CHAPTER
9
Order. Isoptera
Termites
Termites are
true social insects. They not only live in colonies, but divide labor so that
different forms or castes carry out prescribed duties for the good of the
entire colony. No individual termite can survive alone. These insects can be considered beneficial or
harmful depending upon one’s frame of reference. Worldwide, they are extremely beneficial as
decomposers of dead trees, leaves and other sources of cellulose. On the other
hand they are major pests on agricultural crops, forest nursery seedlings, rangeland
grasses, stored products, and household furniture, not to mention their extreme
importance as structural pests worldwide.
Biology. From an evolutionary standpoint, these
insects are considered somewhat primitive, but their social organization is the
best developed of the insects. Along with
ants and the more highly organized bees and wasps they belong to the truly
eusocail insects. The common traits of
eusocial insects include the following: 1. Cooperative caring for the young. 2. A
division of labor with different forms carrying out different functions for the
overall good of the colony. 3. An overlap of at least two generations so
that at some point the offspring can assist their parents in colony development.
By
necessity, in order to develop colonies, social insects must be long-lived. One of the limiting factors to accomplish
longevity is a continuous source of food.
Of course termites feed on one of the two most common sources of food in
the world, namely plants (as opposed to animals) or, more specifically,
cellulose.
The two
major families of termites in the
Caste
System
As
previously indicated termites are true social insects and have a very advanced
social system with different forms (castes) carrying out different
functions. The castes in a mature
termite colony are discussed below.
Reproductives-Queen/King. The sole function of the queen is to lay
eggs. She is quite long-lived and, in some African species, the queen may lay
up to 10,000 eggs a day for 30 years.
She basically is a big egg laying machine with a huge abdomen and
engorged ovaries. The queen termite is
so large and heavy bodied that she is incapable of moving on her own. If there
is a need to change her location, the workers will line up on one side of her
and roll her like a pencil. As the eggs
exude from her abdomen they are carried away by worker termites that also
continuously feed her. Of course there is a king which is diminutive when
compared to the queen. How he mates must
be private as there is little in the literature about him. It must be difficult.
A
queen of an African termite is capable of laying 10,000 eggs a day for 30 years.
Supplementary or
substitute reproductives. There are
usually two types of this caste which are also known as neotenics. These may be either lightly pigmented with
short wing pads (brachypterous) or very lightly pigmented with no wingpads. These, as their names imply, can lay eggs
under certain conditions, depending on species.
Replacement reproductives of subterranean termites. Image courtesy of Jim
Kalisch, Dept. Entomology,
Soldier Termites. Soldier termites are easily recognized
by their relatively large heads and protruding mandibles. The soldier’s
function is to protect the colony, mainly against their chief enemies the ants.
In the mound building termites of Africa,
Left. A soldier subterranean termite with disproportionately large head.
Right. A nasute worker.
Image
courtesy Whitney Cranshaw, Colorado State Univ., Bugwood.
Worker Caste. The worker caste comprises the
overwhelming majority of termites in a colony. As their name implies, they
perform all the work in a given colony, including foraging for food (cellulose)
which is digested and in turn is regurgitated (stomodeal feeding) and or
excreted (proctodeal feeding) to fed the young, soldiers and king and queen of
the colony, excavating their tunnels or galleries, and ministering the queen.
An army of subterranean
termite workers.
Alates. In the spring and or fall, depending on
the species, a mature termite colony may form a large number of alate (winged)
termites. These are the potential kings and queens of a new colony. Very
frequently following the first seasonal rain, these alates will swarm, or fly,
from the colony. The significance of swarming following the first rain of the
season is several-fold. Termites are soft-bodied and susceptible to
desiccation; therefore, moisture is conducive to survival. It is important also
that most of the colonies in an area swarm at the same time. This insures that
mates will be found and, more importantly, there will be cross mating between
colonies to prevent inbreeding. Finally, the rain softens the soil (in the case
of subterranean termites) and enhances the chances of some species forming new
colonies below ground.
Swarming
subterranean alate termites—these potentially will become the kings and queens
of new termite
colonies. Image
compliments of Charles Hogue. L.A. County Natural History Museum.
Hundreds of
alates will leave a mature colony during swarming. They are weak fliers and
many are lost to birds, ants and other predators. Because they are weak fliers,
they do not fly great distances before settling down. Once a female alate
leaves, she releases a sex pheromone from her abdomen that attracts an alate
male. After mating, they both break off their wings that are no longer needed
and burrow into the ground or into a wooden structure to start a new colony.
Then they form a small cavity within which the female will lay several eggs. For
the first year the king and queen do not eat, but dissolve their wing muscles
to produce nutrients that they feed to the nymphs. Once these nymphs develop
within the first year, they take on work duties. Colony growth is slow and
there are no signs of this new colony in or around a structure for the first
two to three years after initial infestation.
The alates
are the most likely caste someone is likely to see. Therefore, it is to the advantage of the
professional pest control operator to be able to distinguish and teach the
differences in appearance of these from carpenter ants, similarly appearing
insects that can also swarm. Even though
they may seem similar, there are very distinct differences in the morphology of
the two.
The order of
termites is Isoptera. Iso in Latin means
equal and of course ptera refers to wings.
In winged termites the first and second pair of wings is of equal size
and shape while in winged ants the second pair of wing is much smaller than the
first. Also with termites there are many
more veins in the wings and when at rest the wings are held flat over the back
while ant wings project out from the body.
In addition the wings of termites are very large and extend way past the
tip of the abdomen while ant wings do not.
In addition ants have elbowed antennae and termites have bead-like
antennae. Finally, in ants the thorax is
joined to the abdomen by a stalk or petiole, while that of termites is broadly
joined. I am sure that is more than you
ever wanted to know about the morphology or structure of these two groups of
insects.
A
carpenter (left) ant with elbowed antennae, petiole, and unequal wings. An
alate termite (right) with beaded antennae, broad waste and equal sized wings
that lay flat over the back. Image
courtesy of Jim Kalisch. University of Nebraska Entomology.
DRYWOOD
TERMITES
Drywood
termites (Family-Kalotermitidae) establish their colonies in non-decayed wood
with relatively little moisture content (generally 2.8 to 3% water
content). Unlike subterranean termite
they never require contact with the ground.
There are 16 species of Kalotermitidae in the US. The most important in the West of are Cryptotermes brevis-the powderpost
termite, Marginitermes hubarderi-the
desert drywood termite and Incistermes
minor-the western drywood termite.
Western
Drywood termite. The western
drywood termite is by far the most common and damaging of the three above
mentioned species in California. It
extends as far north as the Sacramento Valley and eastward to the fringes of
the Arizona desert. It is occasionally
accidentally transported to colder regions as colonies can be quite small and
can withstand very low moisture. As a
result movement occurs in furniture, books, crates and the like.
The eggs of
this species hatch in 30 to 60 days depending on temperature. There are a total of 7 nymphal instars. With drywood termites there is no worker
caste and the nymphs carry out the work duties.
The first three nymphal instars of drywood termites remain
undetermined. Once the 4th
through the 7th instars are reached, they can eventually become either
replacement reproductives, or soldiers, depending on colony need. Alates can only develop from an eighth
instar nymph.
Schematic
presentation of caste formation in drywood termites.
The drywood
termite can be identified in the alate form by its reddish head and thorax and
light black wings. Mature colonies of drywood termites are relatively small and
rarely number more than 5,000 individuals. They almost always are found above
ground, located inside wooden sections of the house, more typically in attics
and upper areas. Colonies of this species develop quite slowly. A one-year old infestation typically contains
6 to 40 nymphs, one soldier and of course the king and queen. Three, four and
15-year old colonies will typically have 40 to 165 individuals with 3 soldiers,
70 to 700 individuals with 6 soldiers, and 2350 to 2750 individuals with 10 to
14 soldiers, respectively. Alates typically are only produced after the fourth
year. It is believed that the primary queen reaches her maximum egg laying capacity
at about 10 to 12 years. After that
point she declines quite rapidly and secondary or replacement queens will soon
take over.
As
previously indicated, colonies of drywood termites tend to be relatively small
when compared to those of subterranean termites. Correspondingly, less rapid and sever damage
may result from a colony of this type of termites when compared to those of
subterranean termites. However,
proliferation of colonies in a structure can result in severe damage.
A colony of drywood termites including
the red alates with dark wings.
Image
compliments of Department of Entomology, University of California at Riverside.
There are a
number of signs or symptoms of the presence of drywood termites. Of course the homeowner is the likely
individual to actually see the swarming alates.
Swarming of this species typically occurs in the fall months (September,
October), more often than not on a sunny day with temperature around 80 F. Of course it is not uncommon for a number of
these weak fliers to be caught in spider webs which can be a useful sign of an
infestation.
The common
indication of the presence of this termite is piled or scattered brown fecal
pellets below infested wood. Typically
there is little evidence of their presence on the outside of the infested
wood. The pellets are kicked out of the
termite galleries through small “kick holes” (about the size of a BB) to the
outside. The pellets typically are rectangular in shape with rounded ends and
six flattened or depressed surfaces.
Longitudinal ridges occur at the angle between the six surfaces.
In addition
there frequently are many termite wings in an infested area. Of course these are due to the previous
presence of alates which broke off their wings soon after mating. Finally it is quite easy to tell the type of
termite that has been present by the galleries of tunnels wood itself. Drywood termites feeding galleries tend to
cross the annual growth ring of wood while subterranean termites do not.
Cross section of a 2 X 4 with western
drywood termite galleries crossing the annual growth rings. In addition galleries are clean, free of
soil.
Powder-post
termites-Cryptotermes brevis. This species is well established in
Hawaii, Florida and Louisiana. Like
other species of drywood termites they can infest wood with very low moisture
content and require no contact with the ground.
Powder-post termites can infest homes but are best know for their
infestations in furniture and other small wooden products. Although the pest control operator is not
likely to encounter these, it is worthwhile to be aware of their existence as
occasionally they are imported from tropical countries in wooden objects.
Desert
drywood termite-Marginitermes hubbardi. This termite replaces the western drywood
termite in the more arid desert regions of southeastern California, Arizona and
northern Mexico. The alates are yellow
to brown and about the same size as their more common counterpart. The alates emerge at night, usually just
after a rain and are attracted to lights in huge numbers.
Drywood
Termite Control.
There are
several techniques that are used to treat infestations of the western drywood
termite. These can be broadly categorized as whole structure treatment and
local treatment.
The
advantage of whole structure treatment is that this greatly increases the
chances of total elimination of drywood
termites
from a structure. If properly applied
fumigation and heat treatment will typically result in 100% control of drywoods
and any other insect pests in the structure as far as that is concerned. Of course both of these treatments are
considerably more expensive than any of the local
treatments. Also neither of these gives any residual
control.
Local treatments, as previously indicated,
are less expensive than whole structure treatment and can vary considerable in
effectiveness. The main limitation of
these types of
treatment is that even with
great inspection techniques it is quite possible that deep seated infestations
can not be found and therefore not treated.
Also with the exception of
spot treatment with
chemicals none of these give any residual control.
Microwaves. In the below case three microwave
generators (one foot apart) are mounted against wall on a pole. As with the common microwaves that are found
in almost every home these machines produce a penetrating heat which in this
case is lethal to termites (basically the waves cook the termites inside the
wood). These machines typically are used
for local infestations with each treatment limited to small areas. As a result the poles and microwave machines
are moved to the next area after each treatment.
A
disadvantage as with all types of localized treatment detection is critical to
success and in some situations it is very difficult to locate deep seated
infestations. In addition microwave treatment may damage certain types of
surfaces and other materials, especially with high voltage machines. The main
advantage when compared to localized chemical control of course is that there
is no chemical residue.
Microwave
generators used for drywood termite control.
Image courtesy
University
of Toronto, Urban Entomology Program.
Electricity. High voltage electricity, or electrocution, is an additional
nonchemical option for controlling drywood termites. In this case infested damaged wood is exposed. Then an Electro-Gun is
placed on one side and ground on the other side of the infested timber. Electrical shock of low current (~0.5 amps),
high voltage (90,000 volts), and high frequency (60,000 cycles) jumps into
termite galleries and ends at the ground. Death results from by electric shock, although
delayed mortality may also occur from the destruction of intestinal protozoa.
Besides
the limitations of all localized treatments the efficiency of this type of
treatment may be reduced by interference of a number of standard building
materials such as glass, concrete and metal.
In addition if drill holes are required to reach infested wood damage
may occur to wall coverings and structural wood.
Electricity
generating machine used for drywood termite control. Image courtesy of University of Toronto, Urban
Entomology Program.
Freezing. Liquid nitrogen is pumped
into the infected area chilling it down to -20 degrees (F) freezing the
termites. This is not practical for
treatment of large areas, or by window glass (can shatter glass): Tarps are
used for larger areas like porches. Liquid
nitrogen has no residual activity when used alone. Minor damage to the
structure occurs from the holes drilled for spot liquid nitrogen insertion.
Liquid
nitrogen application for drywood termite control. Image courtesy of University
of Toronto, Urban Entomology Program.
Drill and Treat with Chemicals. Wood
injection or "drill-and-treat" applications have been used since the
1920s to treat drywood termite infestations which are accessible and
detectable. An insecticide is injected into small holes drilled through any
wood surface into termite galleries delivering the treatment directly to the
pest population. This is the simplest and most direct method of treatment. The
amount of drilling required and the effectiveness of this treatment depends on
the chemical used and the nature of the infestation. Most chemicals will remain
active in the wood after treatment to thwart resurgent colonies.
The chemical options include aerosol
pyrethrum and aerosol and liquid pyrethroids (cyfluthrin, permethrin,
bifenthrin), liquid imidacloprid, liquid nitrogen, and liquid and dust
formulations of disodium octaborate tetrahydrate. Chemicals that have been
phased out of commercial use include organophosphates, carbamates, silica-gel,
and dri-die.
Heat Treatment. Heat treatment is a source of partial or
complete building control for drywood termites.
In the case of complete control nylon tarps are used to tent the
building. Normally materials that are not heat resistant are removed from the
building and water is left running to protect plastic pipes. With
this technique propane heating units blow hot air in and around to heat the
structure to120 F for 35 minutes to 130 F for 1 hour.
Whole structure heat treatment is
attractive to certain homeowners who object to the use of chemicals. In
addition the process can be accomplished in a short period of time (hours)
instead of days with fumigation. Parts
of structures (e.g.-apartments and condominiums) can be treated as opposed to
fumigation where this cannot be accomplished. The major drawbacks of heat
treatments include the difficulty in raising the internal core temperature of
large structural beams that are infested and heat sinks, which are areas within
the structure that are difficult to heat, such as wood on concrete or tile. In
addition materials such as plastics (e.g. electrical outlet covers), cable
wiring and other sensitive material may be harmed by high temperatures.
Heat
treating home for drywood termites.
Image courtesy of University of Toronto, Urban Entomology Program.
Tent Fumigation. Sulfuryl floride (Vikane) is the highly
toxic, colorless, odorless gas that is used for fumigation. Since it is odorless low percentage of
chloropicrin (tear gas) is added to the main fumigant as a marker or indicator
of the presence of the gas. Fumigation (tent fumigation) with this
material is highly effective if properly applied. An important aspect which
increases the chances of successful fumigation is monitoring the distribution
of the gas within the treated structure. This is accomplished by installing gas
monitoring lines inside the structure undergoing treatment. Nonmonitored
fumigation may not have enough gas concentration to kill infestations and
failures may occur.
Generally,
human deaths occur in California every year as a result of this practice.
Vandals, thieves, and the homeless are the most common victims. A tented home
with nobody home is a prime target for burglars. This procedure presents
virtually no threat to the homeowner because Vikane has a very short residual
and is gone within a short amount of time. Tear gas (choloropicrin) is mixed
with Vikane as a warning agent and it will quickly alert the homeowner if any
residual gas remains. Tear gas has a
slightly longer residual activity than Vikane.
Home under tent fumigation. Image courtesy of Lloyd Pest Control.
Fumigation's advantage over localized treatment is
that it may eliminate infestations that are hidden from view. Major issues to
consider with the use of fumigants include the difficulty of installing
tarpaulins, the difficulty in determining the proper dosage, the need to
protectively bag food items, and the lack of residual control. In addition the
structure must be vacated for 2 to 3 days while it is being treated and then
ventilated. Additionally, some types of roofs may be damaged by having
tarpaulins dragged across them.
Of course
there is always the reluctance of certain individuals to use pesticides in
general. It should be noted even though sulfuryl floride is a highly toxic
pesticide that after the required three day treatment and ventilation period
there is essentially no toxic residue of the chemical left.
The following
(Table 1) is a summary of the advantages and disadvantage of the commonly
used
techniques used for control of drywood termites. The table is courtesy of UC IPM.
Termite Inspections
Anytime a house or other structure is sold and is
financed by conventional means such as FHA, VA or banks, a termite inspection
is required by the lending institution. The lender needs to be sure the
structure is not totally riddled with these pests, as it legally owns the house
until the loan is paid off (which in many cases take as long as 40 years). If a
home is inspected and termites are found, they must be controlled before the
loan is granted. Any termite damage or violations of the structural building
code that may lead to termite infestation must also be corrected. In some cases
the total cost of this work can be in the tens of thousands of dollars.
In rare cases, real estate agents have advised termite
inspectors to ignore existing termite problems to prevent complicating or ruining
a sale, as the seller must pay to correct existing problems. In California and
other states, there are boards that regulate pest control operators. If
homeowners believe that they have not been treated correctly by a pest control
operator, they can contact the board that will investigate the situation. If
there is something wrong, the pest control operator must correct the situation
at no cost to the homeowner.
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Subterranean Termites
Western
Subterranean Termite-Reticukitermes
hseperus. This is the
principle subterranean termite in the western US ranging from British Columbia
to Western Mexico and California to eastern Idaho and Nevada. The alates are distinguished from other
common species by their black to dark brownish coloration. Swarming typically occurs in later-winter or
spring although timing can vary considerable depending on area and
weather. As the name implies, colonies
of these insects typically are found below ground. In some cases the colonies
may extend as much as 30 feet below the soil surface. Mature colonies tend to
be very large and can contain as many as 300,000 individuals. Soil moisture is
a critical factor in the environment of these insects. Subterranean termites
typically are more of a problem in clay, as opposed to sandy soil, because clay
has the capacity to hold moisture over a longer period of time than does sand.
A
black subterranean termite alate.
As with most
termite colonies growth is slow. Only a
few eggs are deposited the first year and require an average of 50 days to
hatch. Even under the best of conditions
alates do not appear in a colony until the 3rd or 4th
year. Later the supplementary
reproductive become quite prevalent and greatly accentuate growth of the
colony. However, since colony growth is
slow signs of a new infestation in a building will take 3 to 4 years.
Unlike
drywood termites subterranean termite colonies typically require ground
contact. Apparently if there is
sufficient food, water and warmth colonies can survive above ground but this is
rare. In most areas the ground serves as
a protective barrier against extreme temperatures and as a reservoir of
moisture. Unlike drywood termites
subterranean termites are quite susceptible to dry conditions. Colonies of subterranean termites will
readily change the depth in order to seek favorable temperature and moisture
conditions.
Signs
of an Infestation. In the US if subterranean termites are found below a
structure, they can gain access to the house by building earthen tubes (shelter
tuber) or by working their way through inter-veining wood. They feed in the
wood of the house but will also return periodically to the colony via the
earthen tubes to replenish the moisture content of their bodies. If a house is
built on a slab-type foundation, these termites can gain access to the home via
cracks or holes in the slab for sewer inlets and gas fixtures. The shelter tubes also serve to protect these
termites from predators, namely ants.
These shelter tubes are constructed out of sand or dirt, bits of wood
and even fecal pellets. These are bonded
by a glue-like material that is secreted by the worker termites.
The western
subterranean termite uses at least three types of shelter tubes. Utility tubes are used to gain access to the
house and run from the soil to the first wooden member of the structure and of
course return to the soil to replenish the termites lost body moisture. These tubes are typically flattened, wide and
extend from the soil to the wooden construction above. Exploratory or migratory tubes are similar to
utility tubes but typically do not extend to the wooden parts of the structure,
are less study and have small exit holes.
As their name implies they are used to seek out new locations of
food. Suspend or drop tubes extend down
from the wooden structure and may or may not reach the ground depending on
their stages of construction. They are
normally lighter in color than the other types of shelter tubes since more wood
fiber is used in their construction since they are used by stranded termites in
attempt to return to the soil.
From Left ot Right Utility, Exploratory and
Drop Tubes.
Besides the
earthen tubes additional signs of an infestation of subterranean termite
infestation in a structure include the alates, wings that have broken off the
swarming alates and the presence of dark areas in wood and blistering of the
floor. Sometimes the distinct sound of soldiers can be heard by knocking or
tapping infested wood. When disturbed
this caste will violently jerk its head against the roof of the gallery and
make a distinct almost ticking sound.
This is though to serve as an alarm of possible danger to other
soldiers.
Subterranean
termites feed primarily on soft spring growth.
As a result the tunnels of galleries of these insect have more of a
layered appearance as opposed to the random indiscriminant burrowing
across and with the grain of infested wood by the drywood termites. In addition these termites tend to bring
small amounts of soil into their galleries and even pack chewed wood and other
sources of cellulose into the unused portions of their galleries. Because
colonies of these insects are so much larger than those of drywood termites,
damage can be far more rapid with subterranean termites than with drywoods.
Wood
with subterranean termite gallery with layered tunnels limited to soft spring
growth and packed with chewed food.
Image courtesy of University of Nebraska Entomology-Jim Kalisch.
Subterranean
Termite Control
Soil
Barrier Termiticides. Soil treatments rely on creating a toxic
chemical barrier in the soil between a potential nest and wooden parts of the
structure. Many of the older chemicals have repellent characteristics and
termites avoid treated soil. To achieve termite control for long periods of
time, such termiticides must be applied as a continuous barrier in the soil
next to and under the foundation. If there are untreated gaps in the soil,
termites may circumvent the chemical treatment. Hence, such treatments during
preconstruction can provide for more uniform coverage. Once a home is
constructed, the chemical has to be injected through drill holes and trenching
around the foundation, which can result in less accurate coverage. Termiticides
that act by creating a chemical barrier in the soil include bifenthrin
(Talstar®), cypermethrin (Demon®, Prevail®), and permethrin (Dragnet®,
Prelude®). Chlorpyrifos (Dursban®) can be used only during preconstruction and
only until December 31, 2005.
Spot treatment refers using barrier termiticides only
in those areas of the structure where termites have been detected. Many pest
management firms avoid or will not guarantee such treatments since termites are
capable of finding other untreated points of entry into the structure.
Localized spot treatments are considered risky except in re-treatment
situations.
Some of the newer
termiticides are marketed as non-repellent to termites with delayed toxicity.
As termites penetrate the "treated zone," they contact the active
ingredient, possessing delayed mortality. Since the termites are not
immediately killed, the toxicant is thought to be passed to nest mates through
grooming activities and social food exchange (trophallaxis). With this type of
activity control usually is achieved within three months. Non-repellent
termiticides include fipronil (Termidor®), imidacloprid (Premise®), and
chlorfenapyr (Phantom®).
Baits.
Termite baits rely on wood or a cellulose
matrix that is attractive to termites and are impregnated with a slow-acting
pesticide. The theory is that termite workers will feed upon the bait and
transfer it by trophallaxis to other colony members, eventually reducing or
eliminating the entire colony. Another advantage of using slow acting active
ingredients is that termites tend to avoid sites where sick and dead termites
accumulate.
Typically, in-ground stations are inserted in the soil
next to the structure and near known or suspected sites of termite activity.
These stations often initially contain untreated wood or other attractive
materials that serve as a monitoring device. The monitoring wood is replaced
with the toxicant once termites have been detected feeding on it. In addition,
above ground stations may be installed inside or on the structure in the
vicinity of damaged wood and shelter tubes. Above ground stations initially
contain bait.
It is very important that bait systems are properly
installed and diligently serviced. Monthly inspections of a baiting system
usually are necessary, except during inclement winter weather. Successful termite baiting necessitates
proper monitoring and maintenance of the stations.
Baits work much more slowly than soil termiticides,
and the homeowner should be aware of the possibility of a lengthy baiting
process. Several months or more may elapse before the termites locate stations.
Then termites must feed on sufficient amounts of the toxicant for the desired
effect.
An often-cited advantage of termite baits is that they
are "environmentally-friendly" because they use very small quantities
of chemical and decrease the potential for environmental contamination. In
addition, bait application causes little disruptive noise and disturbance
compared to soil treatments. Furthermore, baits can be used in structures with
wells or cisterns, sub-slab heating ducts, and other features that may preclude
a soil treatment. Baits are often used in sensitive environments.
A number of baits have been marketed to control
termites. Bait products that are available for licensed pest management
professionals include the Sentricon® Termite Colony Elimination System
(hexaflumuron [Recruit® II bait] or noviflumuron [Recruit® III bait]),
FirstLine® Termite Defense System (sulfluramid), Exterra® Termite Interception
and Baiting System (diflubenzuron [Labyrinth® bait]), Subterfuge® Termite Bait
(hydramethylnon), and Outpost® Termite Bait Response (diflubenzuron). Not all
of these bait systems are equally effective. It is advisable to review the
independent research that has been conducted on a particular bait, as some
products have been evaluated much more rigorously than others.
Physical
Barriers. Different
physical barriers are particularly appropriate during the preconstruction phase
to provide protection of the structure from subterranean termites. One such
physical barrier is stainless-steel wire mesh (TermiMesh®) that is fitted
around pipes, posts, or foundations. The newest physical barrier, Impasse®
Termite System, contains a liquid termiticide (lambda-cyhalothrin) locked in
between two layers of heavy plastic that is installed before the concrete slab
is poured. It is supplemented with Impasse® Termite Blocker, which uses special
fittings around plumbing and electrical pipes and conduits.
Biological Control
Agents. Certain species of parasitic round worms (nematodes)
will infest and kill termites and other soil insects. They have been promoted
and marketed by a few companies. Although effective in the laboratory, control
is often quite variable under field conditions. Limited success with nematode
treatments may be attributed to the ability of termites to recognize and
wall-off infected individuals, hence limiting the spread of nematodes
throughout the colony. Furthermore, soil moisture and soil type appear to limit
the nematode’s ability to move in the soil and locate termites.
A fungus Metarhizium anisopliae (Bio-Blast®) is
a biological termiticide that requires special application and handling
techniques. It is labeled for aboveground application to termite infestations
in structures, but it is not labeled for application to the soil. Spray
effectiveness is enhanced when applied to many foraging termites because
infected termites can pass the fungus to nest mates. However, it is difficult
to infect a large enough number of termites for the infection to spread
throughout the colony. Furthermore, it provides no long-lasting residual
activity, and the fungal spores die with the dead termites. Insufficient
research has been conducted to indicate whether this is an effective method for
controlling termites.
Building
construction. In addition to the use of chemical barriers, proper
building construction is essential to curtail infestations of these pests.
States have strict building codes that are designed partially to reduce
infestations of termites. A primary example of a situation that might lead to
subterranean termite attack would be if any wooden part of the house were to
come in direct contact with the earth. Additionally, situations such as
improperly vented crawl spaces, leaking plumbing, grading of the earth that
leads to water accumulation next to the foundation, or any other situation
which might lead to excessive moisture below the house typically are prohibited
by law.
Mound Building
Termites-Termitidae
Mound
building termites are found throught the tropical areas of the world. At maturity, a primary queen has a great
capacity to lay eggs. The queen adds an extra set of ovaries with each molt,
resulting in a greatly distended abdomen and
increased fecundity,
often reported to reach a production of more than ten thousand eggs a day for
30 years. The distended abdomen increases the queen's body length to several
times more than before mating and reduces her ability to move freely, though
attendant workers provide assistance. The queen is widely believed to be a
primary source of pheromones useful
in colony integration, and these are thought to be spread through shared
feeding (trophallaxis).
A Gigantic Queen Termite.
Image Courtesy of Brutaldeluxe
The king grows only slightly larger
after initial mating and continues to mate with the queen for life. This is
very different from ant colonies, in which a queen mates once with the male(s)
and stores the gametes for
life, and the male ants die shortly after mating.
Worker termites undertake
the labors of foraging, food storage, brood and nest maintenance, and some
defense duties in certain species. Workers are the main caste in the colony for
the digestion of cellulose in
food and are the most likely to be found in infested wood. An exception to ther termite families in the
Termitidae, which account for approximately 60% of all termite species, the
cellulite digesting flagellates have been lost and this digestive role is taken
up, in part, by a consortium of organisms.
The soldier caste has
anatomical and behavioural specializations, providing strength and armour which
are primarily useful against ant attack. Most types of Termididae have soldiers
with the ability to exude noxious liquids through either a horn-like nozzle
(nasus) or simple hole in the head (fontanelle).
Nasute Soldier Termites. Image
Courtsy Whitney Cransahaw.
The specialization of the
soldier caste is principally a defense against predation by ants. Soldiers
frequently block tunnels preventing ants from reaching the main areas of the
colony. Usually more soldiers stand by behind the initial soldier so once the
first one falls another soldier will take the place. In cases where the
intrusion is coming from a gap that is larger than the soldier's head, defense
requires special formations where soldiers form a massive like formation around the
breach and blindly bite at intruders or shoot toxic glue from the nasus. This formation involves
self-sacrifice because once the workers have repaired the breach during
fighting, no return is provided, thus leading to the death of all defenders.
Another form of self-sacrifice is performed by South-East Asian tar-baby
termites. The soldiers of this species commit suicide by autothysis -
rupturing a large gland just beneath the surface of their cuticle. The thick
yellow fluid in the gland becomes very sticky on contact with the air,
entangling ants or other insects who are trying to invade the nest.
All termites eat cellulose in
its various forms as plant fiber. Cellulose is a rich energy source (as
demonstrated by the amount of energy released when wood is burned), but remains
difficult to digest. Termites rely primarily upon symbiotic protozoa (metamonads)
such as Trichonympha,
and other microbes in
their gut to digest the cellulose for them and absorb the end products for
their own use. Gut protozoa, such as Trichonympha,
in turn rely on symbiotic bacteria embedded
on their surfaces to produce some of the necessary digestive enzymes.
This relationship is one of the finest examples of mutualism among
animals. Most so called "higher termites", especially in the Family Termitidae,
can produce their own cellulase enzymes.
However, they still retain a rich gut fauna and primarily rely upon the
bacteria. Due to closely related bacterial species, it is strongly presumed
that the termites' gut
flora
are descended from the gut flora of the
ancestral wood-eating cockroaches,
like those of the genus Cryptocercus.
Termite workers build and
maintain nests to house their colony. These are elaborate structures made using
a combination of soil, mud, chewed wood/cellulose, saliva, and faeces. A nest
has many functions such as to provide a protected living space and to collect
water through condensation. There are reproductive chambers and some species
even maintain fungal gardens which are fed on collected plant matter, providing
a nutritious mycelium on
which the colony then feeds. Nests are punctuated by a maze of tunnel-like
galleries that effectively provide air conditioning and control the CO2/O2 balance, as well as allow the termites
to move through the nest.
Termite
Mounds. Images from left to right
Courtesy of Yweny, Brian Yoon Yee Yap, Vierka
Maráková, Slovakia
Nests are commonly built underground, in
large pieces of timber, inside fallen trees or atop living trees. Some species
build nests above-ground, and they can develop into mounds (e.g. Termitidae).
Mounds (also known as
"termitaria") occur when an above-ground nest grows beyond its
initially concaling surface. They are commonly called "anthills" in
Africa and Australia, despite the technical incorrectness of that name.
In tropical
savannas the mounds may
be very large, with an extreme of 30 feet high in the case of large
conical mounds constructed by some Macrotermes species in well-wooded areas in
Africa. Six to nine feet, however, would be typical for the largest mounds in
most savannas. The shape ranges from somewhat amorphous
domes or cones usually covered in grass and/or woody shrubs, to sculptured hard
earth mounds, or a mixture of the two. Despite the irregular mound shapes, the
different species in an area can usually be identified by simply looking at the
mounds.
The sculptured mounds sometimes have
elaborate and distinctive blue forms, such as those of the compass termite
which build tall wedge-shaped mounds with the long axis oriented approximately
north-south. This orientation has been experimentally shown to help in temperature regulation.
The column of hot air rising in the
above ground mounds helps drive air circulation currents inside the
subterranean network. The structure of these mounds can be quite complex. The temperature
control is essential for
those species that cultivate fungal gardens and even for those that don't, much
effort and energy is spent maintaining the brood within a narrow temperature
range, often only plus or minus one degree C over a day.
In some parts of the African savanna, a
high density of above-ground mounds dominates the landscape. For instance, in
some parts of the Busanga
Plain area of Zambia,
small mounds of about 1 m diameter with a density of about 100 per hectare can
be seen on grassland between larger tree- and bush-covered mounds about 75 feet
in diameter with a density around 1 per hectare, and both show up well on
high-resolution satellite images taken in the wet season.
Termites are very weak and fragile
insects. They can be easily overpowered by ants and other predators when
exposed. To avoid these perils termites cover their tracks with tubing made of
feces, plant matter, and soil. Thus the termites can remain hidden and wall out
unfavorable environmental conditions. Sometimes these shelter tubes will extend
for many meters, such as up the outside of a tree reaching from the soil to
dead branch.
In many cultures, termites are used for
food (particularly the alates). The alates are nutritious, having a good store
of fat and protein, and are palatable in most species with a nutty flavour when
cooked. They are easily gathered at the beginning of the rainy season in West, Central and Southern Africa when they swarm, as they are attracted to
lights and can be gathered up when they land on nets put up around a lamp. The
wings are shed and can be removed by a technique similar to winnowing. They are best gently roasted on a hot plate or lightly fried until
slightly crisp; oil is not usually needed since their bodies are naturally high in oil.
Traditionally they make a welcome treat at the beginning of the rainy season
when livestock is lean, new crops have not yet produced food, and stored
produce from the previous growing season is running low. They are also eaten in Indonesia, including Central Java, where they are roasted or fried.
Termites can be major agricultural
pests, particularly in Africa and Asia, where crop losses can be severe.
Counterbalancing this is the greatly improved water infiltration where termite
tunnels in the soil allow rainwater to soak in deeply and help reduce runoff
and consequent soil erosion.
The US Department
of Energy is researching
ways to replace fossil fuels with renewable sources of cleaner energy,
and termites are considered a possible way to reach this goal through metagenomics.
Termites may produce up to two liters of hydrogen from digesting a single sheet of paper,
making them one of the planet's most efficient bioreactors. Termites achieve this
high degree of efficiency by exploiting the metabolic capabilities of about 200
different species of microbes that inhabit their hindguts. The microbial
community in the termite gut efficiently manufactures large quantities of
hydrogen; the complex lignocellulose polymers within wood are broken down into simple
sugars by fermenting bacteria in the termite's gut, using enzymes that produce
hydrogen as a byproduct. A second wave of bacteria uses the simple sugars and
hydrogen to make the acetate the termite requires for energy. By sequencing the
termite's microbial
community, the DOE hopes
to get a better understanding of these biochemical pathways. If it can be
determined which enzymes are used to create hydrogen, and which genes produce
them, this process could potentially be scaled up with bioreactors to generate
hydrogen from woody biomass, such as poplar, in commercial quantities.
Sceptics regard this as unlikely to
become a carbon-neutral commercial process due to the energy inputs required to
maintain the system. For decades, researchers have sought to house termites on
a commercial scale (like worm farms) to break down woody debris and paper, but
funding has been scarce and the problems of developing a continuous process
that does not disrupt the termites' homeostasis have not been overcome.
Ecologically, termites are important in nutrient recycling, habitat creation, soil formation and quality and, particularly the
winged reproductives, as food for countless predators. The role of termites in hollowing timbers and thus providing shelter
and increased wood surface areas for other creatures is critical for the
survival of a large number of timber-inhabiting species. Larger termite mounds
play a role in providing a habitat for plants and animals, especially on plains
in Africa that are seasonally inundated by a rainy season, providing a retreat above the water for smaller animals and birds,
and a growing medium for woody shrubs with root systems that cannot withstand
inundation for several weeks. In addition, scorpions, lizards, snakes, small mammals, and birds live in
abandoned or weathered mounds, and aardvarks dig substantial caves and burrows in them,
which then become homes for larger animals such as hyenas and mongooses.
As detrivores, termites clear away leaf and woody litter
and so reduce the severity of the annual bush fires in African savannas, which
are not as destructive as those in Australia and the USA.
Globally, termites are found roughly between
50 degrees North & South, with the greatest biomass in the tropics and the greatest diversity
in tropical forests and Mediterranean shrublands. Termites are also considered
to be a major source of atmospheric methane, one of the prime greenhouse gases. Termites have been common since at least the Cretaceous period. Termites also eat bone and other
parts of carcasses, and their traces have been found on dinosaur bones from the
middle Jurassic in China.
Many plants have developed effective
defenses against termites, and in most ecosystems, there is an observable balance between
the growth of plants and the feeding of termites. Defence is typically achieved
by secreting anti-feedant chemicals (such as oils, resins, and lignins) into the woody cell walls. This reduces
the ability of termites to efficiently digest the cellulose. Many of the strongly termite-resistant tree species have heartwood timber that is extremely dense (such as Eucalyptus
camaldulensis) due to
accretion of these resins. Over the years there has been considerable research
into these natural defensive chemicals with scientists seeking to add them to
timbers from susceptible trees. A commercial product, "Blockaid", has
been developed in Australia and uses a range of plant extracts to create a
paint-on nontoxic termite barrier for buildings. In 2005, a group of Australian
scientists "discovered" (announced) a treatment based on an extract
of a species of Eremophila that repels termites. Tests have shown that termites are
strongly repelled by the toxic material to the extent that they will starve
rather than consume cross treated samples. When kept in close proximity to the extract, they become disoriented and eventually
die. Scientists hope to use this toxic compound commercially to prevent termite
feeding.