Using pesticides as needed brings in wild bees, increases watermelon yield without reducing corn profits


WEST LAFAYETTE, Ind. – Many farmers rent beehives to pollinate crops, but they could take advantage of the free labor of wild bees by adopting a pesticide-friendly approach, according to a new proof-of-concept study.

A multi-year study of commercial-scale fields in the Midwest found that this approach led to a 95% reduction in pesticide applications, while maintaining or increasing the yield of corn and watermelon crops. The results are detailed in an article published in the Proceedings of the National Academy of Sciences.

“An as-needed approach to pesticide treatment can benefit farmers,” said Ian Kaplan, professor of entomology at Purdue University, who led the project. “With reduced pesticide use, in the first year we saw wild bees returning to the fields, and our results showed an average 26% increase in watermelon yield. “

The Purdue Agricultural College research team studied fields in five different locations in Indiana and the Midwest over a four-year period to compare conventional pest management with an integrated pest management approach, or IPM. The IPM approach relied on scouting fields and applying pesticides only when pest levels reached pre-established thresholds for damage that would result in economic loss.

In recent decades, pesticides have been used preventively, starting with treated seeds and followed by applications according to a set schedule, said Christian Krupke, professor of entomology and member of the research team.

“More frequent use of these powerful insecticides increases the potential for unintended consequences and damage to insects, animals and human health. This study shows that we may not need such powerful weapons to fight parasites and, at a minimum, we don’t need to use them as often as we do, ”Krupke said.

Agricultural sustainability and the benefits of IPM are gaining attention. Walmart recently announced a policy requiring all global suppliers of fresh produce and flowers to adopt IPM practices by 2025.

“It’s important for people to know that there is another option between conventionally grown produce and organic produce,” said Kaplan, who heads the Purdue Insect Ecology Lab. “IPM can dramatically reduce the amount of pesticides used to grow food without completely removing the tool from farmers or endangering the food supply. “

Midwestern growers are also listening to the problem and want solutions to protect their crops and pollinators, said Laura Ingwell, assistant professor of entomology. Indiana is one of the top watermelon producing states in the United States, and pollinator-dependent cultivation averages 7,000 acres of land per year.

“Unfortunately, it is difficult to find untreated corn or soybean seeds,” she said. “Across the Midwest, watermelon fields are like islands in a sea of ​​corn and soybeans. We have to understand how managing one impacts the other, because many farmers in Indiana have all of these crops in rotation. “

The team worked with agricultural staff from Purdue’s research fields to grow both corn, which is wind pollinated, and watermelon, which is pollinated by insects, to replicate a true agricultural ecosystem in Indiana. Each site had a pair of 15-acre fields, one with untreated seed and using LAI, and the other using treated seed and conventional pest control practices like schedule-based insecticide sprays. Crops were rotated during the study, and the different locations allowed the team to examine the impact of different soil types and environmental conditions, said Jacob Pecenka, a graduate student who achieved great part of the study.

“We used weekly scouting to watch for parasites in the IPM fields, which means we would go out into the field, look for the parasites and take a sample of the number of different parasites present,” he said. “It was surprising that pests rarely reached the established threshold of economic risk to crops. Only four times during the study did the parasites reach a threshold that triggered the application of pesticides. This is a huge reduction compared to the 97 treatments of fields managed in a conventional way.

Pecenka and her team also monitored the flowers and counted the number of bee visits to the watermelon fields.

“IPM fields saw a 130% increase in the number of flower visits compared to conventional fields,” he said. “The biggest players in pollination were the native wild bees. They are efficient pollinators and serious foragers.

Due to the watermelon crops grown in the middle of cornfields, all wild pollinators had to travel at least 100 feet to reach the watermelon blossoms. Despite this challenge, wild pollinators made up 80% of flower visits while bees made up only 20%, even though their colonies were placed a few 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 resistant,” he said. “During the first year, these bees were very present in fields with low levels of pesticides, which can kill the bees, disrupt their navigation and repel them. “

The team also observed an increase in the number of beneficial insects in IPM fields, Ingwell said.

“Wasps, ladybugs, and other natural predators of watermelon pests come into play when parasite levels rise,” she said. “It’s tempting to pretreat with pesticides as an insurance policy for your crop, but this study shows that we can trust the natural system most of the time. Weekly scouting of the watermelon crop is sufficient to maintain yield and benefit the insect community in terms of pest control and pollination.

Resources for protecting pollinators and fruit and vegetable growers are available from the Purdue Extension offices.

The team, which also included Professor Emeritus Rick Foster, then plans to expand the study using 50-acre commercial fields.

US Department of Agriculture National Institute of Food and Agriculture (Grant n ° 2016-51181-25410) financed the works.

Writer: Elizabeth K. Gardner; 765-441-2024; [email protected]

Sources: Ian Kaplan, [email protected]

Christian Krupke, [email protected]

Laura Ingwell, [email protected]

Jacob Pecenka, [email protected]


IPM reduces insecticide applications by 95% while maintaining or improving crop yields through conservation of wild pollinators

Jacob R. Pecenka, Laura L. Ingwell, Rick E. Foster, Christian H. Krupke and Ian Kaplan

The study of pest management practices in modern industrial agriculture has increasingly relied on insurance-based insecticides such as seed treatments that are poorly correlated with pest density or damage to pests. cultures. This approach, combined with high invertebrate toxicity for newer products like neonicotinoids, makes it difficult to conserve beneficial insects and the services they provide. We used a four-year experiment using replicated commercial-scale fields at multiple sites in the US Midwest to assess the consequences of adopting integrated pest management (IPM) using pest thresholds against standard conventional management (CM). To do this, we used a systems approach that integrated the co-production of a regionally dominant row crop (maize) with a specialized crop dependent on pollinators (watermelon). Pest populations, pollination rates, crop yields and system profitability were measured. Despite higher pest densities and / or damage in both crops, pests managed by LAI rarely reached economic thresholds, which reduced insecticide use by 95% (97 vs. 4 treatments in CM and in IPM, respectively, across all sites, crops and years). In IPM corn, the lack of neonicotinoid seed treatment had no impact on yields, while IPM watermelon experienced a 129% increase in pollinator visit rate to flowers, resulting in 26% higher yields. The pollinator enhancement effect under IPM management was entirely mediated by wild bees; honey bee foraging was not affected by treatments and overall was not correlated with crop yield. This proof-of-concept experiment mimicking on-farm practices illustrates that cropping systems for major agricultural commodities can be redesigned through LAI to harness ecosystem services without compromising, and in some cases increasing, yields.

Connect: IPM Reduces Insecticide Applications by 95% While Maintaining or Improving Crop Yields Through Conservation of Wild Pollinators | PNAS

Agricultural communications: 765-494-8415;

Maureen Manier, Head of Department, [email protected]

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