Examining potential biological and bio-rational control strategies for slugs

CHAP’s Dr Archita Barua and Dr Jenna Ross have collaborated with Dr Christopher Williams from Liverpool John Moores University, to publish a peer-reviewed paper in a special edition of the international journal ‘Insects’. Here, Archita and Jenna summarise their work and consider the implications for UK agriculture.

Our paper A Literature Review of Biological and Bio-Rational Control Strategies for Slugs: Current Research and Future Prospects, reviews non-chemical slug control strategies.

Slugs constitute a serious menace to agricultural production, resulting in significant economic damage to a wide range of crops, including oilseed rape, vegetables, legumes, cereals and fruits. Their ability to survive in unfavourable conditions, combined with their hermaphroditic nature, make them successful organisms that can be found almost everywhere.

Slugs are a pest on a global level, but in the UK the concern lies in that of the 42 slug species currently present, more than half are non-native and have successfully established populations. A recent study by AHDB concluded that the failure to control slugs could cost the UK agriculture industry in excess of £100 million annually.

Slug control measures

To reduce the risk of crop damage by slug pests, different control measures are available as a part of an integrated pest management programme. Current slug control strategies around the globe mainly rely on the use of chemical molluscicides containing methiocarb or metaldehyde as an active ingredient. However, there have been concerns over metaldehyde due to its impact on non-target organisms and water systems. Recently, the Department for Environment, Food and Rural Affairs (Defra) announced that the outdoor use of metaldehyde would be banned from March 2022, in the interest of the environment, to align with the 25 Year Environmental Plan and Environmental Bill in the UK, and to fulfil the sustainable development goals and for wider food security. In addition, methiocarb is now banned for use in the UK.

Therefore, it is increasingly important to find alternative, effective and environmentally benign slug control measures such as biological (i.e. using one living organism to control another) and bio-rational (i.e. controlling pests using products derived from natural sources) controls.

There are a variety of predators and parasites of slugs, but only a few have attracted biocontrol research interest. In parallel, several bio-rational control measures have been found to be effective in slug control, including, but not limited to, the use of essential oils (such as garlic oil and spearmint oil), plant extracts and caffeine.

This paper reviews the slug control potential of the three biocontrol mechanisms, namely nematodes, carabid beetles and sciomyzid flies, along with various bio-rational control strategies that have been studied by scientists to date. In doing so, this study also draws attention to the limitations of current research and discusses some important future research avenues in order to develop effective non-chemical slug control measures.

The way forward

Dr Barua said: “While some of the biological and biocontrol techniques discussed have tremendous slug control potential, they alone cannot reduce slug infestations significantly. Biological techniques should be supported by other mechanisms, such as advanced technology-driven tools. The traditional slug control process first involves the manual monitoring and identification of slugs and subsequent application of chemical/biological control techniques based on identified slugs.

“However, manual pest identification or monitoring is very time-consuming, inefficient, and labour-intensive. In the case of slugs, it is more challenging as they tend to avoid sunlight and feed at night. Therefore, we must consider other systems.”

Dr Jenna Ross added: “Slugs are major economic pests that target a wide range of agricultural and horticultural crops across the world. However, with an ever-limiting chemical toolbox, it is important, now more than ever, that research focuses on all areas of integrated pest management. Our publication gives a detailed overview of current research and future prospects of three key biocontrol mechanisms – nematodes, carabid beetles and sciomyzid flies, along with various bio-rational control strategies. The hope is that this publication will springboard potential R&D and collaborative opportunities, and we would encourage anyone with an interest in this field to get in contact.”

SlugBot

This publication stemmed out of a current CHAP-led Innovate UK funded project called SlugBot.  The SlugBot team have been working to develop an autonomous slug monitoring system that can be combined with precision application of biocontrol agents. The project is in collaboration with Small Robot Company (SRC) and farming enterprise AV and N Lee, which upon development, will the first of its kind in the world. SlugBot successfully combines CHAP’s expertise in malacology, biocontrol and multispectral imaging, with SRC’s expertise in robotics and artificial intelligence (AI).

For more on multispectral imaging, check out the CHAP Phenotyping Lab at Rothamsted Research, or watch our Phenotyping Webinar on YouTube.
If you are interested in working with us in the area of biological and bio-rational control strategies for slugs, please send us an email using the enquiries form at the bottom of our homepage.

Please note, the opinions expressed in this article are the author’s own and do not necessarily reflect the views or opinions of CHAP.