On the horizon: omega-3 fatty acids in oil crops – saving fish or threatening insects?

An emerging genetic technology that makes oilseed crops produce omega-3 fatty acids promises health and sustainability benefits, but there’s a potential adverse impact on insects that hardly anyone is talking about. Lynn Dicks and Xavier Le Roux round off our ‘On the horizon’ series.

Polyunsaturated, long chain omega-3 fatty acids are the reason why healthy diet recommendations usually include seafood and oily fish like salmon, anchovy or herring. Fishy omega-3s have long been thought to have health benefits, particularly for the heart*. Most land plants don’t produce them, and so land animals are not exposed to them much unless they eat food from aquatic sources, such as fish or aquatic insects.

These long chain omega-3 fatty acids are a nutritional requirement for fish and other marine and freshwater vertebrates. The salmon-farming industry buys fishmeal in large quantities, because omega-3s would be largely missing from alternative land-based sources of protein that might be more sustainable as fish food. Fishmeal, which often comes from harvests of smaller fish such as anchovies, is also sold for use in human dietary supplements, again, for its omega-3 content.

There is a catch – ‘cabbage white butterflies reared on diets containing the two ‘fish oil’ fatty acids engineered into transgenic plants have heavier bodies, smaller wings and a greater risk of wing deformity’

Genetically engineering oil crops to produce long-chain omega-3s might, therefore, seem an attractive prospect. It increases the human health benefits of the oil and it offers a route to reducing the harvest of small wild fish to feed the aquaculture industry. Given these benefits, if the transgenic oilseeds currently being developed pass regulatory trials, they could soon be widely grown around the world.

Here’s the catch. Research has shown that when omega-3s (specifically eicosapentaenoic acid and docosahexanoic acid) are introduced into land plants, the proportion of a shorter chain omega-3 fatty acid – alpha-linolenic acid – is reduced by at least half. And that one is essential to healthy growth and development of land-dwelling insects, like butterflies and bees. Cabbage white butterflies reared on diets containing the two ‘fish oil’ fatty acids engineered into transgenic plants have heavier bodies, smaller wings and a greater risk of wing deformity than those fed on normal diets. In another study, bees fed on a diet poor in alpha-linolenic acid were shown to have lower learning abilities [7]. If replicated in the wider environment, such changes would negatively impact feeding success and dispersal, potentially leading to population-level impacts on insects.

In contrast, research on aquatic invertebrates such as copepods and mussels has shown that omega-3s stimulate their growth and reproduction. An effect like this on land-dwelling insects could intensify agricultural pest problems.

So, come on entomologists! Go out and research the impacts of genetically-engineered oil crops on insect development, growth, behaviour and reproductive success. Whatever your results show, don’t forget to share your findings with the world. Crop breeders, agricultural advisors, regulators and farmers all need to know what the research shows when they consider whether or not to use, or develop, omega-3 enhanced oil crops.

*Recent medical research does not actually support this very strongly, but people buy them as food supplements anyway 

A Horizon Scan of Emerging Issues for Global Conservation in 2019 is available to read in Trends in Ecology and Evolution.

Read more from our ‘On the horizon’ series here:

Introduction  by Bill Sutherland and Nancy Ockendon

Climate change and the capacity of Antarctic benthos to store carbon by Nathalie Pettorelli

Deforestation expansion of plantations and infrastructure threaten Indo-Malay island species by Nafeesa Esmail and Alice Hughes

Options for cultivating rice as climate changes and salinity increases by Erica Fleishman

Plastic alternatives – the ecological impact is not always clear by Becky LeAnstey

Mercury rising by Colleen Seymour

Food for the future – regulating gene-edited plants by Helen Doran

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