The Evolution of Insect Thresholds

Index

1. Overview

2. What’s Changing?

3. Intervention Windows

   1. Economic Action Windows

   2. Predictive Pressure Indices

   3. Outcome Based Bundles

4. FMC's Integrated Approach

5. Final Thoughts

Overview

The economic threshold (ET) framework has been the backbone of integrated pest management for over 60 years. Scout the field, count the insects, and when the population crosses a line where crop damage exceeds the cost of spraying, the farmer pulls the trigger on an application. It worked well given the tools it was designed around, chemistry that kills the targeted pest, delivering near-instant death. Having a threshold for intervention tied together nicely, and still does in many instances.

However, many new products require something different.

What’s Changing?

As Pam Marrone recently noted, economic thresholds are not designed for preventative biopesticides. Many biopesticides are not rapidly killing by nature. They require earlier application, often before pest populations are even visible, or proactively as populations increase. Consider AgBiTech and their NPV products, recently acquired by BASF. For their Surtivo product (targeting pests like corn earworm, soybean looper), the stated application threshold is 5 or fewer small larvae (under half an inch) per 25 sweeps. Because the NPV works by ingestion and replication inside the larva, it's action is slow relative to a traditional synthetic product. Larvae may continue feeding for 1–3 days after becoming infected and then die within 3–9 days, with smaller larvae dying faster.

Still requiring an ET, but different than the traditional one that we might see cited by a University at say 10 larvae per 25 sweeps.

New products, such as semiochemicals and sprayable pheromones or mating disruption technologies, and digitally timed intervention programs all operate on a preventative logic that the ET model doesn’t work with.

The ET model assumes a few things:

1. pest populations are observable before economic damage occurs

2. the intervention acts fast enough to prevent that damage once triggered

3. a single decision point (spray or don't spray) captures the relevant tradeoff.

For conventional insecticides, these assumptions make sense — organophosphates, pyrethroids, and diamides deliver a rapid kill, that is also readily observable.

For biologicals, that gap stretches to days or weeks. Bt products require ingestion by early-instar larvae. Entomopathogenic fungi need time to colonize the host. Predatory insects need to establish populations. By the time a traditional ET triggers action, the biological intervention window has already closed.

Pheromone-based mating disruption operates on an entirely different plane. There is no explicit "kill" event at all. The products work by preventing reproduction before damage-causing populations ever materialize. Scouting for a threshold population to trigger a pheromone application is like checking for flood damage before buying insurance.

“Intervention Windows”

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