Researchers work with beneficial insects and ecological balance to make growing pesticide-free strawberries attainable for farmers.

Fresh, local strawberries are a juicy treat on a summer day, warm from the sun out of a quart box. But it’s tough to grow those flawless berries without frequent applications of chemicals to stop insect pests and fungus, and strawberries are found at the very top of “dirty dozen” lists for high pesticide residues. In 2016, the last year the USDA chose strawberries for monitoring, they found traces of 36 different pesticides, acaricides and fungicides, more than on any other product. This gives extra incentive to producers to grow strawberries organically: the public wants them, and it means a big decrease in pesticide exposure for farmers and farm workers. Yet, only about 2.5% of strawberry acres in Canada are organic.

One of the insects driving high pesticide use on non-organic strawberries is the tarnished plant bug, or Lygus bug, Lygus lineolaris. This bug, described as a “strawberry menace” by University of Wisconsin Extension, causes deformed fruit and if left uncontrolled, can result in complete crop loss. The conventional way to manage the pest is to spray pesticides when tarnished plant bugs are detected at a certain rate in the strawberry field, and to keep the field clean of weeds or cover crops that would harbour the pests. This can mean up to 15 insecticide sprays in a single season. It also means a sterile system where most living things other than strawberry plants are considered a threat.

Enter our hero, the common damsel bug, Nabis americoferus. This bug is a predator native to North America, and it may be the key that unlocks a self-balancing pest control system, making organic strawberries a more viable option for farmers.

The damsel bug may be the hero, but we must also give credit to the research team at the Centre de recherche agroalimentaire de Mirabel (CRAM), a small but mighty research and extension institute in Quebec who recognized the bug’s potential.

CRAM scientist François Dumont made a spontaneous discovery of the insect’s voracious appetite for tarnished plant bugs in 2014. He says,

 « J’observais [le Nabis] aux champs, puis je l’ai pris dans ma main comme ça, j’ai traversé la rue qui est dans mon laboratoire, je l’ai mis dans une petite boîte de pétri avec une punaise terne pour voir ce que ça ferait. Puis, après 12 secondes, elle avait piqué la punaise terne dans l’œil, puis là, c’était comme wow que c’est ça ! »

« I observed [the damsel bug] in the field, and I took it in my hand… I crossed the road to my lab, I put it in a little Petri dish with a tarnished plant bug to see what it would do. After 12 seconds, [the damsel bug] stabbed the tarnished plant bug in the eye and it was like wow, so that’s what it does! »

Instead of the tight chemical control of a conventional strawberry field, the team at CRAM, including Drs Caroline Provost and François Dumont, recommend a system where the damsel bug keeps the tarnished plant bug under control. In this system, predator and pest live in balance at the margins of the field, on plants they actually like more than strawberries, and the tarnished plant bug does very minimal damage in the crop.

With this ecological balance, the system involves no insecticides at all: the sprays would kill both predator and pest, allowing the fast-breeding tarnished plant bug population to explode again. And it works. The research team measured a 75% reduction in strawberry losses when the damsel bug was introduced, and the tarnished plant bug population went down by half.

Only ten years after Dumont’s damsel bug detective work, over 50% of the organic strawberry growers in Quebec are now introducing it to their fields. Some farmers are newly transitioning to organic with the help of the damsel bug.

Farmers across Canada are likely to soon be able to purchase damsel bug eggs from the BC-based company Applied Bionomics, for use in strawberries and beyond. The tarnished plant bug is also a serious pest of peppers, eggplant, and celery, both in the field and in the greenhouse.