It is becoming increasingly recognised that natural enemies in arable land, particularly polyphagous predators such as carabid beetles, may help to suppress populations of pests, and that appropriate management of such predators may lead to a satisfactory level of pest control. Previous work has shown that a polyphagous carabid predator, Pterostichus melanarius, is capable of affecting the spatial and temporal dynamics of slug pest populations. This project is an examination of how P. melanarius affects the survival, behaviour and dispersion of two important slug pests, Deroceras reticulatum and Arion intermedins, and how this information applies to spatial and temporal data previously obtained from the field. Deroceras reticulatum, but not Arion intermedius, elicited a variety of anti-predator behaviour in the presence of substrates previously exposed to the predator. The movements of slugs in arenas, incorporating a zone containing paper upon which the predatory beetles had previously been maintained and a control zone, were recorded at intervals. Significantly more slugs of all the size classes tested accumulated on the control half of arenas after 24 hours, with small slugs being quickest to respond. Slugs avoided paper exposed to both male and female beetles. Slugs also avoided paper exposed to another predatory carabid, Pterostichus madidus, but not to Harpalus affinis, a phytophagous carabid. Slugs did not respond to paper that had been exposed to beetles and then stored for five days prior to the test. Changes in parameters of movement of slugs when in the presence of P. melanarius chemicals were detected using a video-tracking system. These changes are consistent with a kinesis that would enable slugs to rapidly escape from areas where beetles were recently present. Despite this no changes in the rate of dispersion of D. reticulatum juveniles was detected in mini-plots previously exposed to P. melanarius. However, adult D. reticulatum reduced feeding and egg-laying and increased refuge on soil previously exposed to P. melanarius. Chemicals on the exterior of P. melanarius were isolated and two compounds were found to reduce feeding by D. reticulatum on leaf discs compared to control discs. One of these chemicals is currently being analysed using mass spectroscopy and NMR to determine it's structure and identity. It was concluded that D. reticulatum have evolved behavioural responses to chemical cues from either this generalist carabid predator in particular, or carabid beetles generally, many species of which include molluscs in their diets. During a video-tracking study of beetle movements, some evidence was found for the detection and response of beetles to slug mucus, and amputation work suggested that the palps may be important in slug detection. Previous feeding experience was found not to influence prey choice in P. melanarius during a food choice experiment, with beetles always selecting a mixed diet when offered. Analysis of spatial data showed that slug size, but not beetle sex, was important in the spatial relationship between the predator and the prey, and this agrees with results from the laboratory experiments of slug behaviour. This work has added to the evidence provided by other studies that some generalist predators can have significant effects on the dynamics of pest populations and therefore may become useful biocontrol agents for pests if effectively managed. The implications of this work in the field of predator-prey ecology and for the efficacy of P. melanarius as a biological control agent of slugs are discussed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:583648 |
| Date | January 2005 |
| Creators | Armsworth, Clare Gillian |
| Publisher | Cardiff University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://orca.cf.ac.uk/55967/ |
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