New understanding of ‘sociable’ slug behaviour calls for better pesticide targeting

Experts from the University of Leicester have been hot on the slime trail of the grey field slug population thanks to innovative technology that can tag and track the behaviour of the invertebrates.

In an interdisciplinary study led by Professor Sergei Petrovskii, a team consisting of biologists and mathematicians injected unharmful radio-tags (about the size of a grain of rice) into 28 slugs, released them into a crop-growing field and radio-tracked them for ten hours, recording their behaviour.

The collected data, analysed using the mathematical technique known as the ‘correlated random walk’, found that slugs enjoy congregating in ‘high density patches’, as opposed to spreading out across a field, making the case stronger than ever for targeted treatment of this major crop pest.

Professor Petrovskii explains: “Slugs are common pests that cause considerable damage to agricultural crops on an industrial scale as well as being a nuisance to gardeners. It is understandable to want to try and rid crops and plants of them.

“To date, the lowest-cost chemical option has been metaldehyde-based slug pellets. This chemical has dominated the molluscicide control scene and remains on the market but is due to be withdrawn in 2022 because of its unfriendliness to wildlife. 

“Our research showing the sociability of the slug population is crucial to help in the campaign for better pesticide targeting. There is no question in light of our findings that targeted treatment of the most mollusc-riddled parts of a field, as opposed to the blanket treatment, is the most friendly and effective method of pest control.”

Professor Petrovskii believes the pest control industry needs to look more closely at other options, including ferric phosphate and biological control and not wait until 2022 to do so.

Past research has shown slugs respond to metaldehyde-treated crops by producing lots of slime before dying on the soil surface whereas those treated with ferric phosphate stop producing slime, retreat underground and die a few days later. Alternative options to metaldehyde are associated with significantly higher treatment costs, so there is some reluctance among farmers and gardeners to adopt the friendlier pesticide methods.

Professor Ivan Tyukin who is a Research Director of the School of Mathematics and Actuarial Science at the University of Leicester says: “We hope that this research prompts farmers and gardeners and the broader society to consider more targeted approaches to pest control. We all need to play our part at every level to build a cleaner and greener Britain.”

The paper was published today in Scientific Reports.

• Movement patterns of the grey field slug (Deroceras reticulatum) in an arable field, DOI:10.1038/s41598-020-74643-3