BLOG:

Jun 28, 2024

Leafcutter ant fungus garden (Leucogaricus)

Leafcutter ants use the leaves they cut to cultivate a fungus called Leucoagaricus. This fungus, rather than the leaves, is their food. Escovopsis is a parasitic fungus that is harmful to both Leucoagaricus and the leafcutter ants themselves. To combat this, some ants have a bacteria called Pseudonocardia on their bodies, which protects them from pathogens like Escovopsis.

There are two main genera of leafcutter ants: Atta and Acromyrmex.

Atta: The two main species are Atta cepaholotes and Atta columbica. The Atta have many connected chambers and tunnels and heart-shaped heads. In Atta cephalotes colonies, there are >5 million ants, and the majors have small hairs. Atta columbica collonies are > 1.5 million.

Acromyrmex: The two main species are Acromyrmex echinator and Acromyrmex volcanus. This genera has a single mound. The first species is found on the ground and the second is found in trees.

We carefully excavated an Atta cephalotes and Acromyrmex volcanus colony following this procedure:

1) Dug hole 20 cm away from mound.

2) Found tunnel.

3) Found garden chamber.

4) Expose fungus garden tunnel. Cut roots away.

5) Collect fungus garden with alcohol/flame-sterilized spoon.

The layers of a fungal garden: The top is white and contains fresher fungus. The middle is green. The oldest fungus is at the bottom and is brown.

——Ant housing——! Quick summary: Mineral oil on tops, labeled, moist cotton for moisture, leaves/oats for food.

And so the experiment begins…

QUESTION: Where is Escovopsis most abundant in an ant colony?

HYPOTHESIS: Escovopsis will be present where Leucoagaricus is the freshest.

PREDICTION: If we sample the top of the fungal garden, we will grow the most Escovopsis because Escovopsis feeds on Leucoagaricus, and the top has not yet been coated in Pseudonocardia.

EXPERIMENTAL DESIGN:

    Variables:

        Independent Variable: section of the fungal garden

        Dependent Variable: Escovopsis growth

    Controls:

       Positive Control: culture of pure Escovopsis

       Negative Control: no fungal garden particles

CONTINUED PROCEDURE:

1) Extract ant colony: Atta cephalotes.

2) Take 5 pieces (about the size of half a grain of rice) from the top layer of the colony and place in each section of the PDA (potato dextrose agar) plates. Repeat three times for all three top layer plates.

3) Repeat step 2 for middle, bottom layer, and waste pile.

RESULTS:

Contrary to our hypothesis, the samples of the middle layer actually had the highest number of colonies on our PDA plates. Escovopsis thrives in the middle layer because that’s where the concentration of Leucogaricus is the highest, and this parasitic fungus feeds off the ants’ food. The bottom layer contains a lot of their waste, which is not a suitable environment for the Escovopsis, and the top layer is coated with the Pseudonocardia, which has antibiotic properties, from the ants’ bodies.