated chamber workers. 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 use of baits in control of M. gilvus. All of these researches used a chlorfluazuron (CFZ) based processed 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 is dependent on 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 control in 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 follow a multiple path 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 CFZ is transferred from nest workers feeding on CFZ incorporated 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 CFZ to nymphs through salivary secretions. 

 

The detection of high levels of CFZ 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). CSI have been reported to be transovarially transferred to eggs, subsequently inhibiting egg development (Rojas and Morales Ramos, 2004). Eggs produced by treated reproductive may fail to hatch into nymphs thus eliminating the colony in a 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 majority of infestation follow above ground routes, which prevents use of chemical barriers. In this scenario termite baits comes to significance. With adequate evidence on efficacy, it is now easy to recommend that use of Requiem® to control M gilvus.