Reduced pesticides can lead to an increase in bee visits
Reducing the use of pesticides increases the number of bees visiting plants, which American scientists have found that boosts production.
A team of researchers from Purdue University found that using pesticides as needed increased wild bee pollination and watermelon yield.
A multi-year study of commercial fields in the American Midwest found this approach resulted in a 95 percent reduction in pesticide use while maintaining or increasing corn and watermelon crops.
The results are detailed in a paper published in the Proceedings of the National Academy of Sciences.
“A needs-based approach to pesticide treatment can benefit farmers,” said Ian Kaplan, professor of entomology at Purdue University, who led the project.
“With reduced pesticide use, we saw wild bees return to the fields within the first year, and our results showed an average increase in watermelon yield of 26 percent.”
The Purdue College of Agriculture team of researchers studied fields in five different locations in Indiana and the Midwest over a period of four years to compare conventional pest management with an integrated pest management (IPM) approach.
The IPM approach relied on exploring the fields and applying pesticides only when pest exposure reached pre-established thresholds for damage that would lead to economic loss.
In the past few decades, pesticides have been used preventively, starting with treated seeds, followed by applications according to a set schedule, said Christian Krupke, professor of entomology and member of the research team.
“The more frequent use of these potent insecticides increases the potential for unintended consequences and harm to insects, animals and human health,” he said.
“This study shows that we may not need such powerful weapons to fight pests, and at least not use them as often as we do.”
Prof. Kaplan, who heads Purdue’s Insect Ecology Lab, added, “It is important that people know that there is another option between conventionally grown produce and organic produce.
“IPM can significantly reduce the amount of pesticides used to grow food without completely depriving farmers of tools or endangering food supplies.”
Farmers in the Midwest are also prepared for the problem and want solutions to protect their crops and their pollinators, said Laura Ingwell, assistant professor of entomology.
Indiana is one of the largest watermelon growing states in the United States, and the pollination-dependent harvest averages 7,000 acres of land annually.
“Unfortunately, it’s hard to find untreated corn or soybean seeds,” she said. “Over the Midwest, watermelon fields lie like islands in a sea of corn and soybeans.
“We need to understand how cultivating one affects the other, as a lot of Indiana farmers have all of these crops in rotation.”
The team worked with farm staff in the Purdue research fields to grow both wind-pollinated corn and insect-pollinated watermelon to recreate a true Indiana agricultural ecosystem.
Each site had two 15-acre fields, one with untreated seeds and IPM, and the other with treated seeds and traditional pest control methods such as calendar-based insecticide sprays.
The crops were grown in turns over the course of the study, and the different locations allowed the team to study the effects of different soil types and environmental conditions, said Jacob Pecenka, a doctoral student who conducted much of the study.
“We used weekly scouting to monitor pests in the IPM fields.
“It was surprising that the pests rarely reached the set threshold for economic risk to the plants.
“Only four times during the study did pests reach a threshold that triggered the use of pesticides.
“That is an enormous reduction compared to the 97 treatments on conventionally farmed fields.”
Pecenka and his team also monitored the flowers and counted the visits from bees to the watermelon fields.
“The IPM fields had a 130 percent increase in flower visits over the conventional fields,” he said.
“The biggest players in pollination were native wild bees. They are efficient pollinators and serious collectors. “
Since watermelons were grown in the middle of the corn fields, wild pollinators had to travel at least 30 meters to get to the watermelon flowers.
Despite this challenge, wild pollinators made up 80 percent of flower visits, while honey bees made up just 20 percent, despite their colonies being just feet from the watermelon field, Pecenka said.
“We don’t have a great understanding of the biology of many wild bee species, but this study suggests that they are important and resilient,” he said.
“In the first year these bees were a significant presence in the fields with low pesticide concentrations that kill the bees, confuse their navigation and can repel them.”
The team also observed an increase in the number of beneficial insects in the IPM fields.