Johannes Füssel, 1993
www.eco~tierra.com, 2001
Nindirí - Masaya, Nicaragua
| Brief Ecology of Leaf Cutting Ants and Utility of the Canavalia Bean | How To Do It | References |
Leaf cutting ants (Atta spp.) are a major
problem in establishing agroforestry plantations,
particularly in systems of low external input
or organic production, where the use of agrochemicals
is restricted or prohibited. Furthermore,
to date agrochemicals have not offered a
very effective way to control leaf cutting
ants in the long run, are expensive for smallholders
and difficult to manage, because the majority
of these are poisonous for both men and animals
(e.g. chicken may die, if they pick up the
grain).
During several years of consultancy for the
Ministry of Environment and Natural Resources
in Managua, the author managed a number of
experimental and demonstration plots, where
the principles of a low external input agroforestry
was applied. The major problem was the control
of leaf cutting ants without the use of agrochemicals,
over all in the protection of neem trees
(Azadirachta indica A.Juss.). The canavalia bean (Canavalia ensiformis (L.) DC.) offered an excellent and effective
way to combat these insects.
Leaf cutting ants do not cut leaves as a
food source, but use this material to cultivate
a fungus, which serves them as food. For
this reason, the insecticidal properties
of neem do not affect the ants, although
they may poison their fungus cultivation,
essential for their survival, with canavalia.
The fungus is cultivated in caves at a depth
of 50 cm - 150 cm with an diameter of 20
cm - 100 cm. The caves normally have several
(3 - 8) entrances and narrow passages (5
mm), purposely well hidden, with a preference
among stones or with earth and organic matter.
Occasionally the entrances are bell-shaped
with very large diameters up to 120 cm and
in no way hidden.
The canavalia is a Fabaceae, order Leguminales,
growing shrubbery, winding to a height of
up to 12 m (Franke, 1976), but once pruned
the shoot presents little problem in crops.
The mature pods measure up to 70 cm (15 cm
- 30 cm long, 3 cm - 4 cm wide) and contain
10 - 15 large white seeds, of 25.5 % proteins
and, among others, the poison canavalin,
an atypical amino acid (Franke, 1976). The
yield is 8 - 40 dt/ha (Franke, 1976). The
plant is highly drought resistant and is
an excellent cover crop, living manure and
mulch (40 - 50 t/ha), growing on almost any
soil in tropical climates up to altitude
to 1.800 m (NAS, 1979). Livestock feed on
it for necessity, e.g. in times of drought.
The green seeds and pods are digestible and
contain apr. 22 % proteins, but due to their
content of canavalin, the water in which
they are boiled in, must be discarded (NAS,
1979). The tender pods are particularly delicious.
Taste them like vegetable, in soups or prepared
like 'French beans': once cooked one fry
them in butter, with salt and grounded bread
added. Or prepared to a salad: the tender
green pods once cooked, can be chopped with
onions. Vinegar and salt added to taste.
To eliminate the fungus in the ant's burrows,
four methods were tried:
Offering to the ants canavalia leaves, placing
the cutted leaves near to the entrances of
the burrows, works well, although only until
they learn, that the canavalia does nothing
good to their fungus crop. Therefore, the
canavalia bean must be cultivated away (50
m) of the ant's burrows, and need to be placed
at all the entrances of the cave simultaneously.
The second method is much more secure, if
the liquid penetrates well into the cave.
One needs to prepare appr. 2.5 kg leaves,
liquefied in 40 l of water and pour it into
the holes. Using this method, all 35 caves,
where the liquid penetrated well, were eliminated.
But when the liquid did not penetrate well,
only 42 % of the 12 caves were successfully
destroyed.
Canavalia may be cultivated directly above
the ant's caves, in association or rotation
with other crops or in controlled fallow,
where, by luck or by purpose, the canavalia
grows above a cave. The system works fine,
if the density of the plants above the caves
is sufficiently high (apr. 25 seeds/m2 = 5.5 dt/ha); but still with a quite low
density (appr. 9 seeds/m2 = 2 dt/ha), 83 % out of 82 caves were eliminated
successfully (Pineda, 1995).
Broadcasting the seed (covered beans or tapped
beans) is a traditional practice in many
parts of Central America, particularly on
very rough lands. It conserves the soil and
to saves manpower, obtaining very good yields,
in case the vegetation is sufficiently developed
to tap the seed (Hesse-Rodrigez, 1994). Since
the canavalia have rather big seeds, this
specie serves perfectly well for this type
of sowing. Pineda (1995) eliminated on a
1.5 ha terrain, 83 % out of 82 leave cutting
ant's burrows, using a density of appr. 2
dt/ha.
In humid conditions, the canavalia bean can
be sown in developed vegetation, which may
be cut down the same day for best results.
If the rains do not fail, this type of sowing
works very well on bare ground too, without
any problems.
Acknowledgement
to Robert Babington Smith for proof-reading
this text
References
Franke W (1976) Nutzpflanzenkunde. G. Thieme
Verlag, Stuttgart, RFA. 467pp
Hesse-Rodrígez M (1994) Sembradores de esperanza.
Editoral Guaymuras y COMUNICA, Apdo. 1843,
Tegucigalpa. 253pp
NAS - National Academy of Science - (1979)
Tropical Legumes. National Academy Press,
Washington, D.C. 332pp
Pineda D (1995) PROCONDEMA, Choluteca, Honduras.
Personal communication
| Brief Ecology of Leaf Cutting Ants and Utility of the Canavalia Bean | How To Do It | References |