New York State IPM Program

The 80/20 Rule of Pest Activity

When a pest problem begins in an office or workshop, it might seem like the entire place is overrun. But more often the pests are feeding and breeding in just a few confined areas — making there way from there to other parts of the building. Pest managers call this the 80/20 rule, meaning that 80 percent of pest problems come from 20 percent of the area.

These two cases highlight the 80/20 rule:

Case One. The scene — a small office in a corporate building. What started as a few flies in the waiting room quickly escalated to hordes of flies around computers, lights, equipment — and guests — in every part of the office. These were Phorid flies — small, 1/8 to 1/4 inch long, but annoying nonetheless. How to ID them? For starters, they’re humpbacked and their wings have distinctive veins. They like to breed in rich organic material.

Our inspection took us to a part of the building that had been vacated several months prior — and we quickly found our problem’s source in an empty office, where swarms of flies surrounded a closed trashcan.

Spillage from the can had dried on the floor. And inside? Thousands of fly larvae and pupae — breeding in food discarded from a refrigerator emptied months before. This single trashcan was responsible for flies throughout the building.  The trashcan was bagged and removed, and sticky traps with an attractant captured the flies. Case closed.

Case Two: The scene — a school with an ongoing cockroach problem. Sightings had dropped dramatically over time, but still — building managers wanted to stay ahead of the game with proactive control measures. Our inspection found a few conditions conducive to pests, but none accounted for the large numbers of cockroaches previously seen.

Then — in a tucked-away part of the building, up a ladder and through a closed door, we came to a storage room. The place was littered with piles of frass (insect droppings) — which told us this area had

once hosted a large cockroach population. On the floor was dried sewage from an old leaky pipe, one that had recently been replaced. We had found the breeding and harborage site that attracted cockroaches in the first place.

The takeaway? If you have an abundance of pests, remember — the source is often in those areas that are out of sight, difficult to access, or otherwise hard to clean.

Author: Matt Frye

An IPM Extension Educator stationed in the Hudson Valley, Matt offers advice, training sessions, workshops and conducts research related to pest management in and around buildings.

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