Not all predators are other bugs. Rachael Long has studied bats and their role in pest management in the Central Valley of California for 15 years. Pear, walnut and apple orchardists were fighting the codling moth. By studying DNA in the undigested parts of bat waste, she found they did eat the moths and other insects, equal to their body weight each night.

The next phase, which took eight years, was to find out how to attract bats to bat houses. “The pups are born without hair,” Ms. Long says. “So you have to put them where they get morning sun, so they are warm in the morning, and shade in the afternoon, so it’s not too hot.”

There’s a huge demand for bats in farm country, she said. “They eat a ton of insects,” Ms. Long said. “They also eat cucumber beetles and stink bugs, which affect tomatoes.”

A bat house needs to be attached to a structure like a barn or a bridge, she says, and not mounted on a pole. Hawks will wait for young bats to come out of a house, if it’s not sheltered, Ms. Long says, and pick them off one by one.

Organic researchers are also studying the role of soil fertility in pest control. Some studies show nutrient-rich soil may enhance the plant’s immune system and increase natural resistance to insects and pests, or provide a home to natural enemies. Organic soil in potato fields that Dr. Crowder studied, for example, has higher levels of a fungus that kills potato beetle larva than conventional fields.

Cover cropping, planting grasses and legumes that fix nitrogen between cash crops, can make a tremendous difference in soil, according to studies by Dr. Brennan. “If we can get farmers to plant a cover crop every three years instead of every 10, we would be much further ahead” in soil fertility, he said. “There’s a huge difference.”

Organic farmers aren’t averse to rolling out certain kinds of chemical sprays. Some  the so-called killer spices  are made from a blend of essential oils and water from strong-smelling plants like clove, mint and thyme. A decade of studies in Canada show that they can be very effective at repelling and killing pests, and are safe, though they aren’t active in the environment long and require multiple applications.