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Booth, Samuel, W. (2023) Assessing the behaviour of wireworms in soil using non-destructive imaging techniques. PhD thesis, University of Nottingham.

PDF (Thesis with corrections from viva examination) (Thesis - as examined) - Repository staff only until 1 October 2025. Subsequently available to Anyone - Requires a PDF viewer such as GSview, Xpdf or Adobe Acrobat Reader Available under Licence Creative Commons Attribution. Download (16MB)

Abstract

Wireworms are the larval stage of click beetles, and some species are significant agricultural pests, causing stand reduction in cereal crops through consumption of freshly planted seeds and seedlings. Their management is difficult due to the long-lived nature of the larvae in soil, an ability to recover after intoxication, and restrictions on the use of previously effective compounds. Whilst much previous work exists on treatment efficacy in terms of ability to cause mortality, the sub-lethal effect on behaviour of these compounds has not been comprehensively studied. Understanding these sub-lethal effects alongside a treatments lethal effect to reduce population levels is vital in developing treatments that can effectively reduce yield losses. Studies of this kind are difficult due to the opaque nature of soil. X-ray Computed Tomography (CT) is a technique widely used across rhizosphere research as it is able to non-destructively image soil characteristics and root interactions in the soil.

X-ray CT has many benefits, as it is able to non-destructively image the internal structures of objects via X-ray attenuation, with denser components having higher attenuation. This can allow the visualisation and quantification of never observed structures before, which in turn can provide data on soil structure. X-ray CT has previously been used to observe the differences in pore structure between different agricultural management practices, as well as variation in root growth in response to differences in soil characteristics such as bulk density. For crop protection, this method has potential to observe pest response to treatments in situ, and determine non-lethal behavioural effects to different treatments.

Despite its many benefits, X-ray CT has a number of limitations, particularly in its use in the scanning of any sort of living system. The resolution of a scan is in part determined by the size of the object being scanned, which in the case of a growing plant, will quickly be outgrown and require re-potting and alternative scanning methodology. This limits the window that an X-ray CT study of wireworm behaviour is able to be conducted, and due to the ionising nature of radiation there may be negative effects to organism health due to X-ray exposure. As well as this X-ray CT scanning is expensive, both in system purchase, maintenance, data storage and time to process results.

Using X-ray CT, a non-invasive temporal study of wireworm behavioural response to crop species and insecticide treatments was conducted. Behaviour was primarily inferred from changes in burrow structures and compared to data obtained from traditional health assessment on treatment toxicity alongside infrared recordings to assess mechanisms. The first aim of this work was to assess if it was possible to image wireworm interactions with root structures in soil using X-ray CT, and then to refine this method ensuring it causes no negative health impacts to wireworms. The second aim was to determine wireworm response to insecticide treated seeds and use these data to compare efficacy of insecticide treatments for both lethal and sublethal effects, aiming to give a recommendation of the best treatment for the protection of maize and barley crops.

Results confirmed it is viable to image wireworm interactions with root structures in soil, with segmentation of roots, wireworms and burrow structures possible. Following method refinement, it was determined X-ray CT had no negative effects on the health of wireworms and is suitable for large scale study of wireworm behaviour. In response to different crop species, wireworms displayed different burrowing behaviour between maize and barley crops, producing a pore network of differing volume and complexities. This suggests behavioural differences in wireworms in response to crop species, possibly due to decreased searching behaviour in response to different root systems. For example maize roots are easier to orientate towards, producing smaller, shallower less complex burrow networks. Wireworms also produced different burrow structures in response to insecticide treated maize, with a plinazolin treatment eliciting larger, more complex burrow network formation compared to untreated maize. This may be due to increased searching due to aversion or a direct result of intoxication symptoms, but further work is needed to determine the mechanism behind this. This behaviour was not observed after exposure to any other insecticide treated maize, or any insecticide treated barley. Following health assessments after exposure, plinazolin, tefluthrin and thiamethoxam treatments all cause significant mortality compared to untreated maize, but only plinazolin and tefluthrin treatments did so compared to untreated barley. Whilst all maize treatments were able to cause significant mortality compared to control, and so are recommended for use in regard to managing wireworm populations, only plinazolin appeared to have significant sub-lethal behavioural effects on wireworms. This treatment may hold the key to better crop protection in the future, able to reduce populations with the potential to modify behaviour and reduce yield losses alongside it, but further work is needed to validate this and to observe the same effect in other crops. From infrared recorded choice experiments aversion as a mechanism remains inconclusive, but the method shows promise in the future alongside X-ray CT to elucidate the cryptic behaviour of wireworms. Combined these methods can not only observe behaviour of wireworms in response to stimuli but have the potential to determine mechanisms behind these behavioural displays. In terms of crop protection, the implications of this are unprecedented, with the ability to determine sublethal effects of a treatment in situ potentially allowing for the development of new chemical compounds able to act at more localised sites and with lower toxicity to the wider environment. Furthermore, with refinement, the methods developed in this thesis have application across a wide variety of soil invertebrate species, crops and different types of management strategies, allowing for new avenues of product development to be explored.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Mooney, Sacha Sturrock, Craig Kurtz, Benedikt de Heer, Martine
Keywords:	Wireworm, behaviour, X-ray CT, Soil, Pest, Insecticide, Imaging
Subjects:	Q Science > QL Zoology > QL605 Chordates. Vertebrates S Agriculture > S Agriculture (General)
Faculties/Schools:	UK Campuses > Faculty of Science > School of Biosciences
Item ID:	73146
Depositing User:	Booth, Samuel
Date Deposited:	22 Jul 2023 04:40
Last Modified:	22 Jul 2023 04:40
URI:	https://eprints.nottingham.ac.uk/id/eprint/73146

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