Birth control for bugs: controlling pests without pesticides

By Jenna Gallegos

March 8, 2018

Insects are a huge problem for agriculture — a multibillion-dollar, disease spreading, fat juicy larvae in your corncob kind of a problem. And while pesticides are pretty good at keeping weevils out of your breakfast cereal, they aren’t great for beneficial insects like butterflies and lady beetles.

What if, instead of killing bad bugs, we could stop them from making baby bugs? Scientists and farmers have been doing just that for over 50 years, using three main strategies for buggy birth control: radiation, hormone manipulation and genetic modification. Some of these strategies are considered organic and others are not. But the goal is the same: keeping crops free from pests while protecting beneficial bugs from pesticides.

Irradiation makes insect infertile

It all started with a really nasty bug called the screwworm. These flesh eating parasites screw and worm their way into animal or even human flesh. In the 1950s, the screwworm infestation got so bad it was costing livestock producers an estimated $20 million every year.

It turned out that the key to eradicating screwworms was not to kill them, but to release them.

In the early part of the 20th century, geneticist Hermann Muller started zapping bugs with x-rays. What Muller — one of the earliest purveyors of the dangers of radiation — eventually discovered was that irradiating fruit flies makes them infertile.

Screwworms grow up to be flies, so when other efforts to control the pest were failing, a group of USDA scientists decided to try Muller’s approach. They used radiation to sterilize male screwworms and released the infertile flies.

The mutant males competed for mates, so that fewer and fewer fly fertilizations resulted in baby worms. The technique was so effective, that screwworms were eradicated from the United States for 30 years until they returned, presumably re-introduced through one of the many means by which invasive species migrate.

Sterility by irradiation has since been used to control several important pests, including flies, moths and mosquitos on both organic and conventional farms.

Hormone traps prevent bugs from mating

Some insects, including several moths, don’t respond as well to the “sterile insect technique.” The irradiation messes them up so badly, the poor mutant moths can’t fly properly or attract a mate. Without sterile suitors to compete, farmers have to use another strategy: pheromones.

Pheromones are the sex hormones that help insects attract a mate. Scientists figured out the molecular structure of pheromones and synthesized copycats. The synthetic pheromones attract and confuse the male moths or lure them into traps, so they can’t mate.

A long list of insect pheromones has been developed. Unfortunately, pheromones aren’t always effective against particularly bad infestations. They can also be very expensive. And while irradiated insects are approved for organic farming, synthetic pheromones are not.

Genetically engineered insects: sterility without the side effects

In 2002, a company called Oxitec had an idea. What if, instead of zapping insects with radiation, we could specifically alter one gene that we knew would prevent live offspring?

Radiation introduces tons of unknown mutations that can prevent the sterile insects from mating effectively. Oxitec came up with a strategy for making targeted changes that would cause the engineered insect’s offspring to die. The company soon began testing what would become its most famous insect, the “self-limiting” mosquito.

With the goal of eliminating dengue, Oxitec released its male mosquitos in the Cayman Islands and in Brazil (only females feed on humans). The self-limiting males decreased the mosquito population by over 80 percent. The same species of mosquito that carries dengue also spreads zika. In 2016, voters approved the release of self-limiting mosquitos in a Florida suburb to combat zika.

Mosquitos have stolen the show, but Oxitec has applied its self-limiting technology to several pests, including the olive fly, two types of fruit fly and diamond-back cabbage moths.

Field trials with the self-limiting diamondback moth are currently underway at Cornell University. Should the technique prove effective, it is still uncertain how it will be regulated. While irradiated insects have had a green light for half a century, genetically engineered insects have faced much larger regulatory hurdles.

Public perception drives pest-control technologies

Though Florida voters approved the release of genetically engineered mosquitos, comments about field-testing engineered moths were far from positive. It seems counter-intuitive that voters would approve the release of mosquitos in their own backyard, but many strongly oppose the Cornell moth study.

The public perception of risks versus benefits for the two engineered bugs is very different. Mosquitos carry an immediate threat: zika. It is much more difficult to appreciate the ability of agricultural pests to threaten our supply of affordable food. But the diamond-back moth alone is estimated to cost farmers $4-5 billion every year. According to USDA data on food spending, that’s enough to feed over one million American households.

No one method of pest control is perfect, or applicable in every instance. Self-limiting technology offers another important option as farmers and public health officials struggle to deal with the insects that feast on our food supply and spread disease.