Agriculture and climate change halve insect numbers

Climate change is already applying pressure on world insect populations – now scientists have found that in combination with intensive agriculture that pressure has caused insect numbers to drop by almost half.

Researchers from the University College London (UK) used the Natural History Museum London’s PREDICTS (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems) database to look at how over 17,000 species of insects, across more than 6,000 locations were being impacted by climate change and agricultural impact over a period of 20 years.

Location of PREDICTS sites that include insect data. Modified from Outhwaite, Nature 2022

They found that areas with combined high-intensity agriculture, and substantial climate warming, that the number of insects (abundance) was 49% lower, and number of different species (richness) was 29% lower, compared to natural habitats with no climate warming recorded. Tropical areas in particular saw the biggest declines in insect biodiversity linked to land use and climate change.

High-intensity agriculture is typically characterised by chemical input, low crop diversity, large field size and high livestock density. When comparing levels of agricultural intensity, high-intensity areas saw a reduction in 45% abundance, and 33% richness, while in low-intensity areas, this was a 19% reduction in abundance, and 22% in richness, showing just how much difference agriculture intensity can have on retaining insect biodiversity.

The authors of this research predict this loss of insect biodiversity will reduce ecosystem services essential to the agriculture industry, especially pest control and pollination, as well as reduce the resilience of the agricultural ecosystem to future climatic events.

Response of insect total abundance (a) and species richness (b) to interaction between land use and standardized temperature anomaly. Credit: Outhwaite, Nature 2022

“In areas with high-intensity agriculture, there is usually a low diversity of plants. While pollinators feed on crops while they are in flower, after harvest if there is no diversity of crops in the area, there won’t be any food sources for the insects to sustain their population until the next season.” explains Dr Katja Hogendoorn, senior researcher of bees as pollinators of crops and native plants, at the School of Agriculture, Food and Wine at the University of Adelaide.

The findings of this study also demonstrate the importance of having large and diverse natural habitats adjacent to agricultural land to ensure insects are not dependent on a single seasonal crop species. In areas of low-level agricultural intensity, with high levels of natural cover available (75% cover), abundance is reduced by only 7% and richness by 5%, compared to 63% and 61% in places with lower levels of natural habitat (25% cover).

“Eucalypts support many native and commercialised honey bee species, but with climate change bringing on greater drought events, even though flowers are being produced, little nectar is being provided. Having a diversity of plants, having smaller crop fields and maintaining nature strips will provide alternative food sources to beneficial insect communities in and around crops.” Dr Hogendoorn emphasises.

These results show that insect biodiversity will likely benefit from mitigating climate change, preserving natural habitat within landscapes and reducing the intensity of agriculture.

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