Both commercial bees and wild pollinators do much better on farms that use synthetic pesticides sparingly, according to a three-year study on US farmland.
at Purdue University, Indiana, and his colleagues placed colonies of commercial honey bees (Apis mellifera) and bumblebees (Bombus impatiens) in fields of watermelon surrounded by corn, and collected pollinators visiting watermelon flowers.
At each site, they compared two fields with different pest management regimes. The conventional approach used corn seed coated in thiamethoxam, a widely used neonicotinoid pesticide, while watermelon plots were drenched with imidacloprid, another neonicotinoid, and crops were sprayed with a quick-acting insecticide at intervals during their growing season.
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The second approach, called integrated pest management (IPM), didn鈥檛 use the seed coatings or soil drench, and sprays were only used when weekly checks showed that a pest called the striped cucumber beetle (Acalymma vittatum) had exceeded levels of five individuals per plant 鈥� a threshold only reached four times over the course of the study.
Compared with conventionally managed fields, honey bee hives in IPM fields were heavier, suggesting higher pollen and nectar collection. They also had greater numbers of workers and more survived the winter. Bumblebees had larger colonies and greater numbers of eggs and larvae, as well as higher queen survival and larger nectar stores.
In conventional fields, 97 per cent of samples of bumblebee nest material contained at least one neonicotinoid pesticide, compared with 13 per cent in IPM areas. Significantly higher levels of neonicotinoid residues were found in honeybee colonies from conventional fields than IPM fields.
More than twice as many wild pollinators were collected in IPM fields, and they included more than twice as many species, among them the pure green sweat bee (Augochlora pura) and various other bees and hoverflies.
鈥淭here鈥檚 mounting evidence that if you reduce the number of hazards, bees are going to be doing a better job, but I think really quantifying how quickly the wild bee population responded was really striking,鈥� says Pecenka. 鈥淲e expected after repeated years of creating a safer environment we would start to see the effects, but these native and wild species of pollinators were homing in on the watermelon field right away.鈥�
In a based on the same experiment, Pecenka鈥檚 team found that watermelon yields rose by 26 per cent in the IPM fields due to improved pollination, while there was no negative effect on corn yield.
鈥淭he benefits to managed and wild pollinators are also likely to be reflected in other non-target groups of organisms, such as natural enemies of key crop pests,鈥� says at Harper Adams University, UK. 鈥淔urthermore, the economics of crop production are improved by avoiding unnecessary pesticide applications.鈥�
Scientific Reports
