Biological Control: Benefits and Risks

Explained

Biological control, and why it never wipes the pest out

Biological control means using a living organism, a predator, a parasite or a pathogen, to reduce the number of a pest. Ladybirds and their larvae eating aphids is the standard example, and aphids matter because they feed on phloem sap and damage the crop.

What it does well

A control organism is usually specific, so it attacks the pest and leaves other species alone. There are no chemical residues left on the crop or washed into rivers. And because the predator breeds, the control can continue for a long time without being reapplied, which makes it cheap once it is established.

What it does not do

It works slowly, because the predator population has to build up before it makes a difference. It never removes the pest completely. And it depends on conditions such as temperature, so results vary between seasons and between sites.

The point about never removing the pest is the one worth understanding rather than memorising. If the predators ate every pest, the predators would then starve. Instead the two populations rise and fall in a repeating pattern. Pest numbers rise, predator numbers follow, pest numbers fall, predator numbers fall, and the cycle begins again. That fluctuation is the normal outcome, not a sign of failure.

The ecological risk

Introducing an organism to a new place can go badly. It may attack species other than the intended target, it may spread beyond the area where it was released, and it may itself become a pest with no predators to limit it. Because it is alive and it breeds, the decision cannot be reversed. That is the real difference from a pesticide.

Comparing it with chemical pesticides

A pesticide acts fast and kills a high proportion of the pest, which biological control cannot match. Against that, it kills useful species too, including pollinators and the pest's natural predators, it can accumulate along a food chain, it must be reapplied, and surviving pests can pass on resistance so the chemical becomes less effective over time.

A good evaluation gives one advantage and one disadvantage of each, then answers the question actually asked. Which is better depends on how quickly the crop needs protecting and how much the surrounding environment matters, and saying so is a legitimate conclusion.