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News Article

Pollinators and yields increase in IPM watermelon fields

Conservation efforts enhance biodiversity of natural enemies and wild bees

Watermelons grown with lower rates of pesticide had more than double the number of pollinator visits and produced higher yields than conventionally grown watermelons treated with fixed prescheduled pesticide applications in US Midwest states.

Four-year trials were carried out in fields in Indiana, a major watermelon-producing state, and other Midwest states, comparing the effects of integrated pest management (IPM) and conventional pest management on bee populations and yields. The IPM system relied on weekly scouting of pests followed by pesticide application only when pests reached predetermined threshold levels for economic damage. Below these levels, no pesticide was applied. Conventional pest management involved regular prescheduled pesticide application, regardless of pest intensity.

The field trial sites grew both corn, which is wind-pollinated, and watermelon, which is insect-pollinated, to replicate a real agricultural ecosystem in Indiana where watermelon crops are often grown in the middle of corn fields. Each site had a pair of 15-acre fields, one with untreated seed and using IPM, and the other using pesticide-treated seed and conventional pest management practices including regular insecticide sprays. The crops were rotated over the course of the study, and the impact of different soil types and environmental conditions at the different locations were examined.

Minimizing pesticide application had a measurable effect on biodiversity of non-pest species. Natural enemies, including wasps and ladybugs, increased in the low pesticide fields, and were almost certainly associated with keeping pest levels low. There was a noticeable increase in bee pollinators and in flower visits by bees in IPM fields. Visits from honeybees from colonies in fairly close proximity to the watermelon fields were similar but there was a marked increase in visits from native, wild bees. Despite having to travel at least 100 feet to reach the watermelon flowers, wild pollinators made up 80% of the flower visits while honeybees were only 20% even though their colonies were placed within a few feet of the watermelon field. Wild bee species identified included Melissodes sp., green sweat bee (including Agapostemon sp. and unrelated taxa in the tribe Augochlorine), grey sweat bee (Halictus and Lasioglossum sp.) and squash bee (Peponapis pruinosa).

Pests rarely reached threshold levels and the number of pesticide applications was 95% less in the IPM fields than the conventional fields (97 vs 4 treatments)

Watermelon yields were 26% higher in IPM fields than in conventional fields. Corn yields showed an upward trend in IPM fields but there was no statistical difference between yields in IPM and conventional fields.


Pecenka, J. R.; Ingwell, L. L.; Foster, R. E.; Krupke, C. H.; Kaplan, I. IPM reduces insecticide applications by 95% while maintaining or enhancing crop yields through wild pollinator conservation. PNAS (2021) 118 (44) e2108429118



Article details

  • Author(s)
  • Alexis Rendell-Dunn
  • Date
  • 30 November 2021
  • Subject(s)
  • Tropical & subtropical fruits