Drywood Termites and their importance in household and structural pest control in Sri Lanka

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November 28, 2018 6:29 am

SYNOPSIS

Drywood termites(Kiri veya) arewidespread in Sri Lanka and cause damage tomost household furniture and wooden structures. They have an organized caste system similar to bees, ants and ground-dwelling termites. They live in timber and wooden structures. Their presence in households can be determined by heaps of granules found on the floor. This is usually mistaken as attack by woodworms or wood decay. These granules may fall from the ceiling or from the furniture. Furniture made from engineered wood (example: plywood, MDF, HDF) is highly susceptible to Drywood termite attack. Gas fumigation of infested wood is the most effective treatment. However, fumigation must be performed by licensed professionals in order for the treatment to be successful. Selection of mature timber without sapwood helps prevent Drywood termite infestations. Timber seasoning, chemical impregnation and use of preservatives are other preventative methods.

INTRODUCTION

Dry wood termites are termites that live in wood or timber itself. The colonies depend on low moisture of wood and does not need external moisture source. They live in secretive manner in the deep galleries of wood and can be seen while they swarm.Colonies are relatively small in size usually have less than 1000 or some species about 2500 individuals.Compressed fecal pellets pushed out appear near the kick-out holes of infested wood are the characteristic sign of Dry wood termites .Drywood termites are belonged to the Family Kalotermitidae and the Genus Incisitermesmay be wide spread in Sri Lanka causing damage to most of the household furniture and structures.Winged termites emerging indoors are a sure sign that the building is infested. Life cycle and biology Drywood termites are eusocial insects. They live in colonies and responsibilities for reproduction, foraging caring young and defending the colony are divided among castes: reproductives (king,queen and alates), workers and soldiers. In drywood termites, the worker caste does not consist of true workers. They are not sterile, like those workers found in the higher termite Families. Young termites do the duty of worker caste, and they are known as pseudergates (false workers). All the castes have chewing mouthparts, although the mandibles of the soldiers are greatly modified for defense to the point that they must be fed by the pseudergates. All castes except the reproductives are blind.Alates emerge from exit holes in the wood and swarm in warm moist days. Then they are attracted to light. Upon reaching the outside, the swarmers disperse up to 10 to 250 feet away from the nest. Then Alates shed their wings and find partners to mate. After mating, they become king and queen and remain mates for life. The first task of the royal couple is to find a crack or crevice in a wood or wooden structure where they can start excavating a royal cell. This usually takes three to four days and when completed they seal the entrance with a plug of gut contents. Following a period of inactivity that may last up to approximately nine months, the queen begins laying eggs. Larvae hatch from the eggs and fed by the king and queen until they are large enough to feed and excavate galleries in the host wood. After two years, the colony is still quite small consisting of the king and queen, a soldier, and perhaps a dozen or so nymphs (Harvey 1934). Over time,the size ofthe queen’s ovariesincreases and the abdomen swells– a condition known as physogastry. The physogastric abdomen appears striped because the swelling stretches the abdominal intersegmental membranes so that each individual abdominal sclerite becomes visible. The king, however, does not change much in appearance, although he does shrink a bit, and looks virtually the same as when he first dropped his wings. Drywood termites obtain water either directly from the wood on which they feed or they produce it themselves through oxidative metabolism (Becker 1969). Drywood termites also have another adaptive mechanism to conserve water. Undigested matter in the gut passes through specialized rectal glands in the hindgut. These glands reabsorb water from the fecal matter producing a dry pellet with a distinctive hexagonal shape. These pellets, most of the times found in piles. This is a characteristic sign of infestation. Drywood termites expel their fecal pellets from the gallery through “kickout” holes. These holes are extremely small and usually are sealed with a plug of wet feces and pellets when not in use. They can sometimes be found by carefully searching wood surfaces directly above where fecal pellets heap up. The galleries of the Drywood termites consist of irregular excavations that extend throughout the sapwood, sometimes extend into the heartwood. Some galleries are spacious enough to accommodate large aggregations of termites while others are so narrow that termites can only pass through in single file. Another characteristic feeding behavior is that Incisitermesspecies will excavate towards the outer surface of the wood without actually breaking through it, thusleaving a paperthin, outer protective layer. Infested wood sometimes appears sound, but upon close inspection and mechanical probing this outer shell can be easily broken, revealing the underlying galleries and large amounts of frass (fecal pellets). In Sri Lanka, most of the furniture made of plywood and other engineered wood such as MDF andHDF are highly susceptible forDrywood termites. Wooden lattice of windows and air vents, wooden beading used as window glass retainers are heavily infested as they are usually made of sapwood. This infested wood can easily cross infest good timber even with heartwood.

Control

Fumigation of infested wood or structure, usually with gas fumigant, is recommended for severe or widespread infestations, or when they are in inaccessible areas. This treatment is the most effective in ensuring the whole structure is treated and all termites within are killed. On the other hand, fumigation has more limitations due to application hazards and stringent pesticide regulations.

Drilling Treatment

Mild and limited infestations which can be easily found and reached can be given a localized treatment. These “spot” treatments consist of drilling holes into the infested wood or opening kick-out holes and injecting a termiticide into the galleries. Removing and discarding infested wood can also simply done. This can be done for wood members that can be easily removed from a structure and when infestations are limited to only one or a few pieces of wood such as a door, fence post, or dead branch on a tree, etc. Freezing, localized electrocution, microwave treatment and heat treatment are also used to control Drywood termites in some countries. However, the cost effectiveness of these measures are questionable and have not been so far popular in Sri Lanka.

Prevention

Prevention of Drywood termite can be easily obtained through selection of timber for structural and other uses. Proper removal of sapwood should be thoroughly emphasized. Avoiding immature felling, proper seasoning of timber, chemical impregnation and use of other preservatives can significantly reduce the risk of infestation. Removal and destruction of infested wood members will minimize the cross infestation of fresh timber. The timber preservation methods such as Pressure impregnation are not known to many house builders, and construction professionals. Availability of the timber treatment facilities are also not sufficient in the country and therefore chances are limited for the public to prevent drywood termite infestations. Addressing these issue by government and policy makers is vital to minimize economic losses due to these pests. infested as they are usually made of sapwood. Thisinfested wood can easily cross infest good timbereven with heartwood.

Control

Fumigation of infested wood or structure, usually with gas fumigant, is recommended for severe or widespread infestations, or when they are in inaccessible areas. This treatment is the most effective in ensuring the whole structure is treated and all termites within are killed. On the other hand, fumigation has more limitations due to application hazards and stringent pesticide regulations.

Drilling Treatment

Mild and limited infestations which can be easily found and reached can be given a localized treatment. These “spot” treatments consist of drilling holes into the infested wood or opening kick-out holes and injecting a termiticide into the galleries. Removing and discarding infested wood can also simply done. This can be done for wood members that can be easily removed from a structure and when infestations are limited to only one or a few pieces of wood such as a door, fence post, or dead branch on a tree, etc. Freezing, localized electrocution, microwave treatment and heat treatment are also used to control Drywood termites in some countries. However, the cost effectiveness of these measures are questionable and have not been so far popular in Sri Lanka.

Prevention

Prevention of Drywood termite can be easily obtained through selection of timber for structural and other uses. Proper removal of sapwood should be thoroughly emphasized. Avoiding immature felling, proper seasoning of timber, chemical impregnation and use of other preservatives can significantly reduce the risk of infestation. Removal and destruction of infested wood members will minimize the cross infestation of fresh timber. The timber preservation methods such as Pressure impregnation are not known to many house builders, and construction professionals. Availability of the timber treatment facilities are also not sufficient in the country and therefore chances are limited for the public to prevent drywood termite infestations. Addressing these issue by government and policy makers is vital to minimize economic losses due to these pests.