Agriculture Reference
In-Depth Information
and the latter as temporal castes. Physiological castes are defined in relation to a major
physiological state that may also be related to age or anatomy. With the exception of
the males, castes appear to be determined on the basis of colony needs rather than a
genetic basis.
The following castes and other adult forms are to be found among the ants.
Males.
With fewexceptions, the males fulfil no defined productive role within the ant
colony and their role is purely a reproductive one.
Queen.
The queen (orgyne) is the principal female reproductive of the colony and, in
most species, is winged with a large gaster and a fully-developed hymenopteran thorax.
Wings are shed early in the process of colony founding. In contrast, among the army ants,
the queens are blind and wingless with a reduced thorax (dichthadiiform). The wings of
certain social parasitic ants are also much reduced and non-functional.
Workers.
The workers comprise the wingless female caste in the ants. With few exceptions,
they are sterile and have reduced or no ovarioles. In contrast to the queen, the workers
have a simple thorax consistent with their lack of wings.
The worker caste may be subdivided into major, media and minor sub-castes on
the basis of size, each of which may have defined behavioural roles. Where the major
worker is highly specialised for fighting, she is known as a soldier. Such specialisations
may include modifications to the mandibles to form sickle- or hatchet-like organs more
effective in fighting. A further specialisation is phragmosis, or the gross enlargement
of the whole head leading to a massive structure which is used to block passages
within the nests thereby denying access to enemies. In some species, the gaster may be
similarly modified for blocking.
Ergatogynes.
These are non-reproductive forms intermediate between the workers and
the queen and occur in two forms namely, intercastes and ergatoid queens. The intercastes
occur in a graded series and are present in conjunction with the workers and the queens;
they lack spermathecae and are therefore unable to mate. In contrast, the ergatogynes or
ergatoid queens can replace the queen and do not form pan of a graded series. They are
most common in primitive ants and possess functional spermathecae.
Gamergates.
Thesecomprise a true physiological caste that occurs in some of the
ponerine ants where the queen is replaced by fertile, worker-like forms.
In addition to the gamergates, two further physiological castes are of interest.
The first of these is the 'replete' or 'honey pot' ant in which some of the major
workers have become specialised for the storage of liquid food (as sugar solutions) and
water through enormous dilation of the gaster. These occur in the families
Dolichoderinae and Formicinae and appears to be an adaptation to the unfavourable
conditions pertaining in such harsh habitats as deserts. A physiological caste occurs in
certain granivorous ant genera (
e.g., Pheidole, Acanthomyrmex
) in which seeds consti-
tute a substantial pan of the diet. As a specialisation for milling seeds, the head is
grossly enlarged relative to body size to accommodate the enormous mandibles and their
