The Sri Lankan Beetle Your Salad Depends On
Pesticides killing dung beetles on Sri Lankan tea plantations degrade soil fertility, erasing short-term pest-control gains with long-term agricultural losses.
When pesticides applied to Sri Lankan tea plantations killed dung beetles, the collateral damage extended far beyond the intended pest. These beetles are essential for soil health—they bury animal waste, lock nitrogen into the soil, and maintain soil structure. Without them, organic matter collapses and fertility plummets, requiring more fertilizer and ultimately erasing the economic gains from pest suppression. The case illustrates how agricultural cost-benefit analyses that ignore ecological interdependencies systematically underestimate the true price of chemical interventions.
In 2018, entomologist G. V. P. Reddy documented what happened when a standard pesticide was applied across tea plantations in Sri Lanka. The intended target was a leaf‑eating pest. The unintended casualty was the dung beetle. Dung beetles bury and break down animal waste, locking nitrogen into the soil and building its structure. Remove them, and dung sits on the surface—nitrogen volatilises, organic matter collapses. Reddy’s data showed that the indirect yield penalty from degraded soil erased the short-term gain from pest suppression. The pest-control benefit was real, but the hidden cost—lower soil fertility, more fertiliser needed later—ate into profit. The default assumption is that a pesticide harms only pests. In manufacturing terms, that’s an untested tolerance: believing a chemical touches exactly one variable. Here, it knocked out a critical biological fixture. The failure mode wasn’t the pest; it was the fertility engine. Nobody is saying stop managing pests. But when the cost analysis stops at the pest, it misses the scrap that gets created underground. When the beetles stop working, the real bill shows up at harvest.