Like ants, wasps and bees, termites are social
insects. They exhibit brood care within their
social community or "colony". A colony is
really just a very large family of insects.
Within this family there is an overlap of parent
and offspring generations. Some of the
offspring diverge from the normal course of
development to become various castes. Unlike
most insects, which have only one linear
developmental pathway, termites have branching
developmental pathways. Therefore, we say that
they are polymorphic.
The family.
Termites are said to live in "colonies" but this
is misleading. A colony is really just a family
of insects. One of the most profound and
defining attributes of the termite family is
that it is built on monogamy. Termites are
faithful. They are probably the most monogamous
group of animals on earth. The evolutionary
outcome of this commitment to monogamy is a
large and integrated family. As far as
biologists know, termite colonies are the most
sophisticated families ever to evolve in the
universe. Human families are not nearly as
advanced. Humans, in contrast to termites, have
the most advanced, non-family based type of
social system known in the universe.
Termite colonies are comprised of three basic
castes: workers, soldiers, and reproductives.
Eggs hatch into tiny immatures incapable
of feeding called larvae. Larvae are totipotent
which means that they are genetically capable of
developing into any caste. Time of year, diet,
and pheromones all play a role in determining
which developmental pathway any given termite
follows.
Workers comprise the bulk of the
population. In lower termites there is a false
worker caste called pseudergates who retain the
potential to become alates. Workers feed all
the dependent castes: larvae, nymphs, soldiers
and reproductives. They also dig tunnels,
locate food and water, maintain colony
atmospheric homeostasis, and build and repair
the nest. In some species their job description
also includes mushroom gardening.
Soldiers develop from nymphs,
pseudergates, or workers. The metamorphosis to
a soldier takes two moults. The transition
stage is called a presoldier. With their
specialized defensive weaponry, soldiers provide
colony defence against numerous predators such
as ants and centipedes.
Reproductives develop either from alates
or neotenics. Alates are winged termites. Each
species produces a cohort of alates at a
particular season. The alates of each species
fly at a unique time of day and under specific
conditions. In Toronto, the alates of
Reticulitermes flavipes appear from February
through May and usually fly about midday on warm
days. The alates develop from nymphs by growing
wings and compound eyes. After flying, the
alates break off their wings along a basal
suture and are then called dealates. Dealates
form tandem courtship pairs, and after a brief
courtship run, dig into the soil adjacent to
wood, mate, and start a family. The offspring
constitute the colony. The founding
reproductive pair is now the queen and king of
the new colony.
Primary reproductive females, or queens,
vary in size depending on the species.
Tropical queens may measure 10 centimetres in
length and produce thousands of eggs a day. The
enlarged abdomen makes her relatively immobile
and dependent on the workers. She is licked and
fed constantly and closely attended by her
relatively small mate, the king. There is
usually just one pair of primary reproductives
per colony but some species have a low incidence
of colonies with multiple reproductives
(polygamy).
Secondary reproductives maydevelop from
either unflown alates (=adultoids), nymphs (=nymphoids)
or workers (=ergatoids). If a primary
reproductives dies it is usually quickly
replaced by a secondary reproductive of the same
sex. In the more primitive, wood-inhabiting
termites large numbers of pseudergates quickly
moult to neotenics when removed from the
pheromonal inhibition of a primary
reproductive. These newly moulted neotenics
then engage in lethal fights with same sex
siblings, eventually resulting in the survival
of only one secondary replacement reproductive
of each sex. It seems surprising that these
termites which are so co-operative with their
siblings as immatures are so viscously
competitive and siblicidal upon maturation.
Unlike primary reproductives who usually
outbreed, secondary reproductives always mate
incestuously resulting in inbreeding.
Nymphoids are the most common type of
reproductive caste in species of Reticulitermes.
Termite Ecology.
Termites feed on dead plant cell wall material,
such as wood, leaf litter, roots, dead herbs and
grasses, dung, and humus. Chemically, their food
can be characterized as lignocellulosic matter,
which is the most abundant organic material in
the biosphere. Termites are able to digest
cellulose, and some species can also digest
lignin, with the assistance of symbiotic
intestinal protozoa and bacteria. Many termites
also have symbiotic relations with nitrogen
fixing bacteria. In converting lignocellulosic
biomass to insect biomass, termite production
supports a large proportion of tropical
vertebrate biodiversity, including many species
of amphibians, reptiles, birds, and ground
foraging insectivorous mammals. |
