Imogen Poyntz-Wright, Online Science Editor, discusses the UK government allowing the use of emergency pesticide over fields and its effect on the environment.

In March 2022, the UK government allowed the emergency use of the pesticide thiamethoxam on sugar beet seeds to deal with the beet yellow virus. The virus is transmitted by an aphid (Myzus persicae, Aphis craccivora). Thiamethoxam is designed to kill aphids (insects) and therefore prevent the insect passing on the yellow virus to the sugar beet crops, protecting the plants and therefore crop yield.

Thiamethoxam results in the nervous system being disrupted resulting in paralysis and ultimately death

The pesticide in question is part of a larger family called neonicotinoids. Pesticides in this group share the same target site by which they cause the death of the insect/ pest. The target site for thiamethoxam is the neuronal nicotinic acetylcholine receptors, the chemical binds to this receptor acting as an agonist, causing the receptor to remain ‘excited’. This results in the nervous system being disrupted resulting in paralysis and ultimately death. Importantly the neuronal nicotinic acetylcholine receptors play an essential role with regards to neurotransmission, learning and memory processes, and even neurodegenerative diseases.

The emergency allowance could impact bee populations, but short-term use should mean populations can recover

Bees are exposed to thiamethoxam through pollen and nectar. Bees contain the same homologous molecular site, nicotinic acetylcholine receptors, as those of found in the target species, aphids. Thiamethoxam, therefore, targets the same receptor in bees which results in, according to laboratory studies, impaired locomotion, hyperactivity, impaired motor functions and impaired bee ability to ascend. This could reduce the health of colonies by harming worker locomotion in the field and result in population level consequences – that is, a decline in bee abundance as food acquisition through foraging activities is affected. The field evidence of this is patchy. Hence, the extent of which thiamethoxam affects bee populations is not certain, but what is certain is the chemical can have a negative impact on bees, an essential species for the pollination of crops. This emergency allowance of thiamethoxam, although needed to prevent crop loss from the yellow virus, could impact bee populations but the short-term use should mean that populations of bees, if affected, can recover. The problem arises if this emergency use becomes a yearly allowance.