Agriculture Reference
In-Depth Information
Microcerotermes
in all except the Nearctic.
Termites are generally small insects, most ranging in length from a few millimetres
to
ca.
one centimetre and weighing from 1 to 15 mg fresh weight (Wood
et al.,
1982).
However, queens of the larger Macrotermitinae may occasionally attain nearly 12 cm
in length (Noirot, 1990) and weigh up to 56 grams (live weight) (Darlington and
Dransfield, 1987).
Termite colonies
As eusocial insects, termites are organised into colonies comprising a number of castes,
each with a discrete set of morphological and physiological specialisations tailored to
permit an efficient division of labour. Individuals pass through several larval and nymphal
stages before they reach the adult stage. Polymorphism among larvae, the ability of lar-
vae to participate in social life and neoteny (the ability of certain immatures to
reproduce) are peculiarities of termites not found in other social insects (Noirot, 1989).
The workers are defined as 'a set of more or less distinctive individuals belonging to
more than one developmental stage who contribute to such ordinary chores of the colony
as nest construction, cleaning, nursing and foraging' (Wilson, 1971). Termite workers
are also responsible for feeding the dependent castes in a process known as trophallaxis.
The latter castes include the reproductives, the soldiers and the larvae which may be fed
on salivary secretions, regurgitated food or specialised faeces. Individuals feeding on
specialised faeces are inoculated with the symbiotic protists important in digestion in the
lower termites (Waller and La Fage, 1987; Nalepa, 1994).
Termite workers change their roles as they mature (polyethism) and those in earlier
developmental stages tend to restrict their activities to brood care and inner nest activities.
In contrast, older workers are likely to be active in more 'hazardous' activities such as
repairing nests and foraging (McMahan, 1979). In the African fungus-cultivating termite
Macrotermes michaelseni,
for example, the older workers forage for food materials
outside the nest while younger workers process the forage, construct the fungus combs
and feed the dependent castes (Veivers
et al.,
1991).
The soldiers carry out defensive functions both attacking invaders of their nests and
accompanying the workers on their foraging forays. Soldiers are completely dependent
on the workers for their nutrition. The soldier head is typically elongated, heavily
sclerotised and most possess large, forwardly-directed mandibles. In one subfamily of
the higher termites (Nasutitermitinae), the head is elongate forming a snout from which
irritant and entangling chemicals are sprayed onto their enemies. Defensive chemicals
are produced from the frontal and salivary glands.
The queen and king are the primary reproductives. They normally develop in the parent
nest as specialised reproductive nymphs (higher termites) and from the general worker
nymphs (in the lower termites). At certain times of year, mature individuals leave the nest
in one or several swarms and after pairing, establish new colonies. Following colony
establishment and particularly in the higher termites, the queen's abdomen swells
enormously and she becomes a veritable egg factory. Production rates as high as 18,000
to 43,000 eggs per day have been estimated for the queens of certain Macrotermitinae
(Grassé, 1984); while such rates are probably variable over time, lifetime production
must be many millions. Queens are less fecund in the lower termites (Noirot, 1990).
