The myth of universal strains: Can one biological control agent work everywhere?

Imagine you're a papaya farmer in a tropical, humid climate. You see a video about a biological pest control product that worked wonders in a subtropical dry zone three countries to the north. You spent good money buying it, applied it exactly according to instructions... and practically nothing happened. The pests were still there as if the treatment never occurred.

You wondered: Does the product not work? Is the pest resistant? Did I apply it wrong?

What you probably didn't know is that the microorganism inside that product is better adapted to a completely different climate than yours.

This is one of the most persistent myths in the biologicals industry: the idea that a strain should work anywhere. It's a comfortable belief for salespeople, but biology doesn't work that way.

What does "Universal Strain" actually mean?

First, let's clear up the terms. A strain is not the same as a species. You can have two strains of Beauveria bassiana, both the same fungal species, yet with biological differences so large they almost seem like different organisms.

A "universal strain" is essentially a marketing concept. What companies want to say is: "This strain worked well for us in the lab across multiple controlled scenarios, so it should work on your farm too."

Here's the problem: a laboratory is a world of controlled variables. Your farm behaves different.

Why biology works against universality

Microorganisms aren't neutral machines. They're living organisms that have evolved in specific environments, and that evolution has shaped them to be efficient, or inefficient, in different contexts.

Temperature: Different populations of Metarhizium anisopliae from different latitudes show dramatically different temperature responses. A study of 17 isolates collected at latitudes from 61°N to 54°S found that isolates from higher latitudes (like ARSEF 2038 from South Korea, strain 4295 from Australia, and 5626 from Finland) were significantly less heat-tolerant than equatorial isolates, while isolates from nearer the equator (like ARSEF 324 from northern Australia and 3609 from Thailand) tolerated 45°C for several hours. If you buy a tropical strain because it thrives at 35°C, but your region drops to 10°C in winter, that strain will be practically dormant.

Competition with local microbiota: Your soil already hosts millions of microorganisms. A "foreign" strain doesn't just need to be effective; it has to compete with native microbiota to establish itself for space and nutrients. Indigenous microbial communities, better adapted to local soil conditions, can outcompete an introduced strain regardless of how well it performed in its place of origin.

Soil pH and humidity: Every microorganism has optimal ranges. In Beauveria bassiana, both temperature and relative humidity affect virulence, and different strains have different requirements. Some Beauveria isolates achieve 100% mortality in host insects only at 90-100% relative humidity and 30°C, while success at other conditions varies significantly. Your strain might excel at 85% humidity, but if your region drops to 65% during the dry season, it simply won't perform as well.

UV tolerance and radiation: Isolates from equatorial regions, which experience intense, unfiltered UV radiation, generally show higher UV tolerance than those from higher latitudes. A study of Metarhizium strains from latitudes ranging from 61°N to 54°S documented this latitudinal pattern in UV-B response. Apply a high-latitude strain to an intense tropical sun, and you'll lose viability fast.

But then, why do some strains work in multiple places?

Here's the crucial nuance: not all strains are equal in robustness.

Some commercial strains advertised worldwide work across multiple environments not because they're "universal," but because they're sufficiently robust to tolerate variation. Or because they're sold at very high doses that compensate for mortality under non-optimal conditions.

In entomopathogenic fungi, strains selected through repeated exposure to abiotic stress, variable temperature, UV radiation, shifting humidity, can become more versatile in the field. Researchers describe these as "adjusted environmental stress responses": conidia produced under abiotic and biotic stress can withstand a broader environmental range, and improve virulence against insects. But this still operates within a range, not universally. A strain robust from 20-35°C won't function well at 10°C or 45°C.

When an "Imported" strain makes sense (and when it doesn't)

It makes sense if:

• The target environment is similar to the strain's origin (comparable climate, soil type)
• It's a strain validated across multiple environments under real field stress, not just lab conditions
• The pest species also matches (some strains have host preferences)
• You're willing to apply higher doses to compensate for local microbial competition
• You have baseline data on application rates for your specific conditions

It doesn't make sense if:

• Your climate is radically different from where the strain originated
• Your soil pH, organic matter, or microbial community is vastly different
• You're seeking a low-cost product (because environmental mismatch means more failures, offsetting any price savings)
• You need consistent, predictable results and cannot absorb failure risk

The case for local strains (without romanticizing)

The LUBILOSA program (Lutte Biologique contre les Locustes et Sauteriaux) offers a clear example of why local strain selection matters in biological control. In 1980, faced with devastating locust and grasshopper outbreaks across Africa and the limitations of synthetic insecticides, researchers needed a biological alternative that could actually work in African field conditions. Generic Metarhizium strains were not enough. The breakthrough came when CABI Bioscience collected a specific isolate of Metarhizium acridum (strain IMI 330189) in Niamey, Niger, in 1988, from an African grasshopper species. This African strain, adapted to African conditions, became the active ingredient of "Green Muscle," registered for use against the brown locust in South Africa in 1998, and against desert locusts and grasshoppers in nine Sahelian countries in 2001.

The payoff of that local selection is measurable. Field trials showed up to 98% mortality of brown locusts within three weeks. During the 2019-2020 locust outbreak in East Africa, Green Muscle was used to treat more than 230,000 hectares across Kenya, Uganda, South Sudan, Somalia, Ethiopia, and Tanzania, contributing to food security for an estimated 20 million people. Those numbers are not a general argument for biological pest control. They are the specific return on years of locating, isolating, and validating a strain adapted to the place where it was going to be used. A generic Metarhizium strain from another region would not have produced that result.

But here's the honest part: local adaptation comes at a cost. Isolating, validating, and scaling a regionally adapted strain takes years and significant resources. For an individual farmer, or even a small biotech startup, that is often not financially viable.

The trade-off: availability vs. adaptation

This is where the real tension sits.

Commercial, widely available strains offer consistency and accessibility. You can order them, they arrive, they've been validated in many contexts. But they may not be perfectly matched to your environment.

Locally isolated strains offer adaptation but require:

• Initial bioprospection effort (finding and isolating candidates)
• Validation under your specific conditions (months to years)
• Scale-up capacity (can you produce enough?)
• Stability over time (does the strain remain stable through generations of propagation?)

For a farmer transitioning from chemicals to biologicals, the practical choice is often the first: buy an available, well-marketed product and accept some inefficiency. For someone building a biologicals production lab or running a large commercial operation, investing in local strain validation could be the best choice.

Questions to ask before buying a strain

1. Where was this strain isolated? If it comes from a climate vastly different from yours, you already know you're taking a risk.
2. Has it been validated in field conditions in your region, or in a region with similar climate? Don't accept lab results alone. Ask for real field data.
3. How well does this strain compete against local soil microbes? When you apply a commercial strain, it has to establish itself among the microorganisms already living in your soil. Some manufacturers have tested this and can share the data.
4. What are the optimal temperature and humidity ranges? If your region regularly exceeds or falls below those ranges, you'll know immediately.
5. Does the dosage recommendation change by environment? Responsible companies understand that non-optimal conditions require higher application rates.
6. What's the shelf life, and how does it degrade in your local storage conditions? A strain robust at 25°C might lose viability fast if stored in a 35°C warehouse.
7. Have you validated it on your specific pest-crop combination? A strain effective on Spodoptera in Brazil might not be equally effective on the same pest in your region, or on a different pest entirely.

The practical middle ground

If you're working with an imported strain, here's what the science suggests:

Start small. Run trials on a portion of your operation before full commitment. Environmental surprises happen.

Collect data. Track application rates, timing, humidity, temperature, and outcomes. Over one or two seasons, you'll know if the strain matches your environment.

Don't rely on single applications. Biologicals often require repeated applications for consistency. One application of a poorly adapted strain might fail; repeated applications might work better.

Consider tank-mixing with local biology. If possible, combine the commercial strain with locally isolated microbes. This reduces your risk and sometimes creates synergy.

Ask hard questions of your supplier. If they can't tell you the strain's origin, its optimal temperature range, or its competitive ranking in real soils, that's a red flag.

Closing: what the science actually says

The uncomfortable truth is that no "universal strain" exists. What exists are strains with varying degrees of robustness, marketed with varying degrees of honesty, and applied by farmers with varying degrees of luck.

If you want better results, you have two paths:

Path 1: Invest in strains validated for your specific environment, even if they cost more. The return on investment is higher when you're not fighting your local climate.

Path 2: Understand that you're experimenting with a "foreign" strain and adjust expectations, and application rates, accordingly. Accept that some failures are part of the learning curve.

Key Takeaway

Before you buy the next biological product promising to work "everywhere," ask where its strain was isolated and what conditions it was selected for. In nature, organisms are adapted to a particular environment, not to every environment. A microbial strain is no different.