Development Of Entomopathogenic Nematode Use Against Termite Pests (Term Paper Sample)

DEVELOPMENT OF ENTOMOPATHOGENIC NEMATODE USE AGAINST TERMITE PESTS
TELAN, Jose Angel Jude B.
Term Paper
Submitted to Dr. Barbara L. Caoili
in Partial Fulfillment to
ENT 275: Insect Pathology
Termites are the members of the Order Isoptera which means “equal winged” and includes more than 2600 species worldwide (Engel & Krishna 2004). They are known as eusocial insects (Thorne 1997) and generally feed on wood and other plant cellulosic materials (Donovan et al. 2001). Caste system could be observed on their nests, composed of a queen which mainly functions as the egg-laying individual in the nest, workers as gatherers and foragers of food, soldiers that protect the colony, and male alates that mate and fertilize the queen (Noirot 1985, Roisin 2000). They undergo incomplete metamorphosis and are usually divided into their habitat preference or feeding habits. These are subterranean termites which utilize soil particles in their nests, drywood termites which generally build nests on dry wood, and dampwood termites which live and feed on damp wood (Eggleton & Tayasu 2001). Recent phylogenetic studies consider placing the members of this Order under the Order Blattidae, which indicates that termites are phylogenetically related to cockroaches (Inward et al. 2007). Their feeding behavior could cause economical ripples in human systems since it could be both beneficial and harmful (Bodine & Ueckert 1975).
The economic importance of termites works both ways – detrimental and beneficial. The beneficial importance of these insects is mainly attributed to their capability to break down and recycle plant matter. This allows the recycle of nutrients and release of organic matter in to the soil, maintaining soil health (Bodine & Ueckert 1975). Another benefit is that termites are one of the food sources for many organisms including ants, poultry, and mammals like humans (DeFoliart 1975, DeFoliart 1989). Out of more than 2,300 species of termites worldwide, around 180 species cause damage to buildings (Su 2003), which is detrimental to the economy. These termites are considered as pests since they damage infrastructures (Su 2003) made of wood, to forestry, and some agricultural products (Mitchell 2002). However, data are insufficient to assess their total economic impact worldwide. Different factors may affect this, including regional differences in cost of living and human attitude towards termites. But in the United States, the cost for liquid termiticide use could exceed $1.5 billion annually (Su 1994). Around 80% of these economically important termites are subterranean species. Even so, drywood termites are responsible for a significant portion of damage and control expenses related to termites not just in the United States but worldwide (Su & Scheffrahn 1990). These drywood termites could have been unknowingly transported through infested wood from place to place by ships or movement in land (Scheffrahn et al. 2009, Scheffrahn & Crowe 2011). Subterranean termites, however, could be considered as “urban pests” since they have the tendency to attack man-made structures and could be invasive causing increased structural damages worldwide (Lee 2002).
Prevention and control of subterranean termites are commonly associated with the use of liquid termiticides in treating the soil. This method is described by the injection of liquid termiticide to the soil, establishing a toxic chemical barrier against termites (Su & Scheffrahn 1998). This is commonly known as barrier treatment. The insecticides used are either neurotoxins or mitochondrial respiration inhibitors. However, this method is labor intensive and may require relatively large amounts of insecticides in the soil in order to reach the desired concentration levels for control. Also, varied successes may be attributed to differences in the soil, type and dosage of chemical, degree of infestation, and skills of the applicator. With the said factors, continuous and uniform insecticide distribution around the infested site could be difficult to achieve. Exploitation of the termites’ social character could be the main factor for the successes of the said treatments. Horizontal transfer of the active ingredients’ lethal doses after acquisition by exposed termites to other nestmates leads to their mortality (Su & Scheffrahn 1998). Aside from barrier treatments, nonrepellent delayed-action termiticides have also been used. These termiticides were considered as a “better option” due to the potential wider area coverage since the termites could transfer the active ingredients for a longer period of time since they do not die too quickly after exposure to the treatment (Su 2005). This could also allow for integrated pest management strategies that could somehow reduce the usage of insecticide doses. However, there is still potential damage in the soil and may cause possible harm on other organisms in the exposed area. Thus, baiting programs were also used. This method exploits the foraging behavior of subterranean termites by using treated wood and other cellulosic material which results to introduction of the active ingredient to the colony when feeding (Su 2002). This method requires lesser expenses and reduces the potential harm to other organisms in the infested area. However, the results are more variable since environmental and seasonal factors could come into the equation as they may affect the feeding and foraging behavior of the termites. In addition to these methods, biological alternatives were also considered like fungal, bacterial, and nematode approaches. (Verma et al. 2009)
Entomopathogenic nematodes or EPNs are one of the alternative biological control approaches aimed to insect pests. Entomopathogenic nematodes enter through orifices and cuticle with the help of the tooth possessed by Heterorhabditids (Bedding & Molyneux 1982). After exposure of the insect to EPNs, the EPNs release the bacteria that consume the insect internally while the EPN develops and proliferates inside. Once juveniles develop to their infective stage and consume the insect further, they emerge from the insect cadaver to infect other potential insect hosts, then the cycle goes on again (Kaya & Gaugler 1993). Extensive studies concerning EPN involves the families Steinernematidae and Heterorhabditidae along with their respective symbiotic bacterial genera, Xenorhabdus and Photorhabdus spp. respectively. EPNs proliferate quickly in insect cadavers, releasing numerous infective juveniles or IJs after nutrient depletion on their first host then proceed to infect other potential insect hosts (Kaya & Gaugler 1993). First entomopthogenic nematode was Aplectana kraussei as described by Steiner, which is now Steinernema kraussei (Mracek 1994). Neoplectana glaseri, now Steinernema glaseri, was discovered by Glaser, which infected Popilia japonica grubs. Field trials concerning S. glaseri were conducted during the 1930s (Glaser et al. 1930). Neoaplectana carpocapsae, now Sterinernema carpocapsae, was discovered in 1955 by Jaroslav Weiser (Grewal & Poinar 2012). Tamashiro first proposed entomopathogenic use against termites then conducted experiments concerning Coptotermes formosanus termites achieving septicemia when infected by Steinernema carpocapsae (Tamashiro 1976, Grewal & Poinar 2012). However, field trials using Steinernema sp. against C. formosanus colonies were not promising since in the field colonies, the infection was not transmitted to another host (Tamashiro 1976) despite promising laboratory trials where the nematode-infected insects achieved septicemia (Tamashiro 1976, Fujii 1976) Basic data on species with pest control potential were then published, at which allowed entomopathogenic nematodes to gain popularity for controlling various insects (Poinar 1979). Before the banning of chlordane in the United States, two products containing Steinernema sp. were marketed as “biological termiticides” and released. Even without supporting data, promotion of these products was published by means of press releases. (Chouvenc et al. 2011) Results were observed and became controversial especially with treatments against subterranean termites as success testimonies along with negative results on field tests by the USDA Forest Service researches, thereby producing inconsistent results. Steinernema feltiae were used against Reticulitermes flavipes in laboratory trials ending in success. However, when termites are established in a central nest, but nematodes were applied in a satellite container, the termite colonies were not eliminated. After 1989, no reportage of nematode use against subterranean termites appeared which could suggest the cease of their usage (Mauldin & Beal 1989, Mix 1985, Mix 1986, Hall 1986, Chouvenc et al. 2011). Application against drywood termites has also been recorded. Glyptotermes dilatatus, live-wood tea termite, was successfully controlled using Heterorhabditis sp. both in the laboratory and in the field using nematode suspension application in the wood, similar to the baiting process of eliminating termites but using live plants instead of wood (Danthanarayana & Vitarana 1987). Neotermes sp. was eliminated also in field trials from coconut palms, citrus, and mahogany trees and was discovered that inundative doses were labor intensive and termites will just escape to untreated branches. Treatment and location of all systems are problems with drywood termite especially with using localized techniques (Chouvenc et al. 2011, Lenz & Runko 1992,1995, Woodrow et al. 2006). Development on the studies occurred concerning termites, especially their characteristics that could somehow resist entomopathogenic nematode infections. Winged members of the colony, namely the alates, are somehow more susceptible to the infection as comp...