CASE STUDIES 
DRYWOOD TERMITES
TERMITES OF CALIFORNIA
Wood-boring insects may be
grouped conveniently into those which damage: 1)
standing trees or newly felled logs; 2) sawn timber and
wood products during seasoning or storage; and 3) wood in
use. They may also be further grouped as to whether they
attack hardwoods or softwoods or attack heartwood or
sapwood. Certain insect species attack more than one of
these groups.
Three things are necessary
for insect attack - a source from which the infestation
spreads, susceptible wood, and suitable conditions of
temperature and humidity. Relatively little is known about
some factors which make certain woods more attractive to
insects than others, but insects are often quite
selective. Fungal decay in wood often renders it more
susceptible to infestation, but may also repel insects.
Some insects may tolerate wide ranges of physical
conditions; others cannot survive great fluctuations in
temperature or humidity. Prevention of attack by insects
is sometimes closely related to the proper handling of
lumber during milling and storage,
Signs
of damage. Insect attack is generally characterized by
tunnels or cavities (often containing wood powder or fecal
pellets) within the wood. In many cases there are holes of
various shapes and sizes on the surface. The wood powder (frass)
may be pushed out through the holes, forming small piles
beneath or on the surface of infested wood, indicating
that adults have emerged recently or that live insects are
working inside the wood. Sometimes, when attack is severe,
the wood may be reduced to a hollow shell or to a powdery
condition. In other cases, there may be very little
external evidence of attack, and the interior condition of
the wood can only be determined by probing with a sharp
instrument or by striking or pounding the surface
(sounding) to detect hollows by sound differences.
No part of the United
States is completely free from wood-destroying insects.
The problem in Alaska is so small as not to warrant
concern. The problems in tropical and semi-tropical areas
are at the opposite end of the spectrum.
Potential economic losses
and significance of the damage inflicted, as well as
appropriate control measures, depend upon the type of pest
involved. It is therefore essential to accurately identify
the cause of the damage and to distinguish insect damage
from other factors involved in the deterioration of wood.
Failure to appreciate these points often results in
unnecessary treatments.
The subterranean termite,
(see example), the drywood termite, (see example), and the
dampwood termite, (see example) are the three types of
termites common in California. Different types are more
prevalent in different areas. Example, i.e., dampwood
termites in northern coastal area, drywood termites in
southern California. Pest control operators must have
knowledge of all types and should be aware that rare
infestations of other types of termites can occur in their
area.
Subterranean termites are
the smallest in size but the most destructive and
numerous. Drywoods are mid sized and probably the most
costly to control. Dampwoods are the largest and probably
the easiest to control. Termites have incomplete
metamorphosis. They hatch from eggs as “nymphs” and need
the adults to attend to the eggs. They go through seven
instar molts. Some then change to soldiers or swarmers
“alates’t There is no worker class in the
drywood or dampwood termites. All of the nymphs become
soldiers or swarmers and the nymphs do the work of the
workers in the colony.
All termites convert
cellulose to starch by protozoa in the gut. They must get
protozoa from other members of the colony. When the colony
gets larger, the food supply is short, or conditions
change, swarming occurs. This swarming usually occurs in
the spring or fall for subs and dampwoods after a rain or
on a bright clear day. Drywood termites normally swarm mid
day in the fall, Sept. to Nov. Termite swarmers are poor
fliers and usually travel a very short distance. On
landing, they shed their wings, mate and start a new
colony.
Termite workers are cream
colored with no wings and no mandibles. Subterranean
termite swarmers are black. Drywood termites and dampwood
termites are reddish brown and either have wings or wing
pads. Dampwood termite wings are much longer than the body
of the termite. Soldiers can be identified by the big head
and mandibles. Drywood termites can exist in wood with a
moisture content as low as 3%.
The genus of drywood
termites were recently split off. The western termite
formally called kalotermes are now called incisitermes
minor hagen. Termites work around the clock. Subterranean
termite workers live from 3 to 5 years. Queens and
supplemental reproductives live longer.
Several reasons that
termites are destructive:
1. The individuals are
long lived.
2. The colony is
self-perpetuating.
3. They have a constant
source of food.
4. They are social insects
and thus cooperate.
5. They are protected from
extremes of heat and cold and from their enemies by their
cryptobiotic mode of life: all of which results in
constant increase in destructive powers. A termite is an
insect with three body segments, head, thorax and abdomen;
four equalized wings, with six legs attached to the thorax
and with a pair of beaded antennae. Of the major
constituents of wood, cellulose is readily digested by the
enzymes of protozoa living in the digestive tracts of
termites, whereas lignin is entirely indigestible, so that
wood with high lignin contents is invariable avoided.
Sapwood is more attractive than heartwood. The lower
intestine of the termite contains a swarming mass of one
celled protozoa. These minute protozoa contain enzymes
which digest the wood fragments. If their protozoa are
removed, the termites die of starvation. The highly
specialized king, queen, soldiers and the first instars
depend upon nymphs and workers for their feeding. If these
dependent individuals are isolated, they starve since they
are unable to feed themselves.
Termites aid in the
dissemination of fungi by providing shelter and humid
atmosphere necessary to fungi growth. Fungi renders
certain services to the termites:
1. The fungus provides
moisture for the termite when consumed.
2. Fungi may be of some
value to termites in the preliminary softening of wood.
3. Fungi provide a supply
of protein and vitamins for the termite.
Termites clean themselves
by licking or grooming one another. This results in each
termite consuming the secretions of the other. While the
grooming is going on, the termites exchange nourishment by
mouth. This exchange of nourishment is known as
trophallaxis.
Termites have a caste
system in their colonies. Subterranean termites have
reproductives, workers and soldiers and swarmers whereas
dampwood and drywood termites lack a true worker caste,
their immature nymphs do the work of the colony. The
reproductive caste consists of male and female. The male
termite mates throughout his life with the queen. These
reproductives swarm at certain times of the year.
Subterranean termites swarm both in the spring and the
fall whereas the main swarming of drywoods occurs in the
fall. Swarming usually occurs just after a rain when the
sun shines brightly.
The average soldier or
worker lives only two or three years but queens may live
much longer.
There may be several
supplementary queens in each colony. These supplementary
queens readily replace the primary queens when the latter
die or are injured. The supplementanes are important
because they rapidly increase the termite population.
Termites as a rule avoid light and seek narrow cracks and
crevices. The winged reproductives may wait three months
or more for correct atmospheric conditions before
swarming, especially as far as temperature and humidity
are concerned. The alates or winged reproductives then
completely reverse their instincts and seek light and open
spaces. The flight is short and weak. The termite wings
break off at a fracture point, the termites pair off,
mate, and form a new colony.
The worker is the form
which does all of the work of the colony such as
constructing tunnels, excavating chambers, cultivating
fungus gardens, obtaining food, feeding the young, the
soldiers, and the king and queen. The sole purpose of the
soldier termite is that of defense of the colony
particularly against their arch enemy, the ant.
Termites are world wide in
distribution but are absent from the arctic and antarctic
areas. Some
1,800 species of termites
have been identified. There are approximately 45 species
in the United
States.
(RETICULITERMES
HESPERUS)
The subterranean termites
are ground dwelling termites which nest in the soil, or in
the wood or vegetable material in contact with the ground.
They are able to reach wood or cellulose material above
the ground level by means of earthen tubes which they
build. Since these termites are dependent on soil
moisture, they must usually have a ground connection.
There are rare exceptions where they have been able to
maintain themselves in damp wood with moisture at or
greater than 14% even after the ground connection was
broken. Unlike drywood and dampwood termites, their feces
consist of liquid drops, not pellets, which
characteristically spot their excavations in wood. In
their galleries frass is also characteristic. The frass
consists of masticated wood and earth cemented together
with saliva and liquid feces to form a mud-like cement.
The sexually mature
reproductives, known commonly as swarmers, bunch up inside
to the nest near the exit hole. When the right combination
of moisture, temperature, and light intensity is present,
they swarm out of the colony and fly away to form a new
colony. Swarmers are not given off from a western
subterranean termite colony until after the colony is at
least 2 to 3 years old.
After the male and female
reproductives (Alates) have swarmed from a colony, they
pair off and attempt to establish a colony of their own.
The successful pairs manage to excavate a cell. They seal
the exit with bits of debris cemented together with the
liquid fecal material. Copulation takes place only after
this cell is prepared and sealed closed. The male (king)
cohabits with the female (queen) throughout the life of
the colony.
When a subterranean
termite is hatched from the egg, it is called the First
Instar Nymph. When it molts (sheds its exoskeleton) for
the first time, it becomes a second instar nymph. If the
individual is destined to become a reproductive (alate),
it will shed its skeleton six separate times to finally
become a seventh instar stage which is the fully developed
reproductive stage (swarmer or alate). After the fourth
instar stage has been reached, those nymphs that are
destined to become reproductives start to grow wing pads
and otherwise differentiate from the worker caste. At each
succeeding instar stage, the wings become more fully
developed until they are quite well developed. Another
molt and this individual will be a fully developed swarmer
capable of mating and forming a new colony. A new colony
does not produce swarmers until after its third year. In
an older colony, the transition from egg to adult usually
takes from one to two years. Termites will eat anything
made of cellulose. In addition to wooden members of the
house, this includes books, other paper products, and
furniture. Any structure can be easily invaded by
subterranean termites.
(INCISITERIVIES
MINOR
HAGEN)
Termites are called social
insects because they live together in colonies. Drywood
termite colonies contain three types of individuals, each
of which has its own characteristic appearance and its own
duties to perform within the colony. The colony prospers
as a whole because each of the “castes” (type of
individuals) contributes to the welfare of the colony by
performing its own duties.
The first types of
individuals are the Alates or Swarmers. These are the
mature males and females ready to swarm out to start new
colonies.
The second type of
individual is the soldier. The main function of the
soldier termite is defense of the colony against intrusion
by ants and other enemies.
All the rest of the
individuals are nymphs. They perform most of the work of
the colony other than reproduction and defense.
Drywood termites do very
well in Douglas fir and all kinds of pine as well as most
other woods used in the structure of houses. They do well
in redwood, contrary to popular superstition. They are
frequently found “in nature” in English walnut,
eucalyptus, and citrus trees, just to name a few of the
ornamental and fruit trees they infest.
Drywood termites are
completely independent of the soil and thus do not have
tubes extending to and from the soil. They can thrive
readily in the dry timbers of a structure without
requiring any additional moisture. Drywood termites move
with and across the grain of wood.
Drywood termite pellets
have longitudinal grooves. These are characteristic of
drywood termite pellets and may be used in identification
to differentiate them from beetle pellets which are
“smooth”, having no grooves.
(ZOOTERMOPSIS
ANGUSTICOLLIS)
This is the largest
species (in size) of termites we will be concerned with.
It sometimes will reach a length of one inch. It is also
of the least economic importance of the three termites we
are discussing.
In their role as wood
destroyers, dampwood termites are associated with
excessive moisture conditions. Their environment is
enhanced by the presence of excessive moisture, whether
derived directly from the ground as in a forest situation,
from the ground due to faulty construction in the case of
a residence, or from a leaking pipe, clogged roof drain,
inadequately engineered cooling system run-off, faulty
grade level condition, or other man made moisture
conditions.
Dampwood termites are
found along the Pacific
Coast from Canada down through
California to Mexico. Infestations are found all the way
from sea level to six thousand feet in elevation. Dampwood
termite colonies in the understructures of houses are
found in the structural timbers that are, for one reason
or another, exposed to excessive moisture conditions.
These conditions might be caused by a simple earth to wood
contact as might be found where a supporting post for an
outside porch extends directly into the soil or when a
structural beam underneath the house is directly in
contact with the soil of an earth filled porch. Sometimes
these colonies are found under the bathroom area where a
leaky bathtub or toilet produces a continuous or frequent
source of moisture. An excessive moisture condition under
the house may even be caused by inadequate ventilation due
to lack of or insufficient number of foundation vents to
allow free circulation of air.
Dampwood termites, like
drywood termites, do not have a true worker caste in their
colonies. The work of the colony is performed by nymphs
which later become either soldiers or swarmers (male or
female). Swarming occurs from July through October,
usually occurring around September.
The queen will lay from 6
to 22 eggs at a time, averaging 12. The second lot is laid
the next spring. Although the queen of this species is not
a great egg layer, some colonies are known to have up to
4,000 individuals. This is probably due to a large number
of supplementary reproductives being present in the
colony.
The tunnels of these
insects are of many sizes and shapes, having a velvety
appearance in the runways. This surface may be covered
with dried liquid feces. The pellets are deposited in
dumps or clusters in the galleries usually and may have a
slightly hexagonal shape. The color of the pellets will
vary with the type of wood being eaten. The pellets have a
great resemblance to dried coffee grounds. This insect
will eat sound wood as well as damp wood.
DRYWOOD TERMITES
SUBTERRANEAN TERMITES
DAMPWOOD TERMITES
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