Cheap chemical pesticides are expert at wiping out millions of insects with a few hundreds dollars worth of chemicals. Yet as the health and environmental costs of pesticides mounts, and resistance against pesticides is on the rise after decades of chemical warfare in the fields, the equation is looking a little different.

Hence renewed interest in biopesticides. Harnessing the armory nature has given to bacteria, fungi, and even other plants allows researchers to redirect the sophisticated strategies species have evolved over millions of years to protect crops in the field.

An estimated 80% of the treated insects died within one to three weeks.

Fungi, in particular, have proven to be agricultural mercenaries. Applied at the right time, with the right treatment, fungal spores can cut down armies of insects–such as the application of Green Muscle over 10,000 hectares in Tanzania in 2009. Trillions of specialized fungal cells called “conidia” from the fungus Metarhizium anisopliae were sprayed in a solution with mineral oil to weaken the locusts devouring crops in East and Southern Africa. An estimated 80% of the treated insects died within one to three weeks. Other animals were unharmed. And the biopesticide (developed through a public-private partnership among governments and aid donors) continued working: The fungus infected new locusts until the population crashed (compared to the repeated applications required by chemical pesticides).

Still, the problem is one of costs. Biopesticides may be cheaper overall, but the cost the farmer sees is the price on the bottle. There, chemicals have an edge: the Green Muscle application cost $17 per hectare compared to $12 for conventional chemicals. Much of the cost was in the production of the fungal spores themselves.

Now researchers have discovered a technique to radically change that equation. A new approach developed by U.S. Department of Agriculture scientists brews the biopesticide with “liquid-culture fermentation,” versus conventional methods using an expensive nitrogen source (typically derived from agricultural commodities like milk casein at $6 pound). The fermentation can use less expensive sources such as soybean flour or cottonseed meal at 30 to 50 cents a pound to produce the fungus.

The next step is commercialization. In the case of Green Muscle, “most of the project’s impact is still to be felt,” reports the UN’s Food and Agriculture Organization. More than 10 years after developing a useful product, the project will likely take another decade or more to become widely adopted. “This is because the eventual level of sales of Green Muscle depends on the correction of the market failure whereby the human and environmental health costs of spraying chemical pesticides are not charged to the purchaser,” says the report. Or perhaps just a cheaper product.