Coffee Wars

A war is being waged every single day in southern Mexico. The combatant armies struggle against each other in the air, on the ground and in the trees between while forming tenuous alliances. The entangled web of violence is so complicated that sometimes one army’s alliance actually helps a completely different enemy thrive.

Day after day this dangerous dance develops, but it never ends. The players are so balanced that no single group ever gains the upper hand, which is a good thing. Their very survival depends on the war raging on, as does the battle zone – an organic coffee farm in southern Mexico.

In a new study led by John Vandermeer, professor of ecology an evolutionary biology at the University of Michigan, researchers use a decade’s worth of observations to describe a complex web of organisms that are essential to the health of the coffee farm spread out over one square mile.

The keystone of the coffee farm's balanced ecosystem, the Azteca ant.

The biggest badass in the land is the Azteca ant. It’s so tenacious that it simultaneously wages war on the lady beetle known as Azya orbigera, the phorid fly parasite and 80 other species of ants. Though they only live in three to five percent of the shade trees on the farm, no other organism thrives where they choose to nest.

Except, that is, for their partners in crime, the green coffee scale Coccus viridis; a common parasitic insect that feeds on the leaves of plants and is a known parasite to coffee plants. The two have a mutually beneficial relationship. The Azteca ants protect the green coffee scales from their major predator, the lady beetle, and in return the scales provide the ants with nutrition through the honeydew they produce.

But in a strange twist of events, the same lady beetle that can’t survive two minutes within a cluster of Azteca ants actually requires their presence to survive. Without the ants’ protection, the green coffee scale wouldn’t exist – indeed it barely does outside of the Azteca’s area of influence – and the lady beetle’s offspring would have nothing to eat.

The lady beetle predator. (a) adult, (b) larva eating a green coffe scale, (c) adult beetle being attacked by Azteca ants, (d) Azteca ant entangled by the beetle larvae.

Though the adult lady beetle is no match for the Azteca ants, their larvae can handle attacks just fine. The young beetles look like little white puffballs due to a waxy substance they create, which entangles attacking ants and allows the larvae to eat all the green coffee scales they desire. The tricky part for the beetle is laying the eggs.

Because newly hatched offspring require a lot of green coffee scales, the beetle must lay her eggs within an Azteca colony. But how is this possible when an adult beetle can’t survive the trip to make the deposit?

Parasitic fly to the rescue!

Known as a phorid, these little buggers love attacking the Azteca ants from the air. Though they can sense their presence in large numbers from a distance away, the phorids must move in close in order to locate individual ants to attack. And when they move in, all of the ants in the area react by playing possum. By waiting for this response, the lady beetle can sneak in, find a safe place to harbor the eggs and get them laid.

This delicate balance has created a spatial web of colonization. The nests of the Azteca ants are spread throughout the coffee farm, bringing balance to the entire microcosm. The flies attack the ants, the ants attack the beetles and the beetles attack the ants’ source of food. So how is this beneficial to the farm?

The green coffee scale insect, one of the many parasites of coffee plants.

The green coffee scales are a parasite to the coffee plants and would gladly eat the entire farm if left unchecked. But there are just enough lady beetles to keep them confined to the areas dominated by Azteca ants. These few areas of green coffee scales, however, are just enough for another organism called white halo fungus to thrive, which just so happens to kill another major coffee parasite known as coffee rust disease. Finally, the Azteca ants also prey on the coffee berry borer, which is – you guessed it – another big pest on coffee farms.

As intricate and well-balanced as this battle is, I didn’t even get into the full scope of it all. There are even more species of ants, some responsible for keeping other species in check and some that make it possible for the Azteca ants to form new nests. Plus, there are likely dozens of interactions that the scientists weren’t able to glimpse, even though they spent a decade watching these events play out.

In the end, this study goes to show that nature doesn’t always need our help. The coffee farm is managing to keep its parasites at bay and remain productive without the help of any chemicals or introduction of new species. Sure, the struggle may wobble from time to time and the balance of power may shift, but nature has an uncanny way of balancing it all out in the end.

This is not to say, however, that all farming should be done organically. There’s always another side of the coin. I would be very interested to learn how much coffee this farm produces when compared to another farm that uses all that modern technology has to offer.

People may not need coffee to survive, but they certainly need staples like wheat, rice, corn, and other grains, and the yields of these crops are greatly increased by modern technology. If every farm in the world were organic, even more people in the world would be starving than currently are, and even more land would have to be converted to farms in places like India and China. Without the Green Revolution and heroes like Norman Borlaug, we’d be in trouble.


About bigkingken

A science writer dedicated to proving that the Big Ten - or the Committee on Institutional Cooperation, if you will - is more than athletics.
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