title / Development of repellents against vertebrate pests with special
reference to rabbits, badgers and grey squirrels / DEFRA
project code / VC0414
Department for Environment, Food and Rural Affairs CSG 15
Research and Development
Final Project Report
(Not to be used for LINK projects)
Two hard copies of this form should be returned to:Research Policy and International Division, Final Reports Unit
DEFRA, Area 301
Cromwell House, Dean Stanley Street, London, SW1P 3JH.
An electronic version should be e-mailed to
Project title / Development of repellents against vertebrate pests with special
reference to rabbits, badgers and grey squirrels
DEFRA project code / VC0414
Contractor organisation and location / Central Science Laboratory
Sand Hutton
York
Total DEFRA project costs / £ 385,600
Project start date / 01/11/98 / Project end date / 31/03/02
Executive summary (maximum 2 sides A4)
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CSG 15 (9/01) 3
Projecttitle / Development of repellents against vertebrate pests with special
reference to rabbits, badgers and grey squirrels / DEFRA
project code / VC0414
1. Repellents offer the prospect of humane, effective and environmentally sensitive alternatives to traditional wildlife management methods involving lethal control. In order to exploit this potential a collaborative research programme, integrating expertise within the Central Science Laboratory (CSL) and the Wildlife Conservation Research Unit University of Oxford (WildCRU), sought to identify, develop and test humane and cost-effective repellents for use against rabbits, badgers and grey squirrels based on a sound understanding of the underlying biological principles. This report describes the development of three approaches to resolving conflicts between problem wildlife and humans: application of plant defence compound precursors to systemically enhance crop resistance to rabbit damage, the use of multi-sensory formulations as badger repellents and capsaicin as a grey squirrel repellent.
2. In the preceding project VC0404, the elevation of natural plant defence strategies was identified as an exciting new approach to reducing wildlife damage to crops. This can be achieved by the application of plant defence compound precursors that are taken up by the plant, converted into defence compounds and subsequently translocated throughout the plant tissues. Our specific goal was to boost the natural physical defences of wheat plants and thus reduce their palatability to rabbits. Wheat, like many grasses, has a number of physical defences to deter herbivores including leaf trichomes made of silica. Vertebrate herbivores actively discriminate between high and low silica grasses and preferentially feed on the latter. In VC0404 we showed that systemic application of soluble silicates successfully boosted the levels of silica in wheat plants, which in turn enhanced their resistance to rabbit damage (wheat was grown under hydroponic conditions with addition of sodium silicate solution). The objective of this project was to identify a practical and cost-effective method of boosting silica levels of wheat. Silicate (slag) fertilization was identified as being potentially a cost-effective method, as this technique is already an established agronomic method for increasing plant development, growth and yield.
3. Four granular sources of silicates were tested for their potential to boost silica levels in wheat. Plants grown in soil with added phosphorus furnace slag (PFS) and Sipernat 880 (at application rates of 1 tonne Si per hectare) had twice the silica levels of control plants. It was encouraging to find that silicate treatment was effective at elevating silica levels in a range of wheat varieties. Also encouraging was the fact that there was an increase in young plant growth (a maximum increase of 22 % dry plant weight) when PFS and Sipernat were added at 1 t/ha. However, this was not reflected in an increase in yield of greenhouse-grown plants. Silica fertilization has been known to increase resistance of some crops to insect and fungal attack. We found that wheat grown in soil with added silicates (1 t Si/ha) was more resistant to mildew than control plants. Control plants had 2.8 and 3.8 times the area infected with mildew than silicate-treated plants when assessed 2 and 3 weeks following inoculation respectively.
4. To assess whether or not this systemic approach could also benefit dicotyledonous crops, we evaluated the effects of silicate treatment on oilseed rape. We found that although there were elevated silica levels at silicate applications of 0.5 and 1 t Si/ha (1.5 and 2.6 times control levels respectively), there was a detrimental effect on young plant growth at 1 t Si /ha. Thus a lower application rate is recommended for this crop. We found no evidence to suggest that the silicate treatment had any significant effect on the production of phenolic defence compounds in oilseed rape.
5. To evaluate the efficacy of granular silicate treatment on the palatability of wheat to rabbits, we carried out a two-choice bioassay using captive wild rabbits (given a choice of untreated wheat, and wheat grown in soil with added PFS at 1 t Si/ha). Following treatment with PFS there was a 29 % reduction in the proportion of plants that received severe and potentially lethal damage (P<0.05). Furthermore, a higher proportion of the treated plants were undamaged (33 % increase over controls (untreated)). The overall consumption of silicate-treated wheat was reduced by 22 % (dry wt.) in comparison with controls. Following the encouraging results of the bioassay, we tested the effects of PFS in the field in a trial carried out on two consecutive years. PFS was applied at three application rates, 0, 1 and 5 t PFS/ha to replicate plots of three wheat varieties. Rabbits were introduced to the plots when the wheat plants had grown sufficiently large to sustain the population. Samples of wheat and soil were taken at regular intervals throughout the trial and the concentration of silica and the rabbit damage sustained by the plants assessed. PFS treated plants (5-t/ha) contained up to 70% higher levels of silica in their tissues than control (untreated) plants; immediately following the first application of PFS, bio-available silica in the soil was also significantly higher in treated plots (32.9, 56.2 and 80 µg Si / g soil for 0 (control), 1 and 5 t/ha plots respectively). Assessment of damage taken soon after the rabbits were first introduced in the first trial, showed that the total number and severity of plants damaged in the 5 t/ha plots were less than in control plots (there was a 48% reduction in the proportion of plants damaged by rabbits in the 5-t/ha plots compared 0-t/ha plots in the first two assessments). A second trial is still underway, however, the preliminary results look promising (dry plant weights in the 5 t/ha plots up to 29% higher than controls have been recorded). The plots are due to be harvested in August, and once completed the results will be presented under the follow-on project (WM0401).
6. Moore et al. (1999) estimated the national cost of badger damage to crops to be between £6.5 and 12.5 million per annum. They suggested that future research into badger management options should target direct crop damage to wheat, maize etc., and burrowing damage. Project VC0404 concluded that badgers may be able to make ‘taste-odour associations’ between an odour and the unpleasant ingestional effects of a Ziram-based repellent. Badgers might have used the odour as a cue to which baits were unpalatable (Baker et al. in prep). As visual cues can enhance the effect of avian repellents, we proposed that an odour cue might help protect crops from badger damage, following creation of a ‘taste-odour association’ using a bi-sensory formulation of Ziram and a pleasant odour.
7. A series of trials were designed and undertaken to test the efficacy of the bi-sensory approach. The trials were conducted in three phases: baseline phase - presentation of untreated food at untreated feeding sites; conditioning phase – presentation of ziram-treated food in a feeding site treated with clove oil; and a post-conditioning phase – presentation of untreated food at a feeding site treated with clove oil. Once conditioned to associate the presence of clove oil with ziram-treated food, the presence of clove oil alone was sufficient to reduce badger feeding and activity. When used in isolation (without ziram) clove oil was shown to have little or no repellent activity against badgers. Under this test paradigm the bi-sensory formulation was shown to be more effective in reducing badger activity during the post-conditioning phase, than the commercially available form of Ziram (AaprotectTM). The potential of the bi-sensory approach in crop protection was also tested. In this paradigm, a bi-sensory formulation was used to protect maize cobs from badger feeding damage. Again, following a conditioning period in which the badgers were trained to associate ziram-treated maize cobs with a feeding site treated with clove oil, the presence of clove oil alone in the post-conditioning phase was sufficient to reduce feeding damage.
8. It is recommended that future research be undertaken to test the efficacy of this approach in protecting crops in field-scale trials. As badger damage to crops is seasonal, the trials should determine the optimum timing and duration of conditioning and post-conditioning phases required for the protection of the particular crop. The bi-sensory formulations should also be optimised for suitable application and persistence for the particular crop requiring protection.
9. We have previously shown (VC0404) that capsaicin is a very effective repellent against grey squirrels. The key characteristic of this molecule is its potency (0.05% w/w a.i. sufficient to abolish feeding of treated diet by squirrels). The aim of this study was to develop a cost-effective formulation of capsaicin that could be used to provide local protection against grey squirrels in domestic and amenity settings.
10. A cost-effective formulation of the repellent capsaicin was developed which was suitable for spraying using conventional equipment. The formulation was evaluated in a two-choice feeding test (capsaicin was applied to peanuts at 0.05 % w/w) using both captive and free-ranging grey squirrels. The capsaicin spray application was extremely effective (over five different sites the treated peanut consumption was less than 5 % of the total peanut consumption). It is recommended that the capsaicin formulation is further evaluated in trials targeted at solving other localised grey squirrel problems in domestic or amenity settings. The formulation should be adapted to optimise the targeting and persistence of capsaicin for the particular situation, whilst maintaining its cost-effectiveness and ease of application.
CSG 15 (9/01) 3
Projecttitle / Development of repellents against vertebrate pests with special
reference to rabbits, badgers and grey squirrels / DEFRA
project code / VC0414
Scientific report (maximum 20 sides A4)
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CSG 15 (9/01) 3
Projecttitle / Development of repellents against vertebrate pests with special
reference to rabbits, badgers and grey squirrels / MAFF
project code / VC0414
General Background
Traditional methods of controlling problem wildlife, such as poisoning and trapping, are often ineffective, environmentally hazardous, socially unacceptable or uneconomic while advice on effective, non-lethal approaches is increasingly in demand. Hitherto the research for humane alternatives has been surprisingly unimaginative, yet for economic and sociological reasons, finding such alternatives is important to the future of effective but acceptable wildlife management. Repellents offer a benign alternative to lethal methods for reducing the problems posed by problem species. A three-year research project (VC0404) made considerable progress towards the development of humane and cost-effective repellents for use with rabbits, badgers, foxes and grey squirrels. The aim of this project was to build on this work in relation to (1) systemic applications to enhance crop resistance to rabbit damage, (2) the use of multi-sensory formulations as badger repellents and (3) capsaicin as a grey squirrel repellent, and thereby assist DEFRA in meeting its policy objectives to ensure safe, effective and humane methods of controlling UK vertebrate pests.
Scientific Objectives 1 & 2: Develop a method of spray and/or fertiliser application of silica as a technique for protecting crops against rabbit damage & evaluate the effectiveness of reducing the palatability of crop plants for rabbits as a means of reducing damage, including assessment of effects on rabbit ranging behaviour.
Systemic silicate application to reduce rabbit grazing
Background
In project VC0404 the elevation of natural plant defence strategies was identified as an exciting new approach to the management of vertebrate pests. Previous studies, in which the systemic application of plant defence precursors reduced the palatability of oilseed rape to pigeons and hence the damage they sustained, have provided proof of concept (Grey et al. 1997). Wheat plants lack the diverse secondary defence chemistry of oilseed rape. However, like many grasses, they do have a number of physical defences to deter herbivores including dense rosettes of leaves and leaf trichomes made of silica. Leaf silicification, in the form of hair-like trichomes and a silicated epidermal layer, is important in the defence of monocotyledonous plants such as wheat against herbivory. Vertebrate herbivores actively discriminate between high and low silica grasses and preferentially feed on the latter (McNaughton & Tarrants 1983). This avoidance of high silica plants is attributed to the increased mechanical abrasion of enamel surfaces Baker et al. (1959), and the ability of ingested silica to cause internal malaise (Harbourne 1991).
Systemic application of soluble silica (sodium silicate) significantly raises the levels of leaf silicates in wheat plants (Grey et al. 1996). This in turn has been shown to enhance the wheat plants’ resistance to rabbit damage in laboratory scale trials (VC0404). Preliminary studies have shown that a spray application of sodium silicate significantly elevates levels of wheat leaf silicates; however, field application of this method may be costly. A more cost-effective option may be slag (calcium silicate) fertilization. Silicate fertilisation has long been an established method for increasing plant development, growth and yield in many graminaceous and some non-graminaceous crop species. It has also been known to increase disease-resistance of plants, especially in rice (Datnoff et al. 1997), where the mechanism of induced resistance is attributed to the formation of a silicated epidermal cell layer (Takahashi 1995).