Pests may be all-too-familiar occurrence on coffee farms, but, according to recent research for agroecologists, they don’t need to be. Agroecologists, people who study ecosystems in agriculture, are discovering complex systems of pests, their predators and fungi that interact on a micro- and macro- scale to keep insect, fungal and bacterial populations in check.
The Coffee Berry Borer
The coffee berry borer (CBB) is a ubiquitous coffee pest known to everyone from producers to roasters. Though this malignant insect is tiny at just 1.5 millimetres long, it packs a deadly punch. CBB can infect nearly 100% of cherry on a farm and result in an average of 30-35% loss of annual crop. A farmer’s income can be further damaged by decreased quality in the remaining cherry that makes through the harvest.
CBB affects coffee cherry primarily when the female bores a single hole through the skin of the cherry into the seed. Once inside, she bores many smaller tunnels inside the seed and lays her eggs along these tunnels. When the eggs hatch in larvae, they gorge on the seed and cherry before leaving the cherry to mate and later lay their own eggs in other coffee cherries.
There are three primary ways that the hole the insect makes can lead to problems with coffee quality and annual yield. Cherry can fall on the ground before it reaches peak ripeness and rot on the ground, reducing harvest size. The holes in the cherry caused by the female borer can make seeds more susceptible to fungal and bacterial growth that can affect cup quality. Finally, holes bored earlier in the cherry growth cycle can stunt fruit growth and cause lower density seeds, which reduces both the size and quality of the crop.
Since CBB’s first appearance in the 1910s, it has spread across the world and remains a constant threat for coffee farmers globally. Annually, damages from this tiny insect can be in excess of $500 million.
However, some farmers and farming communities seem to be far more successful at keeping CBB in check. Professor of Ecology and Evolutionary Biology at the University of Michigan, John Vandermeer, Ph.D., researches agroecosystems on coffee farms and he’s made some important discoveries about how existing coffee farm ecosystems can keep CBB, as well as other notorious coffee plagues like the leaf rust (la roya), in check. We’re going to give an overview of his findings in this article but, for those who are interested, you can find two of his related publications accessible to the public online here and here.
Vandermeer’s research takes place primarily on a 300–hectare coffee plantation in Soconusco, Chiapas, Mexico. Together with his team, he identified 13 different insects or fungi that interacted in the plantation ecosystem that kept CBB, along with other pests, in check.
The entire system of protecting, preying upon and coexisting is a complicated one. While many of the function of the ecosystem are only tangentially related protecting coffee plants, others, like those restricting the proliferation of CBB and leaf rust, have a direct impact on the success of a farmers’ crop.
In this ecosystem, the Azteca ant is a ‘keystone species’ that supports the existence of many other species in the system. Azteca ants live in clusters and occupy just 3% of the 7,000 nearby shade trees on coffee plantations.
The Azteca ant performs a number of functions in the ecosystem. One of the most important for coffee is that they prey on CBB adults and larva. They also forage cherry that falls on the ground, which serves as a refuge and breeding ground for CBB during the off season. With less cherry on the ground it is harder for CBB to find shelter and breeding areas.
Another important function of the system is the presence of white halo fungus. White halo fungus limits the expansion of the green scale bug population. Green scale bugs are coffee pests in their own right but they actually play a role in protecting coffee plants from leaf rust.
The fungus is drawn to areas with large populations of green scale bugs and, for a short time, can rage through the population, decimating their numbers. White halo fungus can destroy entire colonies of green scale bugs and keep their population in check. Most importantly, white halo fungus spores remain in the soil wherever an epidemic once raged. When coffee rust attacks trees, white halo fungus spores that live dormant in the soil nearby are attracted to and attack the coffee rust.
While Vandermeer stresses that his research is far from finished, the most salient action-point we can draw from this article is the value of planting shade trees. Ensuring abundant and diverse shade trees helps nurture ant colonies. With the ant colonies come natural systems for controlling CBB, green scale bug and leaf rust.
Shade trees can also reduce the need for artificial fertilisers, pesticides and herbicides. Shade trees are often leguminous, meaning they fix nitrogen in the soil. With natural nitrogen fixing, the need for fertiliser is reduced. Simultaneously, shade trees obscure sunlight and make it harder for weeds to grow, reducing the need for herbicides. Often, when shade trees are removed, weeds spread more quickly because they have less competition for both sunlight and nutrients. Finally, shade trees can provide a natural habitat for the insect ecosystems described above that keep a variety of pests and diseases from becoming farm-wide epidemics. As such, fewer pesticides are needed.
Shade trees offer a variety of ecosystem services that support coffee trees. In addition to reaping the rewards of ecologists’ research, we can also support such research, especially those researching direct applications to coffee farms. One way you can help support coffee research is through the World Coffee Research’s Checkoff Program.