In a Colombian Region, Bats Are Cacao’s Guardians Against Aggressive Pests

Cocoa has enemies. Small ones, but highly destructive. Some attack at night, such as the cocoa mirid bug (Monalonion spp.), which does not bite the leaves of this tropical tree but instead inserts its mouthparts into them and sucks out the sap. In doing so, it ruins entire crops and forces many producers to resort to insecticides. Others have bats as their allies.

That is what happens on several farms in municipalities in the department of Huila, in central Colombia, such as Rivera, Hobo, Neiva, and Gigante. Farmers there have spent years controlling these pests in another way, without spending a single peso on chemicals: by letting bats do the nighttime work.

When there are more bats in cocoa plantations, they protect them at night from arthropod pests, reducing the abundance of certain insects such as the cocoa mirid bug, an insect capable of destroying up to 80% of a harvest in just a few months. This was demonstrated by research conducted by biologist Brayan Franco Guayazan, who holds a master’s degree in Biology from the National University of Colombia (UNAL).

Pests increase when bats do not make their nighttime rounds

For one year, Franco Guayazan visited 12 cocoa farms (four sun-grown monocultures, four with simple shade, and four with complex shade), in addition to four remnants of tropical dry forest that served as comparison sites.

At each of those 16 locations, the researcher spent six nights (three during the dry season and three during the rainy season) setting up mist nets for six consecutive hours, from six in the evening until midnight, checking them every half hour to avoid harming the animals caught in them. In total, he accumulated 96 nights of fieldwork and nearly 46,656 net-hours of sampling effort, during which he captured 1,317 bats representing 25 species, according to a bulletin from the UNAL News Agency, Unimedios.

But counting bats does not prove that they are helping, so on six farms that do not use insecticides, the master’s researcher installed fishing nets around certain cocoa plants for eight weeks. These barriers allowed insects to pass through but prevented bats from entering, meaning bats could only access the plants during the daytime.

This showed that while bats were unable to make their nighttime rounds, the number of arthropods, including some potential pests, doubled on the plants (2.06 times more than on the control plants and 2.25 times more when birds and other predators were also excluded), while leaf damage increased by between 2.2 and 4 percentage points.

In addition, the greater the bat activity recorded over a plant, measured using echolocation detectors (the “radar” they use to hunt), the fewer pests and the less damage there was, especially among hemipterans, the group that includes the cocoa mirid bug and the one that showed the strongest response.

“The bats are not controlling insects at random, but rather appear to be exerting targeted pressure on the groups that represent phytosanitary risks to the crop,” the researcher explained, as quoted in the statement.

The pattern found in Huila is consistent with what has been reported in cocoa plantations in Peru, Brazil, Indonesia, and Cameroon. In Peru, bats and birds together have increased cocoa yields by as much as 119%.

This natural support is particularly beneficial for Huila, Colombia’s fourth-largest cocoa-producing department, where the National Federation of Cocoa Growers reports that 5,137 metric tons are produced annually on about 7,000 hectares. In addition, its cocoa beans are valued for their fine flavor and aroma and their low cadmium levels. Free pest control is an additional advantage for exports.

Designing forests and crops as a single system

Before conducting the net experiment, the biologist compared bat diversity in environments ranging from sun-grown monocultures to densely shaded plantations, using the forest as a reference.

The forest consistently had more species than any cocoa plantation, but the standard became more demanding when measuring how diverse the ecological roles of those species were (which ones hunt insects, which ones are large, which ones require space to maneuver): only plantations with more than 60% shade and trees of different heights and trunk sizes (plantain, poro, melina, guava, mango) achieved a diversity comparable to that of the forest.

This is important because, for bats, a cocoa plantation with young, uniformly sized trees is like a one-story building: it serves little purpose beyond passing through, whereas one with trees of different sizes offers different “floors”—cavities for roosting during the day, low branches for hunting close to the ground, and tall canopies for unobstructed flight—and that is what attracts and sustains more species.

“This changes the conversation, because it is no longer just about planting trees, but about planting them properly,” Franco Guayazan concluded in the Unimedios bulletin. “The most sensitive bats in this situation were the insectivorous species and those with larger body sizes, in other words, the very ones that play the leading role in pest control.”

In addition, the species with the highest recorded activity was Pteronotus fuscus, whose echolocation system is finely tuned to detect prey in complex vegetation and which, according to previous studies, feeds mainly on hemipterans, beetles, flies, and moths.

If the research could be translated into a single recommendation, according to the biologist it would be this: stop treating the forest and the crop as competing land uses, and start designing them as a single system. For producers, this means maintaining more than 60% shade with trees of different heights, and for those who design environmental policy, it means understanding that this effort works best when there is a nearby conserved forest to which the crop can be connected.