Pest Control in Coffee: A Tri-trophic Comparison between a Mainland and an Island Agroecosystem

The practical requirement of pest control in agriculture is an evident application of principles of tri-trophic ecological interactions—plant (crop), herbivore (pest), and predator (natural enemy). We analyze the coffee agroecosystem and four of its main pests, the coffee berry borer, the coffee leaf miner, the green coffee scale, and the coffee leaf rust, comparing a mainland site (Mexico) and an island site (Puerto Rico). In addition to the direct trophic, competitive, and mutualistic interactions, there are a variety of indirect higher order interactions, many of which qualitatively increase the complexity of the organizational structure. We explore how the basic nodes of the natural enemy network remain relatively constant between mainland and island, but their frequency and, especially, the complications of their interconnections are dramatically different. The coffee berry borer is preyed upon by numerous species of ants at both sites with an indirect effect of larger ants interfering with smaller ants, the latter of which are able to penetrate the coffee seed through the holes the borer makes and prey on the larvae and eggs of the berry borer. While the larger ants do indeed impede the berry borer directly, their indirect effect of excluding the smaller ants counters this effect. Similarly, in Puerto Rico Anolis lizards, effective predators on the berry borer, tend to avoid areas dominated by specific species of ants, a pattern not seen at the mainland site. The coffee leaf miner is extremely common in Puerto Rico and quite rare in Mexico, for reasons unknown. Its adults are attacked by the common coqui frogs and anoline lizards, again with the indirect effect of some species of ants involved. The scale insect is common in Mexico but mainly associated with a specific species of Azteca ants, providing refuge for predatory beetle larvae and thus enhancing control of this pest across the entire landscape. In Puerto Rico the coffee leaf miner is present but only very rarely reaches pest status. The coffee leaf rust has a variety of potential biological control elements at both sites, yet only on Puerto Rico do they (the control elements) reach significant status, perhaps an element in the dramatic difference between the mainland and island site in terms of the importance of the coffee leaf rust.