January 13, 2021, by Andrew Edwards (Ed)

Bees and neonicotinoids – what does the science say? – by Prof. David E. Salt

Photo by Roberto Patti on Unsplash

DEFRA has announced that, for the 2021 growing season, thiamethoxam will be allowed to treat sugar beet seeds, prior to planting. This is a temporary authorisation for 2021 only but may be extended for the 2022 & 2023 growing seasons. This has understandably caused controversy and elicited passionate reactions.

Thiamethoxam is one of a class of pesticides called neonicotinoids, intended to kill insects that feed on farmers crops. Neonicotinoids are therefore very toxic to insects and this includes beneficial insects such as bees. Fortunately, thiamethoxam has much lower toxicity to mammals, fish and birds, and no toxicity to plants because plants lack a nervous system, which these compounds target.

In 2012, routes for bees to be exposed to these compounds via dust, pollen and nectar were identified. The compounds were found to persist in agricultural irrigation channels and soil. This eventually led to the EU (which then included the UK) banning the 3 main neonicotinoids (clothianidin, imidacloprid and thiamethoxam) for all outdoor uses.

The neonicotinoid seed treatment recently temporarily authorised for use on sugar beet provides protection against aphids and the damaging viruses they can transmit to the plants. This protection has been requested by farmers due to an ongoing outbreak in the sugar beet crop of ‘beet yellows virus’, which is actually a set of 3 different viruses, transmitted by aphids. This outbreak is causing significant reductions in sugar beet yields.

Here are some important points to consider as you evaluate the evidence to determine whether this decision by DEFRA of this limited authorisation of the use of thiamethoxam appropriately balances the risks and benefits:

1. The compound will not be sprayed on the plants growing in the fields but rather used to treat seeds. This limits exposure to bees.

2. Sugar beet as a crop is harvested before it flowers so bees are not attracted to the plants. Again, this limits bee exposure.

3. The compound could get into other flowering plants around the edges of the fields and expose bees. It is planned that these flowering plants will be removed.

4. The compound can remain in the soil and get into flowering crops next season (e.g. rapeseed). To avoid this, flowering crops will be excluded from the fields where thiamethoxam has been used for 2 – 3 seasons, by which time the compound will have degraded in the soil.

5. Sugar beet cultivation in the UK is spatially restricted to the east of England, located around 1 – 4 beet processing factories. This makes the control measures recommended above more tractable to implement, monitor and enforce.

6. These usage requirements should only be temporary (2021 – 2023) because longer term strategies that do not require neonicotinoids are under development, including

   • development of plant varieties resistant to the virus

   • new agricultural practices for farmers to limit the spread of the virus

Clearly, neonicotinoids are toxic to bees; that is bad and their use needs to stop. We need to ensure that:

1. Short term action (next 1 – 3 years) – The safety practices included in the current authorisation (e.g. removing flowering weeds, not planting flowering crops for 2-3 years) are adhered to by the farmers, and this temporary authorisation for use on sugar beet is not extended beyond 2023;

2. Mid term approach – Sustainable approaches to sugar beet cultivation are delivered through research and its application to eliminate the need for chemical control of pests.

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