Air pollution threatens natural pest control methods

Researchers from the University of Reading have discovered that controlling aphids with parasitic wasps is more difficult in polluted environments.

According to researchers from the University of Reading, when fields of oilseed rape are exposed to air pollution from diesel-burning vehicles and industry, the number of parasitic insects available to control aphids significantly drops. This discovery is crucial, as scientists need to ensure sustainable food security now and in the future.

The research, titled ‘Concurrent anthropogenic air pollutants enhance recruitment of a specialist parasitoid,’ was published today in the journal Proceedings of the Royal Society B Biological Sciences.

Measuring how parasitic wasps respond to air pollution

The team of scientists used special equipment to supply controlled amounts of diesel exhaust and ozone to oilseed rape plants. Aphids were also added to the plants. The researchers then measured the reproductive success of parasitic wasps that habitually lay their eggs inside a freshly stung aphid.

Dr James Ryalls from the University of Reading’s department of Sustainable Land Management said: “Even at the levels we used, which were lower than safe maximums set by environmental regulators, the overall numbers of parasitic insects still fell. This is a worrying result as many sustainable farming practices rely on natural pest control to keep aphids and other unwelcome creatures away from valuable crops.

“Diesel and ozone appear to make it more difficult for the wasps to find aphids to prey upon and so the wasp population would drop over time.”

Studying whole systems is crucial for predicting and mitigating air pollutants

Although the majority of parasitic wasp species decreased in polluted environments, the researchers discovered that one species of parasitic wasp seemed to do better when air pollution was present. However, the team explained that when both diesel and ozone were present, this combination also correlated with other changes in the plants.

© iStock/Zoya2222

When the pollutants are both present, the researchers found that oilseed rape plants produced more of the compounds that give brassica family crops, such as mustards and cabbages, their distinctive hot and peppery flavour notes. Usually, these repel insects, but Diaretiella rapae wasps were instead found in greater abundance and were discovered to have reproductive success associated with diesel exhaust and ozone together.

Dr Ryalls said: “Diaretiella rapae particularly likes to prey on cabbage aphids, which love to eat brassica crops.

“We know that some of the flavour and smell compounds in oilseed rape are converted into substances that do attract D.rapae. So, we could speculate that the stronger smell attracts the wasps, and they are more successful in finding and preying upon aphids, that way. It could be that D.rapae is a good choice for pest control in diesel and ozone polluted areas.

“This really goes to show that the only way to predict and mitigate the impacts of air pollutants is to study whole systems.”

Future changes to air pollution need to be monitored

As the world shifts toward electrified transport, air pollution is expected to change, and it is important to know how pest-regulation service providers, such as parasitic wasps, respond to these progressive changes. Understanding the changes in response is essential for scientists to plan mitigation strategies, ensuring sustainable food security.

The research highlights the importance of monitoring the impact of air pollution on the plants, wasps, and prey insects, and the interactions between all three.

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