The social insects, ants
and bees, occupy a pinnacle of evolutionary development. They are models
of cooperation, altruism and industry. But within their lofty hierarchy
is a group with the most remarkable suite of abilities. They are the miniscule
farmers whose crop is fungi. Their multi-million member colonies tend subterranean
fungal gardens with scientific precision, applying processed green manures,
liquid fertilizers, herbicides, bactericides and even plant hormones. They
invented the micropropagation of fungi long before humans grew any crops.
Their skills; alas, earn
them no awards, just curses and poisons. Only scientists admire the leaf-cutter
ants. You'll find them interesting once you get to know them; but I do
not expect you to stop killing them.
All the fungus farmers belong
to the Tribe Attini and may be called attine ants. The taxonomic
Tribe consists of ten or eleven genera and 189 species found only in the
New World. Five genera occur in the United States, Acromyrmex (Arizona),
(Texas and Louisiana), Cyphomyrmex (southern U.S.),
(Texas) and Trachymyrmex (northern U.S.).
The actual leaf-cutting ants
are in just two of those genera, Acromyrmex and Atta.
The formidable pest in central Texas is Atta texana. Atta, boy?
In the tropics, members of
the genus Atta have been calculated to consume 12% to 17% of total
leaf production. Thus, they are the primary herbivores of those regions,
But they do provide benefits. Their aerial and subterranean actions cause
new shoot and root growth. They aerate soils to great depths and decompose
foliage most efficiently.
The subterranean gardens
of all attine ants are thought to consist of but one species of fungus,
gongylophorus, of the family
Agaricaceae. These gardens begin
with the mycelial propagules each new queen takes with her before leaving
on her nuptial flight. In the case of Atta texana, the queen is
inseminated by several males during the nocturnal nuptial flight and receives
up to one-quarter billion sperm, enough for a life-time of egg-laying.
Returning to earth, the new
queen loses her wings and begins to dig a nest from which she will never
emerge. The first worker ants crawl out in about two months, looking for
your garden. In nature, they search for leaves of broadleafed plants during
spring and early summer and consume grasses otherwise. In your landscape,
with its year-round production of foliage, they will eat leaves of dicots
(broadleafed plants) whenever it is warm enough for them to be active.
After committing defoliation,
the worker takes the disproportionately large piece of a leaf into the
nest where it is chewed into small bits which are fed to the fungus garden.
The leaf sections are fertilized with an anal secretion of the ants which
contains nutrients, as well as chemicals which encourage fungal growth
and discourage other fungal or bacterial contaminants. If all goes well,
the ants are soon feasting on gongylidia, the microscopic, balloon-like
ends of the hyphae (minute fungal filaments).
There is, at present, no
absolute eradicator of leaf-cutter ants, but we do have control measures
of a sort. If you are killing the imported red fire ant with baits like
Award or Logic, you will notice a reduction in leaf-cutter ant activity.
Many have made that observation and they keep on killing imported red fire
ants and praying for collateral damage.