Potential of Repellents for Control of Predation by Mustelids, Rats and Possums in New Zealand

Potential of repellents for control of predation by mustelids, rats and possums in New Zealand

B. Kay Clapperton

56 Margaret Avenue, Havelock North 4130, New Zealand Email: [email protected]

~~~~~~~~~~~~~~~~~~~~ Dr B K Clapperton Wildlife Scientist & Editor

Abstract To achieve widespread control of rats (Rattus rattus, R. norvegicus), stoats (Mustela erminea) and other mustelids, and brushtail possums (Trichosurus vulpecula) in New Zealand, we need to utilise as many combinations of control strategies as possible. Repellents could be used in island/border protection, push-pull strategies for protection of specific sites, to re-direct foraging behaviour or even in mating disruption. I review the recent literature to identify potential primary and secondary chemical repellents and briefly assess the options for auditory, visual and mechanical repellent devices. Chemical repellents include predator odours from urine, body and fur, as well as alarm pheromones and specific glandular secretions. While these odours can induce defensive behaviours, odours from familiar predators have not been shown to be effective repellents in field applications. It is not clear whether this lack of response is concentration- dependent. Odours from non-familiar as well as familiar predator sources may be worth investigating, including fear-inducing urinary compounds from large felines and mustelids. Identified active components of predator odours, including 2,5-dihydro-2,4,5-trimethylthiazoline, pyrazines, pyridines, 2-phenylethylamine, butanoic and butyric acids should be assessed as repellents for pest species in New Zealand, as should 4-methylpentanal and hexanal from rat alarm pheromones. Repellents can also be sourced from plant secondary metabolites and innately irritant or obnoxious odours. Potential plant-derived repellents include a range of essential oils and terpenes (e.g.; capsaicin, piperine, pulegone), methyl nonyl ketone and acetophenones. Compound that induce conditioned food aversion or place avoidance that are worth considering for use especially against egg predation include carbachol, fluoxetine hydrochloride, clotrimazole, anthraquinone and methyl anthranilate. I assess the limitations of the use of repellents and both the behavioural and ecological complications in converting effective laboratory-tested compounds into repellents that will be effective in the field. The roles of odour concentration and habituation issues need to be considered. I emphasise the need for combining chemical repellents into realistic odour mixes and using multi-sensory repellent systems to maximise efficacy, and the use of repellents in conjunction with other control strategies.

Keywords: repellent, deterrent, semiochemical, plant secondary metabolite, pest control, rat

Rattus spp., brushtail possum Trichosurus vulpecula, mustelid Mustela spp., cat Felis catus

Contents 1. Introduction ...... 5

1.1 The need for repellents in New Zealand predator control ...... 5

1.2 Potential repellent strategies ...... 5

1.3 Repellent characteristics and mechanisms ...... 6

1.4 Sources of repellents ...... 9

1.5 Aim of this review ...... 10

2. Predator odours as kairomones ...... 11

2.1 Predator odours from different body parts are not equivalent ...... 11

2.2 Predator odours as feeding suppressants for herbivores ...... 15

2.3 Active components of predator odour repellents ...... 15

2.4 Effect of diet of predators on repellency of odours ...... 20

2.5 Effects of concentration and age ...... 20

2.6 Effect of evolutionary, ecological and individuality pressures ...... 21

3. Allomones and other animal products ...... 22

3.1 Allomones ...... 22

3.2 Conspecific odours—alarm pheromones, stress odours and scent marks ...... 24

4. Plant-derived repellents ...... 25

4.1 PSMs as rodent repellents ...... 27

4.2 PSMs as possum repellents ...... 32

4.3 PSMs as carnivore repellents ...... 33

5. Conditioning stimuli for aversion learning ...... 34

6. Other chemical repellents ...... 36

7. Visual, auditory and mechanical repellents ...... 38

7.1 Visual repellents...... 38

7.2 Acoustic repellents ...... 39

7.3 Mechanical repellents ...... 41

8. Combination repellents ...... 42

9. Conclusions ...... 43

9.1 Predator odours ...... 43

9.2 Plant-based repellents ...... 46

9.3 Repellent identity and test procedures ...... 47

9.4 Repellent commercialisation and application ...... 48

10. Acknowledgements ...... 49

11. References ...... 49

1. Introduction

1.1 The need for repellents in New Zealand predator control

Invasive mammals, including three mustelid species—stoat (Mustela erminea), ferret (M.. furo) and weasel (M. nivalis); rats—ship or black rat (Rattus rattus) and Norway or brown rat (R. norvegicus); the feral cat (Felis catus) and brushtail possum (Trichosuru vulpecula) are significant predators of the native fauna of New Zealand (Towns et al., 2001, Innes et al., 2010, Ruscoe et al., 2013). Pest control for conservation gains in New Zealand has moved from targeting predators in discrete areas to protect specific vulnerable native species to a bolder vision of a mammalian-predator-free mainland over a 50-year time frame (Russell et al., 2015). Achieving this goal will require a multi-faceted approach, with not only new technologies but better deployment of standard techniques and their integration into a system that is based on sound knowledge of the behaviour and ecology of these pest species. Repellents could be a component of such a system. A repellent has been defined as a stimulus that causes an organism to make orientations away from the source (Nordlund et al., 1981) but also any stimulus that prevents a pest from locating or recognising the target host or prey organism (Deletre et al., 2016b). These stimuli can work via a range of sensory processes. They include deterrents that disrupt feeding behaviour.

1.2 Potential repellent strategies

Repellents could be used to prevent predators from approaching an area or object, for example bird nests. They could be particularly useful in preventing re-invasion of islands (Oppel et al., 2011) and other areas where pests have been removed — if deployed at ports and wharves, even on mooring ropes, to stop stowaways on boats, gaps in predator fences, key access points to valleys, etc. Repellent strategies can also be used to minimise bait station monopolisation by individual pest animals (Cagnacci et al., 2005).

Repellents could become part of mammalian ‘push-pull’ or ‘stimulo-deterrent’ diversionary strategies (Deletre et al., 2016b, Wyatt, 2003), as are used in insect pest management. They are defined as ‘the behavioral manipulation of [insect] pests and their natural enemies via the integration of stimuli that act to make the protected resource unattractive or unsuitable to the 5 pests (push) while luring them toward an attractive source (pull) from where the pests are subsequently removed.’ (Cook et al., 2007, p. 375). This could take the form of trying to redirect the movement patterns of a predator away from a prey towards a control device, a form of behavioural interference. Or it could be used to make prey food less attractive thus increasing the relative attractiveness of nearby toxin baits or trap lures. For herbivores, deterrents applied to a target crop can be combined with planting of a ‘lure crops’ nearby (Kimball and Taylor, 2010). Repellents also have some potential to influence where pest species will settle following disturbance (Jones et al., 2016).

Another potential role of repellents is in mating disruption. They could be used to affect interactions between conspecifics e.g., to reduce breeding success or induce weight loss. There is a substantial literature on the impact of predation risk on the reproductive success of small mammals and other species (Carlsen et al., 1999, Apfelbach et al., 2001, Wang and Liu, 2001, DeGabriel et al., 2009, DeGabriel et al., 2014, Jochym and Halle, 2012, Clinchy et al., 2013) but this is beyond the behavioural base of this review.

Repellents can also be used to deter non-target species rather than the pest, either to protect species at risk of becoming by-kill or by-catch (Day et al., 2003, Speedy, 2005, Morriss, 2007, Phillips and Winchell, 2011, Clapperton et al., 2014, Cowan et al., 2016, Cowan and Crowell, 2017).

1.3 Repellent characteristics and mechanisms

Repellents can induce the behavioural responses of anxiety or fear. Anxiety is a state of chronic apprehension about future threats, more likely to be induced by indirect cues (Grillon, 2008). Fear is induced by the presence or suspected presence of a real threat e.g., the presence of a predator (Dielenberg et al., 2001a, Clark and Avery, 2013, Dielenberg and McGregor, 2001). Anxiety and fear are mediated via separate neurochemical pathways (Tovote et al., 2015). Vomeronasal receptors (both V1R and V2R) detect chemical signals from putative predators that can induce fear, while ORs are more generalised odour receptors (Fortes‐Marco et al., 2013). Specialised Grueneberg ganglion neurons in the nasal cavity detect and respond to sulphur- or nitrogen-containing compounds that are typically found in predator odours. Schakner and 6

Blumstein (2013) viewed the responsiveness to repellents as a continuum, with low intensity stimuli inducing anxiety that leads to avoidance behaviour, while fearful higher level threat stimuli lead to flight, as do painful stimuli.

Anxiety manifests in defensive behaviour — avoidance, reduced food consumption, freezing or motion reduction (Blanchard et al., 2003), but it may also induce risk assessment behaviours i.e., cautious attention is paid to the predator odour source, rather than retreat (Dielenberg et al., 2001a, Dielenberg et al., 2001b). It is a form of interspecific eavesdropping in which the prey intercepts a signal from the predator (Peake, 2005, Goodale et al., 2010, Hughes et al., 2010b, Hughes et al., 2012, May et al., 2012, Banks et al., 2014).

Fear leads to flight, escape or rigorous retreat behaviour, or freezing. It can also induce less grooming and more defaecation and urination, jumping, rearing, orientation and scent marking (Burwash et al., 1998b, Roberts et al., 2001, Staples et al., 2008, Fendt et al., 2005). It may also lead to prolonged psychological stress and subsequent physiological and demographic changes (Clinchy et al., 2013). While these authors reported some field studies that have provided proof of fear-induced changes in the brains of free-living animals, they noted the lack of studies of the effects of predator-induced stress on the survival, breeding and population densities of mammals, as opposed to studies of other taxa (Preisser et al., 2005). Although there are few studies that demonstrate large-scale changes in spatial behaviour or habitat use in response to repellents, they can affect activity patterns (Hegab et al., 2015). While for some species, predator avoidance is more about hiding rather than running away (Hegab et al., 2015), for some species the reverse is true (Spencer et al., 2014). Indeed the movement responses of prey to predator odours will vary among prey species and habitats (Wirsing et al., 2010).

The degree of learning involved in the response will affect to what extent animals will sensitise or habituate to a stimulus and move up or down on the anxiety (avoidance) to fear (flight) continuum (Schakner and Blumstein, 2013). When novel stimuli are not reinforced with consequences then they do not produce long-lasting repellency (Clark and Avery, 2013).

Aversive stimuli can function as either primary repellents that induce an innate response or as secondary repellents that induce a learned response (Clark, 1997, Shivik et al., 2003). They include chemicals that affect olfaction and taste, as well as visual and auditory systems and electronic and mechanical devices (Mason, 1998, Bishop et al., 2003, Fagerstone et al., 2012). Aversive tastes are likely to be more repellent than aversive odours (Beauchamp, 1995).

Primary repellents have the advantages of employing simple stimulus–response processes and ease of application, and are environment friendly (Sayre and Clark, 2001, Shivik et al., 2003). While most are prone to reduction in efficacy over time as the animal learns that there are no worse consequences (Sayre and Clark, 2001), irritants induce reflexive withdrawal that is not prone to habituation (Clark and Avery, 2013). Some repellents can become more effective over time, if they trigger a response by the trigeminal nerve (Bryant, 1995). This may be because of the intensity of the stimulus (Hegab et al., 2015).

Secondary repellents that rely upon conditioned food aversion (CFA) have been considered as a potential mechanism to repel predators from food sources for decades (Gustavson et al., 1974, Ellins and Catalano, 1980, Macdonald and Baker, 2004). There are commercially available repellents for birds but fewer successful applications with mammals—Clark and Avery (2013) list repellents registered in the US. While there have been a range of deterrent formulations patented over the years for various mammals, especially cats, dogs, rats and mice, none has been proven to be the super-repellent needed to solve our pest problems. As Fall and Fiedler (2015) pointed out, even after decades of investigation, repellents have seldom been put to successful practical use in the control of damage by rodents in agriculture. There have been promising studies in the laboratory but behavioural and ecological complexities make it hard to target wild rodents and carnivores (Smith et al., 2000). Not only is it more difficult to administer and control consumption of conditioning agents in the field but also the exposure to a diverse diet by free- living predators may make it more difficult to establish a persistent CFA (Gentle et al., 2006). The treated baits need to closely resemble the prey item (Dorrance and Gilbert, 1977). One of the reasons protection of sheep from coyote (Canis latrans) predation failed was because the conditioned mutton baits did not closely resemble the live lambs (Conover and Kessler, 1994). Moreover, CFA is designed to prevent consumption but does not necessarily eliminate the

8 behaviours involved in prey killing (Rusiniak et al., 1976, Etscorn, 1978). CFA has shown more promise against egg predators (Nicolaus et al., 1983, Conover, 1990, Dimmick and Nicolaus, 1990, Avery et al., 1995, Maguire et al., 2009, Ferguson, 2016).

The challenges involved in developing an effective CFA-based repellent include the selection of conditioned stimuli that are innately associated with the unconditioned response, and suitable for the pest species (Rabin and Hunt, 1992). The bait formulation must ensure that the conditioning agent is not detectable (Cotterill et al., 2006, Nielsen et al., 2015b), and that the reinforcement is appropriate to the situation—numerous individual predators or a rapid turn-over in the population will require multiple presentation of the repellent (Schakner and Blumstein, 2013). This makes CFA to be of limited application where pest eradication is the aim. It has better application in systems where the aim is just to minimise damage caused by pests, for example where some wiley individual predators have resisted all attempts to remove them using trapping, poisoning or shooting, or where the predators themselves are a valued species.

1.4 Sources of repellents

Chemical signals that emanate from animals of the same or different species can cause attraction or repellency and can act via an innate or learned association with a threat. While Nielsen et al. (2015a) suggested that categorising of animal odours should be based on the odour valence (level of attraction/repellency) and degree of learning involved in the responses, the categories kairomone and allomone are used here to provide clear sub-sectioning of the sources of potential repellent chemicals. Kairomones are ‘interspecific chemical communication substances of animals, bringing benefit to the recipients of the chemical signal’ (Rajchard, 2013, p.561). Allomones ‘evoke, in organisms receiving them, responses that favour the source species’ (Brown et al., 1970, p. 21). Interspecific signals include alarm pheromones that are released in the face of a threat and responded to by nearby conspecifics with a ‘flight or fight’ reaction (Wyatt, 2003) and scent marks that are laid down as territorial defence and assessment of dominance and can evoke a variety of responses (Gosling and Roberts, 2001).

Repellent chemical signals are also released by plants. A wide range of plant secondary metabolites (PSMs) have evolved to reduce consumption by herbivores or to reduce attack by 9 pathogens. These repel mammals via irritation, neophobia and sickness (Mason et al., 2001, Shivik et al., 2003). Or they can act as flavour modifiers, making the plant less palatable to herbivores (Kimball and Taylor, 2010).

There are numerous other illness-inducing compounds that can be associated with odour or taste stimuli to induce CFA, and other chemicals that, while toxic at high concentrations, could be aversive at lower concentration.

As well as chemical repellents, visual, auditory, electromagnetic and mechanical stimuli can also be employed to modify the behaviour of pest species. While many electronic devices have been patented, there is scarce scientific literature available in support of their efficacy (Zhelev et al., 2018).

1.5 Aim of this review

The aim of this review is to summarise the recent literature on the responses of rodents, carnivores and possums to chemical repellents, with a brief overview of sound, visual and mechanical repellents and how they can be combined in multi-sensory devices. Where possible I focus on research that demonstrates effectiveness of repellents under field conditions and behavioural responses to repellents that could have direct pest control implications.

I identify the most promising repellents for the target predators in New Zealand and outline the potential for repellents based on other sensory modalities, with the thought in mind that multisensory repellents might have more potential than single-source systems.

I do not include a comprehensive review of all the literature as there have been major reviews published elsewhere (as listed under the relevant sections below). I only touch on the neurosensory mechanisms involved in repellency, that have been well reported (e.g. Li and Liberles, 2015, Liberles, 2015), nor do I summarise all the studies that use physiological changes and assessment of neural processing to measure fear and avoidance responses. Clinchy et al. (2013) reviewed the knowledge of how predation risk can affect psychological stress and its physiological consequences. 10

Greggor et al. (2014) argued that while much is known about behavioural and cognitive processors of animals, this knowledge has been poorly used for achieving conservation outcomes. The challenges faced in applying this knowledge was emphasised by Schakner et al. (2014), who noted that simplified laboratory experiments often fail to account for the wide array of competing stimuli and individual variability in response found in the natural world.

2. Predator odours as kairomones The scents released by predators can act as kairomones when prey species respond to them. The potential of predator odours as repellents can be informed from both the animal behaviour literature and the medical research aimed at understanding responses to stress, as well as studies on pest control. Much of this work has been summarised in the last 20 years. Kats and Dill (1998) described the range of responses to predator odours of animals from a variety of phyla and Hegab et al. (2015) provided a broad overview of the responses of mammals to predator odours. Jones et al. (2016) developed a model that incorporates the various ecological factors that can affect how one species will respond to the scent of another species. Fagerstone et al. (2012) outlined the history of mammalian repellent research at the US National Wildlife Research Center, where the emphasis was on research on rodents. Apfelbach et al. (2005) gave a comprehensive review of the effects of predator odours on their prey, and Banks et al. (2014) related this knowledge to the interrelationships between mammalian species in Australia. Only the more recent literature and the most relevant studies to New Zealand pest control are covered in this review.

2.1 Predator odours from different body parts are not equivalent

Prey species will respond to predator odours but not all odours are equivalent. Ferret odours from fur and skin induced stress responses in rats but those from ferret faeces, urine or anal gland secretions did not (Masini et al., 2005). Body odours are more likely to be repellent as they indicate the close presence of a predator (Blanchard et al., 2003, Hegab et al., 2015, Jones et al., 2016). Scent from skin glands is likely to be more volatile and less persistent than the scent from faeces and urine (Jones et al., 2016). But Apps et al. (2015) considered that it was the high 11 molecular weight/low vapour pressure compounds that do not disperse far from the predator’s body that may be the indicators of high predator risk. Thus aldehydes that tend to be released directly from terrestrial vertebrate bodies rather than being placed in the environment as scent marks may serve as repellents for prey species.

While many studies have been conducted on the responses of captive-bred Norway rats—the ‘Lab’ rat— to both urine, faeces and body odours of predators and a few on brushtail possums, there have been fewer studies on the responses of ship rats and stoats. There have been a few studies on the responses of prey species on the repellent effects of mustelid anal gland odours and their use as herbivore feeding suppressants, summarised by Lindgren et al. (1995). There has been some progress made on identifying the individual chemicals involved in defensive response. Factors that can affect the responsiveness of animas to predator odours include the effects of diet of the predator, the concentration and age of the scent, seasonal effects and evolutionary pressures, as discussed below.

Responses of rodents to urinary and faecal odours Some but not all early studies on the responses of rodents to odour stations or scented traps indicated that the odour of predator urine or faeces was repellent (reviewed by Apfelbach et al., 2005). Notably, ship rats and Pacific rats (kiore, Rattus exulans) were more often caught in live traps in Hawaii scented with mongoose (Herpestes auropunctatus) faeces than mongoose urine (Tobin et al., 1995). Odours from cat urine and faeces were shown to have no effect on ship rats or kiore in a New Zealand study (Bramley and Waas, 2001); while some adult Norway rats showed aversion to cat urine, the results varied between the two populations and amongst individuals tested (Bramley et al., 2000). Cat urine did not induce defensive behaviour in naïve ‘Lab’ rats, unlike the urine of larger felids and canids (Fendt, 2006). The author suggested that the bladder source of the urine, domestication or diet of the cats were the likely reasons for this lack of repellency. Recent studies have shown that bladder urine of feral cats incorporated into maize feed was avoided by captive multimmate rats (Mastomys natalensis), with a stronger effect being produced by female urine than male urine (Mulungu et al., 2016, Mulungu et al., 2017). The rats demonstrated freezing and risk assessment behaviour. Cat faeces did not reduce foraging of mice (Mus musculus) (Shapira et al., 2013). Urine samples from a range of felid and

12 canine predators did not repel wild Norway rats from foraging in their familiar territories (Stryjek et al., 2018).

Fox (Vulpes vulpes) urine induced avoidance behaviour in ‘Lab’ rats (Wernecke et al., 2015). The rats also moved food away from an area perceived as a high predator risk site because of the presence of fox urine (Wernecke et al., 2016). Russell and Banks (2007) also showed that bush rats and swamp rats (Rattus lutreolus) showed avoidance of fox faeces. Kovacs et al. (2012) found that only juvenile but not adult bush rats reduced foraging activity in the presence of fox odour, and this effect was stronger in areas of high fox density. Moreover, Carthey and Banks (2018) found that, while ship rats in Australia recognised dog and fox odours, they did not show antipredator behaviours towards them.

While field voles (Microtus agrestis) have been shown to reduce daily range sizes in the presence of stoat urine and faecal odour during the breeding season (Borowski and Owadowska, 2001), wild-caught Norway rats were not repelled by the urine and scats from stoats (Murphy et al., 2014). A recent study has found that bank voles (Myodes glareolus) consumed fewer beech nuts when they were treated with mink (Mustela vison) excrement (Villalobos et al., 2018).

Responses to anal gland odours Anal gland odours that are used in small quantities as territorial markers may be perceived by the prey species as an indicator of a low predator risk — these scents are left behind in the environment and may be valuable for intra-specific communication but do not necessarily indicate the presence of the predator itself. Apfelbach et al. (2005, p. 1140) concluded that anal gland odours do not appear to induce ‘rapid aversive cue and context conditioning when used as unconditioned stimuli’. The release of anal gland odours in large quantities as defence allomones is discussed below. While there have been few recent studies on the responses of rodents to mustelid or cat anal gland odours, synthetic analogues of some of their active ingredients have been assessed (see below).

Responses to fur and body odour The responses of ‘Lab’ rats to the odour of domestic cat fur have been used in the study of fear and stress. The relevant early literature is well covered by Dielenberg and McGregor (2001).

Depending upon the experimental apparatus, responses include avoidance of the odour source and increased time sheltering and/or risk assessment behaviours. In rats these include ‘stretch- attend’, ‘head-out’, ‘flat back approach’ and ‘vigilant rearing’ (Blanchard et al., 1991b, Blanchard and Blanchard, 1989, Dielenberg and McGregor, 2001). Responses were observed to be long lasting and did not require previous experience with a real cat but habituated over time and needed very close contact (<= 5 cm) with the odour source, possibly because the odours were not highly volatile. Rat pups, possibly as young as 18 days old, showed defensive responses to cat fur odour (Hubbard et al., 2004). Muñoz-Abellán et al. (2008) and Muñoz-Abellán et al. (2009) showed that cat fur odour induced avoidance behaviour and a conditioned fear response in ‘Lab’ rats and related these findings to neurophysiological responses. May et al. (2012) showed that ‘Lab’ rats reduced food consumption in the presence of cat body odour.

Little is known about the response of rats to the odour of different individual cats — especially male v. female odours. Muñoz-Abellán et al. (2010) reported that long-term conditioned aversion of ‘Lab’ rats to cat odour did not differ when the odours came from the fur of either an ovariectomised female or intact males. But the ability to discriminate the odour of different individual predators may be an important determinant of response; if the prey species that can determine that there are numerous individual predators nearby they will perceive a higher predation threat than if the scent is clearly coming from one individual (Jones et al., 2016).

There have been no published studies on the responses of either wild Norway rats or ship rats to cat fur odour. In a captive trial on wild-caught ship rats reported by Carter (2012), exposure to cat bedding odour induced approach and mouthing, i.e. investigatory rather than avoidance behaviours. Themb’alilahlwa et al. (2017) found that it required the presence of both cats and dogs, not just cats, to reduce activity and foraging behaviour of free-living ship rats in rural Swaziland villages and suggested that odour cues were only part of the repellent mechanism. These findings together suggest that cat odour is not a promising stand-alone candidate for a rat repellent.

The responses of rodents to mustelid and other predator odours have also been investigated. Stoat and weasel odours have been linked with changes in reproduction, reduction in feeding and 14 seasonal trapping success in voles (summarised by Apfelbach et al., 2005). Male ‘Lab’ rats’ response to the scent of ferret body odour included avoidance and risk-assessment, but not freezing behaviours, and these responses do not habituate (Masini et al., 2005, Masini et al., 2006). Neither captive nor free-ranging ship rats studied by Carter (2012) showed avoidance of stoat body odour — in fact the rats (especially the males) showed investigatory behaviours. Male stoat odour was investigated more than female stoat odour but this may have been just because it was a stronger odour source. The odour samples may have included faecal and urinary odours that could overpowered the fur odour and are not so repellent as fur odour. Ferret body odour did not decrease the visitations of ship rats to scent stations (Garvey et al., 2017).

2.2 Predator odours as feeding suppressants for herbivores

Some early papers demonstrated the repellent effect of predator odours on herbivores. Apfelbach et al. (2005) summarised the findings for a range of species of voles, woodchucks, wallabies, mice, rabbits and hares, as well as brushtail possums. The study by Woolhouse and Morgan (1995) showed that possum browsing damage was reduced in the presence of mustelid-derived odours or fox urine. Miller et al. (2008) found that PlantPlus, a dog-urine based product deterred wild-caught captive brushtail possums from browsing on eucalyptus seedlings.

It is not always clear whether the ability of predator odours to reduce foraging behaviour was due to a recognition of the scent as a predation threat or just because the scent material smelt or tasted foul (Rosell and Czech, 2000). An additional effect of the predator odours’ attracting additional predators to the area and thus increasing predator pressure was suggested by Sullivan et al. (1988).

2.3 Active components of predator odour repellents

There is some evidence that individual or simple combinations of compounds from predator odours are sufficient to repel prey (Zhang et al., 2007, Apfelbach et al., 2015a, Rosen et al., 2015). Stoddart (1980) suggested that certain components of predator urine might act as a ‘leitmotif’ that defines it as ‘predator’. Bowles et al. (1974) identified nitrogen as a primary component of rodent repellents. In a study on dog faeces, Arnould et al. (1998) found that a combination of fatty acids and neutral components produced the strongest repellent effect on

15 sheep. Sulphurous compounds commonly produced in urine and faeces have been considered to be strong candidates for repellents (Nolte et al., 1994b).

Sulphurous compounds are also the main sources of the malodorous scent from mustelid anal sac secretions, with many compounds common to various species (Schildknecht et al., 1976, Crump, 1980a, Crump, 1980b, Brinck et al., 1983, Wood et al., 1991, Zhang et al., 2002). Of these compounds, n-propylthietane (PTA) has been investigated extensively as a repellent. It was avoided by mice (Sievert and Laska, 2016) and has been shown to suppress feeding behaviour in male ‘Lab’ rats (Heale and Vanderwolf, 1994) and possums (Woolhouse and Morgan, 1995). However, Bramley and Waas (2001) found that neither ship rats nor kiore avoided PTA in a Y- maze or at bait stations in the field. Possums were not deterred from feeding at bait stations by PTA (Bramley and Waas, 2001).

Ship rats reduced food consumption and avoided the side of an arena containing 3,3-dimethyl- 1,2-dithiolane (DMDIT; a mustelid anal gland secretion component) (Burwash et al., 1998b) but showed no consistent aversion to DMDIT in field tests in Hawaii (Burwash et al., 1998a).

Sievert and Laska (2016) showed that 3-methyl-1-butanethiol, a major component of skunk [genus Mephitis] anal gland odour (Andersen and Bernstein, 1975, Wood et al., 2002) was avoided by mice. The major component of striped polecat (Ictonyx striatus) is 2- ethylthiacyclobutane (Apps et al., 1988), but its repellency to prey species has not been reported.

The anal gland odours of the largest member of the mustelid family, the wolverine (Gulo gulo), contain a different array of volatile and non-volatile compounds from those of the genus Mustela (see Table 1) (Wood et al., 2005). This could make them a potential source of compounds that could repel rather than attract stoats, weasels and ferrets.

2,5-Dihydro-2,4,5-trimethylthiazoline (TMT) is a highly potent single-component repellent from the faeces of foxes. ‘Lab’ rats can discriminate the odour down to 1 part in 100 billion (Laska et al., 2005). Fendt et al. (2005) summarised the studies from the 1980s through to 2005 on the autonomic and behavioural responses of rodents to TMT. There have been conflicting results on 16 whether TMT acts as a fear-inducing agent or not. A wide range of experimental protocols and chemical concentrations have been used, with the responses to TMT being context-specific. Fortes‐Marco et al. (2013) contended that TMT is aversive but not fear inducing in mice. McGregor et al. (2002) noted that rats do not show the ‘head out’ risk assessment behaviour to TNT typical when presented with cat body odour. But Endres et al. (2005), Fendt and Endres (2008) and Endres and Fendt (2009) concluded that TMT is truly a fear-inducing compound as it induced freezing behaviour not just avoidance behaviour. Freezing reactions did not habituate (Wallace and Rosen, 2000). However, exposure to TMT induces different biochemical responses in the brain of rodents compared with exposure to cat odour (Morrow et al., 2002, Day et al., 2004, Kobayakawa et al., 2007, Staples et al., 2008). It can elicit fast wave bursts in regions of the rat brain in a similar way to PTA, some phytochemicals and organic solvents (Heale et al., 1994, Zibrowski et al., 1998).

Despite the extensive studies of TMT on ‘Lab’ rats, there have been few tests on other rat species or field verifications of its repellency. Burwash et al. (1998b) found that both TMT and another fox faeces/urine component 4-mercapto-4-methylpentan-2-one were avoided by ship rats and reduced food consumption. However, field testing in Hawaii revealed no significant effect of exposure to TMT encapsulated in slow-release devices on capture rates of free-ranging ship rats in an orchard (Burwash et al., 1998a).

A variety of other possible aversive semiochemicals have been found in carnivore urine, including bioamines, pyrazines, pyridines and proteins. 2-Phenylethylamine (PEA) is a biogenic amine found in the urine of carnivores. It is found in particular high concentrations in the urine of large feline species (Ferrero et al., 2011). These authors showed that PEA induced avoidance behaviour in both rats and mice. Wolverine urine contains 2-heptanone, 4-heptanone and 4- nonanone, all of which are potential rat pheromones (references cited in Clapperton et al., 2017).

Pyrazines are common insect defence compounds (Guilford et al., 1987, Dettner, 2014) but are also found in mammalian urine (Apps, 2013, Osada et al., 2014, Apfelbach et al., 2015a) and are detected by odorant-binding proteins in mammalian nasal mucus (Tegoni et al., 2000). Zhang et al. (2007) found that mice were inhibited by a high-concentration combination of three ferret 17 urinary compounds: 2,5-dimethylpyrazine, 4-heptanone and quinoline. Pyrazine derivatives from wolf (Canis lupus) urine have been identified as aversion- and fear-inducing compounds (Osada et al., 2015, Osada et al., 2014). 2,6-Dimethyl pyrazine, trimethyl pyrazine, and 3-ethyl-2,5- dimethylpyrazine caused mice to freeze (Osada et al., 2013). 2,3-Dimethylpyrazine, 2,3- dimethyl-5-ethylpyrazine, 2,3,5-trimethylpyrazine, as well as 3-ethyl-2,5-dimethylpyrazine induced fear-associated responses in further studies on mice (Osada et al., 2017). Deer responded by tail flagging, flight and jump actions to these pyrazines (Osada et al., 2014). However Wolfin, a commercial deer repellent based on wolf urine did not reduce deer browse or road crossings (Nolte et al., 2001, Trent et al., 2001), suggesting that naturally occurring concentrations of pyrazines are not adequate for conservation application.

Nitrogen-containing pyridines found in the urine of the mountain lion (Puma concolor) initiate fear responses in mice. Brechbühl et al. (2015) identified 2,4-lutidine as the most potent Grueneberg ganglion-stimulating and fear- and stress-evoking pyridine. It caused the mice to decrease exploratory behaviour, and increase defaecation, risk assessment and freezing behaviours.

Another nitrogen-containing compound is the ketone ortho-aminoacetophenone. It is a minor component of the urine of male ferrets, and the anal gland secretions of ferrets, stoats, steppe polecats (Mustela eversmanni admirata) and Siberian weasels (M. sibirica fortanieri) (Crump, 1980a, Zhang et al., 2003, Zhang et al., 2005). It has a strong weasel odour and deters birds, mice and ship rats (Mason et al., 1991b, Nolte et al., 1994a, Nolte et al., 1993). O-aminoacetophenone (along with various other acetophenone compounds) acts as an irritant via taste or oral trigeminal chemoreception (Mason et al., 1996, Wagner-Page, 1995).

Rosen et al. (2015) discussed the role of major urinary proteins (MUPs) in producing defensive behaviours in mice. They refer to the studies of Papes et al. (2010), who showed that both the rat MUP rMUP13 and a similar compound from cat saliva, Feld4, were adequate to induce risk assessment and avoidance behaviours. The responses of mice to rat MUPs is concentration dependent (Vasudevan and Vyas, 2013). However, there have been no studies of the responses of rats to Feld 4. 18

L-felinine (2-amino-7-hydroxy-5,5-dimethyl-4-thiaheptanoic acid) is a sulphur- and nitrogen- containing semiochemical found in cat urine (Hendriks et al., 1995). It production is regulated by the MUP cauxin (Miyazaki et al., 2006a, Miyazaki et al., 2006b). Felinine had the same effect as cat urine on reducing reproductive success of mice (Voznessenskaya, 2014) and induced avoidance behaviour in mice that had been sensitised to the odour soon after birth (Voznessenskaya et al., 2016). However, there is limited knowledge about its role in the behavioural ecology of rodents (Pickett et al., 2014). 3-Mercapto-3-methylbutanol is a degradation product of felinine and is probably the source of the characteristic odour of tom cat and bobcat urine (Mattina et al., 1991, Miyazaki et al., 2006b, Apps et al., 2014). It was not, however, avoided by mice (Sievert and Laska, 2016).

Little is known about the chemical composition of body odours of predators but studies are underway. May (2016) analysed the headspace of odours collected from a cloth kept in a cage with a male ferret. Of the 14 identified compounds, hexanal and 2-methylbutyric acid reduced food consumption and increased time spent away from the stimulus in rats (presumably ‘Lab’ rats), but did not produce the whole aversive response associated with real ferret odour.

There may well be many more potential repellent compounds from predator odours. Liberles and Ferrero (2014) patented a method for repelling mice that releases into the air combinations of the following ligands: 2-phenylethylamine, N,N-dimethylcyclohexylamine, 5-methoxy-N,N- dimethyltryptamine, N,N-dimethylphenylethylamine, isoamylamine, N,N-dimethyloctylamine, N,N-dimethylbutylamine and 1-methylpiperidine.

Indeed, combinations of compounds rather than single ‘magic bullets’ may be a more promising approach to the development of repellents. (Apfelbach et al., 2015a, p. 11) considered that: ‘Most often, single volatile substances convey very limited information about the predator. In contrast, arrays of different volatile compounds may convey more relevant information to the receiver’. Sievert and Laska (2016) also recommended investigation of whether mixtures of sulphur-containing odorants would be more effective repellents that single compounds, and

Osada et al. (2013) found that a ‘pyrazine cocktail’ produced a stronger fear response in mice than any of the single compounds.

2.4 Effect of diet of predators on repellency of odours

The sulphurous and or nitrogenous compounds from a high-protein meat diet produce urine, faeces and anal gland secretion odours that distinguish carnivores from herbivores (Nolte et al., 1994b, Scherer and Smee, 2016). This has been experimentally tested. Berton et al. (1998) found that mice took longer to approach the scent of faeces of cats that had been fed a carnivorous diet compared with those fed a vegetarian diet.

But can a prey detect when a predator has eaten conspecifics? Apfelbach et al. (2015b) showed that dwarf hamsters (Phodopus campbelli) could discriminate between the odour of urine from ferrets fed either mice or hamsters. They spent less time near the hamster-scented urine. This odour contained lower concentrations of nitrogen-containing quinolone and o- aminoacetophenone, and three pyrazine derivatives than the mice-scented urine. Cox et al. (2010) showed that goats (Capra hircus) reduced feeding episodes when exposed to faecal odours from predators that had eaten goat. Wallabies (Macropus rufogriseus) showed a similar response to the faeces of domestic dogs that had fed on wallaby (Sharp et al 2016). Striped mice (Rhabdomys pumilio) were more repelled by faeces of snakes that had fed on conspecific mice than on house mice (Pillay et al., 2003).

Wolverine urine contains α-pinene, β-pinene and limononen, possibly because wolverines consume conifer needles (Wood et al., 2009). These are terpenes that may account for the rodent- repellent effects of pine needle and eucalyptus oils (see below).

2.5 Effects of concentration and age

Prey species should invest more energy into predator-avoidance behaviour when the risks are highest (Lima and Bednekoff, 1999). Thus higher intensity or fresher odours are more likely to induce repellency (Hegab et al., 2015). Low concentrations induce only anxiety-related responses, not fear-related responses (Hacquemand et al., 2013). Experimental evidence for this includes the increased freezing and avoidance duration in ‘Lab’ rats in response to increasing

20 concentrations of cat bedding and body odour or TMT (Wallace and Rosen, 2000, Takahashi et al., 2005, Sievert and Laska, 2016), and stronger response from mice to ≥50% compared with 10% TMT (Buron et al., 2007).

Aging of a chemical message modifies its composition and therefore potentially its meaning (Apfelbach et al., 2015a). Prey species might use this variability in predator scent to determine risk of encounter with a predator. For example, aged cat faeces odours did not induce as strong an aversion as fresh cat faeces odours in Brandt’s voles (Lasiopodomys brandtii) (Hegab et al., 2014a). Bytheway et al. (2013) demonstrated that rats foraged longer for food when in the presence of aged predator odour (dog) than when the scent was fresh.

Therefore for the use of predator odours as repellents, formulations may have to include stabilisers or slow-release mechanisms to ensure a constant supply of fresh scent at a fixed concentration. It also suggests that variable results from different studies could be partly the result of the freshness or formulations of the odours sources. This may thus justify the reassessment of ‘unsuccessful’ predator odour repellents.

2.6 Effect of evolutionary, ecological and individuality pressures

The efficacy of predator odours as repellents may vary depending upon the evolutionary or ecological relationship between predator and prey, and amongst individuals. Some prey species respond more to known predators than to those not previously encountered, as summarised for Australian species by Apfelbach et al. (2015a). Yin et al. (2011) showed that wild Norway rats showed stronger avoidance responses to sympatric predators (cats and Siberian weasel urine) than that of an unfamiliar predator (Eurasian badger Meles meles urine). However, predator- naïve wild-caught Norway rats showed aversion towards PTA while those from an area where they might have experienced mustelid predators were not as averse (Bramley et al., 2000).

Responses of prey species to predator odours will depend on the behavioural ecology of the species — Ramp et al. (2005) showed that the social-foraging parma wallaby (Macropus parma) approached synthetic dog odour while solitary red-necked pademelon (Thylogale thetis) avoided the odour. They also noted considerable individual variability in response. Likewise, learned 21 responses to TMT varied among individual ‘Lab’ rats (Endres and Fendt, 2007) and responses to mustelid odours varied among strains of ‘Lab’ rats (Yin et al., 2011). Individuality in responses has also been demonstrated in wild Norway rats (Bramley et al., 2000), rock rats (Zyzomys maini) (Cremona et al., 2015), and brushtail possums (Mella et al., 2015). There may be male– female differences — male ‘Lab’ rats are less risk-averse than female rats (Jolles et al., 2015) so may show less responsiveness to repellents.

The responses of prey species to the scent of predators may also be context-specific. Kavaliers et al. (2001) found that male mice pre-exposed to the scent of a novel oestrous female mouse showed attenuated aversion, avoidance and stress responses to cat or weasel odours. The authors suggested that the perceived presence of a female emboldened the male mice into greater risk taking.

The responses of prey to predator odours can vary in time as well as space. Soltz-Herman and Valone (2000) showed how kangaroo rats (Dipodomys merriami) could be deterred from feeding in shrub habitat by the presence of snake odour, but this effect varied with season. Likewise, Hayes et al. (2006) found that bush rats (Rattus fuscipes) avoided fox (and other predator) faeces only in the dry season.

3. Allomones and other animal products

3.1 Allomones

Many organisms produce allomones as defences against predation. Sometimes the defence chemicals also play roles in intraspecific communication. For example, mice use trimethylamine in intra-specific attraction but it also repels rats (Li et al., 2013)

Similarly, mustelids use their anal gland secretions not only for scent marking their territories but also as a defence mechanism (Clapperton, 1985, Apps et al., 1988, Wood, 1999). They therefore could act as noxious odours with innate repellent characteristics. Even some (but not other) song bird species have been shown to avoid mustelid anal sac secretions (Amo et al., 2008, Amo et al., 22

2011, Johnson et al., 2011). The most noxious odours are produced by skunk species, and alkyl mercatan, the major component of skunk scent (Stevens, 1945) is an active ingredient of commercial dog and cat repellents (e.g. “Skunk Shot”, http://www.connovation.co.nz/vdb/document/100, retrieved 2 July 2017). Its efficacy to repel rodents, stoat and ferrets or brushtail possums has not been reported.

Chemical defences of invertebrates were summarised by Spiteller (2008). Some use simple chemicals like formic acid and acetic acid. Various millipedes and insects, like the Bombardier beetle (Brachynus ballistarius), use benzoquinones. Others use toxins like pederin or cantharadin. Cyanogenic glycosides, pyrrolizidine alkaloids, anthraquinones and cardenolides are also listed. Aldehydes including (E)-2-alkenals are common defence chemicals in many arthropod taxa, e.g. millipeds and stink bugs (Blair et al., 2016). They can be repellent to birds (Staples et al., 2002). E-2-hexanal is aversive to rats, via stimulation of the trigeminal nerve (Blair et al., 2016). ‘Lab’ rats presented with volatile chemicals emitted by live cockroaches (Blaberus giganteus) were observed to jump back, head-shake and groom the nose (Gaoh, 1999). The repellent components were thought to include 7H-1-indeno[2,1-a]anthracen-7-one, 1,2:3,4- dibenzoanthracene, indeno[1,2,3-cd]pyrene, dibenz[a,h]anthracene and benzo[ghi]perylene.

Amphibians often use steroids that can paralyse the predator but are also bad tasting, while snakes have complex formulations of toxic proteins and peptides in their venom (Spiteller, 2008).

Other animal-derived odorous materials are commonly used as feeding deterrents. Herbivores may be deterred from feeding on plants treated with blood, egg and hydrolyzed casein (Kimball and Nolte, 2006, Figueroa et al., 2008, Kimball et al., 2008, Kimball et al., 2009). The likely mechanisms for this action include neophobia, flavour modification and possibly fear (Kimball and Taylor, 2010).

Putrescent egg solids act by CFA using an odour cue. (Bean et al., 1995) found that it was effective against woodchucks (Marmotta monax). They are formulated into effective commercial deer repellents, e.g. Deer Away® (Witmer et al., 1995, Trent et al., 2001). Such products have 23 potential as possum repellents. An egg/acrylic mix has been shown to deter brushtail possums from eating food (while bio-dynamic tinctures did not) (Eason and Hickling, 1992). The commercially available egg/grit formulation Sen-TreeTM was an effective feeding deterrent for brushtail possums (Miller et al., 2008). When combined with a low fertiliser regime, Sen-Tree was of similar efficacy as physical stocking tree guards against browsing marsupials (including brushtail possums) on Eucalyptus seedlings (Miller et al., 2009). Treepel is another commercially available ‘rotten egg’ brushtail possum repellent available in New Zealand (http://www.treepel.co.nz/buyinfo.htm accessed 14 July 2017) that has been shown to prevent possum browse on seedling Pinus radiata (Morgan and Woolhouse, 1995).

3.2 Conspecific odours—alarm pheromones, stress odours and scent marks

Pest species could also be repelled by odours from conspecifics. Potential odours include alarm pheromones and other odours released in response to stress, and scent used for marking territories.

Rat produce alarm pheromones that can induce various responses in conspecifics within a close distance (Kiyokawa et al., 2004, Kiyokawa et al., 2006, Inagaki et al., 2009), with pheromones released from different regions of the body inducing different responses. Alarm pheromones tend to be of low molecular weight and do not persist long in the environment (Wyatt, 2003). The pheromone released from the perianal region induced the risk assessment ‘head out’ behaviours as well as increased concealment (Kiyokawa et al., 2013). It decreased exploratory behaviour(Kiyokawa et al., 2006) and increased levels of anxiety (Inagaki et al., 2008). The active component of this odour have been shown to be a mixture of 4-methylpentanal and hexanal (Inagaki et al., 2014).

Mouse alarm chemicals are similar to the sulphur-containing predator odours like TMT, dimethylpyrazines, dithiolanes and thietane. They activate the same Grueneberg ganglion neurons in the brain of male and female mice (Brechbuhl et al., 2013). 2-Sec-butyl-4.5- dihydrothiazole is a component of male mouse urine that, when in combination with other

24 components, can be a sex attractant (Jemiolo et al., 1991), but on its own produces stress and fear reactions in both male and female mice (Brechbuhl et al., 2013).

While rats and mustelids are territorial, artificially applying their scent marks around sites to deter them from approaching areas, birds’ nests, etc, is a very debatable strategy. Scent marks are not used simply as keep-out signals and seldom repel conspecifics. Shivik et al. (2011) showed this experimentally with coyote urine — coyote spent more time at plots artificially urine- marked than control plots, and intruded more into boundary-marked plots than control plots. This is in line with current theories on the roles of scent marks as identifying a territory holder, and carriers of information on sex, age and breeding status of the marker (Hutchings and White, 2000, Ferkin, 2015). However, Ausband et al. (2013) reported success in using a ‘biofence’ of scent marks to prevent wolf packs from entering a park that was traditionally part of their hunting grounds. Apps et al. (2013) bioassayed components of faecal odours of African wild dogs (Lycaon pictus) as potential spatial semiochemicals to use as artificial boundary ranges.

4. Plant-derived repellents Plant secondary metabolites (PSMs) have been the focus of interest as mammalian repellents for decades (Watkins et al., 1996). Iason (2005) and Dearing et al. (2005) summarise the biochemical processes involved in the anti-herbivory action of PSMs and the ecological, behavioural and physiological counter-actions animals have evolved to minimise these negative effects. PSMs include essential oils and terpenes, alkaloids and alkylamids, (di)carboxylic acids, glucosinolates and phenolics (including flavonoids, tannins and phenylpropanoids), courmarins, stilbenes and lignans (Croteau et al., 2000, Wink, 2003, Hansen et al., 2016b). PSMs often act as primary repellents via neophobia, irritation, bitter taste, or bad smell (Wöll et al., 2013). But they can act as unconditioned stimuli for CFA, inducing vomiting, illness or dizziness. They also modify metabolism and can be toxic (Bell, 1981). Other flavour cues can act as the conditioned stimulus, signalling the presence of other deterrent compounds over short distances (Kimball and Taylor, 2010).

While plant essential oils have proven repellency against a range of insect pests (Isman, 2000, Isman, 2006, Debboun et al., 2006, Koul et al., 2008, Nerio et al., 2010, Robu et al., 2015), they appear to have less efficacy against mammals. Copping and Duke (2007) reviewed natural- product crop-protecting agents and provide very little mention of effects on vertebrates. Essential oils are, however, listed as active ingredients in patented rodent and predator repellents (e.g. Katz and Withycombe, 1989, Messina, 2016, Messina, 2017) and Hansen et al. (2016b) noted that there is considerable overlap between repellents recommended for insects and for rodents.

Converting the knowledge of responses of herbivores to plant chemicals into practical population control procedures will require an understanding of the interaction of animal ecology and behaviour with plant nutrition (DeGabriel et al., 2014). There is likely to be considerable variability amongst mammalian species in their responses to plant products, depending upon their feeding habits and physiology. Voles and mice have shown some different and some similar responses to repellents using the same experimental procedures (Hansen et al., 2016a, Hansen et al., 2016c). There can also be different results achieved by testing materials under various laboratory and field conditions. Neem oil was effective in reducing food consumption by voles in the laboratory trial conducted by Hansen et al. (2015), but not in the subsequent cage trial (Hansen et al., 2016c). Even male and female rodents can respond differently to plant-based repellents (Hansen et al., 2016c), but most studies do not report sex differences. Environmental cues can also affect the efficacy of plant-derived repellents. For example, Bean et al. (1995) found that pine-needle oil repelled woodchucks that did not nest near pine trees but was ineffective for those nesting near pine trees.

Repellency will also depend upon concentration of the compounds. Herbivores ‘eavesdrop’ to find food sources, being attracted to low concentrations of potentially repellent PSMs of plants or their total phenolic content but are likely to be repelled by high concentrations (McArthur et al., 2012, Bedoya-Pérez et al., 2014, Dai et al., 2014).

Much of the work to assess the efficacy of PSMs as rodent repellents has been focussed on voles, and this information, along with that about some other rodent species, is summarised by Hansen et al. (2016b), Hansen et al. (2016c). Only some of the most promising candidate repellents are 26 reviewed here, in particular those that have produced positive results on or may have potential for rats or possums (Table 2). No studies were found that assessed the repellency of PSMs to mustelids, but there are numerous feline and canine repellents on the market that indicate potential for PSMs as carnivore repellents.

4.1 PSMs as rodent repellents

Hansen et al. (2016b) highlighted essential oils and their component terpenoids as well as ketones as the most promising candidates for non-toxic rodent repellents, in particular oils from geranium, black pepper, bergamot, fennel, neem and pine needles.

Geranium and bergamot oils have been tested against ‘Lab’ rats and were shown individually and in combination to reduce the number of visits to an area of a test arena (Kalandakanond- Thongsong et al., 2010, Kalandakanond-Thongsong et al., 2011). The addition of peppermint oil and wintergreen oil to bergamot oil also made an effective repellent (Kalandakanond-Thongsong et al., 2011).

Almost all the research on black pepper oil appears to have been done on voles and mice (Fischer et al., 2013a, Hansen et al., 2015, Schlötelburg et al., 2018), although one study found that the addition of black pepper seeds to maize baits reduced consumption by ship rats (Desoky et al., 2014) . Pepper oil contains (Z) (E)-farnesol (Pino et al., 1990) — farnesols are components of both Norway rat and ship rat preputial gland secretions (Ponmanickam et al., 2010, Rajkumar et al., 2010), suggesting an attractant rather than repellent property at least at low concentrations (Archunan, 2013, Clapperton et al., 2017). A major component of black pepper is the pungent and irritant alkaloid piperine. Although it has not been reported as a repellent for rats, it has been shown to activate rat trigeminal ganglion cells (Liu and Simon, 1996). And it is included as a rat repellent ingredient in a patented rodent-resistant polyurethane foam (Yeates et al., 2013).

Pine needle oil contains high concentrations of the terpenes limonene, α-pinene and β-pinene (Macchioni et al., 2003) and has been shown to induce avoidance and/or reduced feeding or gnawing behaviour by pocket gophers, deermice and voles (Epple et al., 1996, Epple et al., 1995, Wager-Pagé et al., 1997). It does not appear to have been tested as a repellent for rats. Some 27 eucalyptus oils also contain α- and β-pinene (Sartorelli et al., 2007, Cheng et al., 2009), and they also contain 1,8-cineole, a well known insect repellent (Isman and Machial, 2006). Eucalyptus oil was repellent to captive Rattus rattus at 3–20% concentrations (Singla et al., 2014, Singla et al., 2013, Sachdeva, 2017). It reduced food consumption but regular exposure was required for a persistent effect, even when the oil was incorporated into long-life wax blocks (Singla and Kaur, 2016).

Methyl nonyl ketone (MNK or undecanone-2) is a major component of the pungent smelling and bitter tasting rue oil (Yaacob et al., 1989). It is a promising repellent against voles (Witmer et al., 2000). Hansen et al. (2016b), summarising the results of two previously published studies (Hansen et al., 2015, Hansen et al., 2016c), reported that a combination of MNK and methyl anthranilate reduced feeding the most by mice. Further trials in an enclosure have confirmed the efficacy of MNK as a vole and mouse repellent, especially when combined with black pepper oil (Hansen et al., 2016a). Similarly Fischer et al. (2013a), Fischer et al. (2013b) showed the repellent effect of MNK on voles, both in T-maze trials and using a foam formulation as an in- soil treatment of burrows. These promising results indicate that trials on rats would be worthwhile.

Another ketone found in plants is acetophenone, which is the basis for synthetic pharmaceuticals. It is also present in some predator odours (see above). Nolte et al. (1995) listed at least 11 acetophenones in their patent for a rodent repellent, following on from research on ortho- aminoacetophenone (Nolte et al., 1994a, Nolte et al., 1993). These commercialisations reinforce the repellent potential of acetophenone derivatives (Fagerstone et al., 2012). Ballinger and Werner (2015) included 2-hydroxyacetophenone along with methyl anthranilate and pepper as trigeminal repellents to be used in a rodent repellent. However, they stated that terpene-based compounds are the preferred trigeminal repellents. Moreover, Spurr et al. (2001) found that ortho-aminoacetophenone at 0.1 g kg-1 did not deter captive Norway rats from consuming toxic baits. Repellent stability would have to be addressed if using ketones as the active ingredients (Thompson, 1990).

The fruit of hot pepper and red chilli plants in the genus Capsicum contain the alkylamide capsaicin and other capsaicinoids, which produce their pungency (Wahyuni et al., 2013). Capsaicin is an irritant that is effective on a range of mammals (Mason, 1998). Small pieces of habanero chilli peppers mixed in coconut fat on beech nuts greatly reduced consumption by bank voles (Villalobos et al., 2018). Synthetic capsaicin reduced food consumption in Norway rats and voles but not birds (Mason et al., 1991a, Witmer et al., 2000). The response to the irritation caused by capsaicin is concentration-dependent (Andelt et al., 1994, Kimball et al., 2009). The degree of food reduction induced by capsaicin can also be affected by availability of alternative foods (Jensen et al., 2003). These authors also suggested that treating nearby preferred food sources with capsaicin has the potential to increase acceptance of toxic rodent baits, thus employing a push-pull strategy. Baylis et al. (2012) found that capsaicin reduced predation by rats (Rattus spp.) on thrush eggs in nests but the predators appeared to habituate to the treatment. Capsaicin can prevent gnawing behaviour as well as feeding (Shumake et al., 1999). This has applications in protection of cables and other manmade structures as well as plants (Shumake et al., 2000, Aley et al., 2015). There are patented devices for rodent control that list capsaicin as an ingredient and outline means of formulation (e.g., (Davidson, 2013, Numata and Willey, 2014). Both volatile oil extracts and non-volatile alkylamides from Szechuan pepper, Zanthoxylum piperitum, have been shown to reduce food intake by Norway rats and voles (Epple et al., 2001, Epple et al., 2004). In the form of capsicum oleoresin, capsaicin has been shown to act as an antifeedant to ship rats (Kaur, 2016)

The phenolic cinnamamide (3-phenylacrylamide) and another cinnamon-derived compound cinnamaldehyde (also known as cinnamic aldehyde; 3-phenylprop-2-enaldehyde) are both effective repellents for birds and mammals, showing primary and/or secondary characteristics (Watkins et al., 1996, Clayton, 1988, Crocker et al., 1993b, Crocker et al., 1993a, Gill et al., 1995, Gurney et al., 1996, Lee et al., 1999, Ngowo et al., 2003). Crocker et al. (1993b) showed that cinnamamide reduced food consumption in wild Norway rats. It reduced pest control bait consumption by captive (wild-caught and ‘Lab’) Norway rats (Spurr and Porter, 1998, Spurr et al., 2001) and induced antignawing activity in mice (Hoiseon et al. 1999 cited in Vijayan and Thampuran, 2004). Kaur (2013) showed that formulations of both cinnamamide and cinnamaldehyde could reduce food consumption and damage to stored foods by male and female 29 ship rats. Babbar et al. (2015) found that a mixture of 5% cinnamaldehyde and sodium bicarbonate reduced consumption by ship rats of wheat stored in bags for at least 15 days. The lack of an initial deterrent effect and feeding behaviour studies confirmed that cinnamaldehyde was acting as a secondary repellent. The rats did not avoid the area around the cinnamaldehyde- treated wheat. Kaur and Babbar (2017) found that 0.4% cinnamamide reduced bait handling in ship rats and the secondary repellent effect increased over time.

Polycyclic quinones can be effective agents of conditioned food aversion but there is limited information about the responses of rats to these chemicals. DeLiberto and Werner (2016) reviewed the literature on the applications of 9,10-anthraquinone (AQ) for pest management and found no other reports on the efficacy of AQ as a rat repellent other than the studies in New Zealand. Clapperton et al. (2015) and Cowan et al. (2015) showed that AQ at rates designed to deter birds reduced palatability and acceptance of pest-control baits to ‘Lab’ rats and captive ship rats, and in field trials in New Zealand there were reductions in kill rates of ship rats (Crowell et al., 2016b). AQ at higher concentrations could be an effective rodent repellent. AQ has varied efficacy on other rodents (Hansen et al., 2015, Werner et al., 2016, Ballinger and Werner, 2018). Ballinger and Werner (2015) showed a reduction in feeding by ‘Lab’ rats when food contained ≥2000 ppm AQ and recommended 0.5–10% AQ when combined with additional PSM repellents.

There is a range of other PSMs that have been suggested as repellents but not so thoroughly studied. Peppermint oil was once considered to be a feeding deterrent for Norway rats (Barnett and Spencer, 1953) and has shown some recent repellent effect (Kalandakanond-Thongsong et al., 2010). Pulegone is one of the major components of peppermint oil. It has shown repellency to woodchucks (Bean et al., 1995) but both Norway and ship rats have been shown to tolerate d- pulegone at concentrations that will deter various bird species (Clapperton et al., 2015, Cowan et al., 2015). This is despite the fact that pulegone is thought to be considerably toxic to rats (Isman and Machial, 2006). Ballinger and Werner (2015) recommended the use of 10–30% pulegone (or limonene or pinene), i.e., higher concentrations than those used as a bird repellent and acceptable to captive possums and ship rats (Clapperton et al., 2015). Issues concerning the stability of d- pulegone would need to be addressed if it was to be used as a key component of a repellent under field conditions (Crowell et al., 2016b). 30

The insect repellent citronella has been shown to reduce feeding in ship rats. Daily application of citronella paint maintained the feeding repellency effect (Singla and Kaur, 2014). It can be effective for 10 days when microencapsulated (Saini, 2018).

Fennel oil needs to be tested against rats, having shown promise as a vole repellent (Hansen et al., 2015). It is listed, among many other essential oils, in a patented vole and mole repellent (Grlica and Wisdom, 2012). Also promising was neem oil. Trials by Singla & Parshad (2007, cited in Singla et al. (2014)), showed that neem oil reduced food consumption in ship rats, supporting the results of trials by Gaoh (1999) on ‘Lab’ rats. Neem seed powder, containing azadirachtin and other bitter compounds, reduced food consumption by ‘Lab’ rats while a commercial neem oil product did not (Gaoh, 1999).

One PSM not researched thoroughly but appearing in some rodent repellent patents (Harding, 1987, Harding, 1989, Harding, 1988) is thujone oil from wormwood, sage and cedar (Gali- Muhtasib et al., 2000, Juteau et al., 2003). The oil is known to have insect antifeeding properties (Alfaro et al., 1981). The peel of citrus plants and dried branches of mugwort are used by farmers in India to repel rats (Sinha, 2014). This may be because mugwort contains camphor, α-thujone and 1,8-cineole and other volatiles (Govindaraj et al. 2008).

Alkaloids are suspected to cause the repellency of Japanese spurge (Pachysandra terminalis) to voles (Curtis et al., 2003). Onion oil was repellent to water voles (Arvicola amphibious) (Fischer et al., 2013a) but garlic oil was not repellent to pocket gophers (Thomomys talpoides) or deer (Odocoileus spp.) (Witmer et al., 1995). Non-volatile astringent tannins are other potential repellents that have not been tested on Rattus species — quebracho has shown to deter feeding of voles (Microtus spp.) (Swihart, 1990, Witmer et al., 2000).

Glucosinolates are found in the pulpy part of fruit of a range of plants. They are not repellent to rodents on their own, but when the seed as well as the pulp is eaten there is a ‘mustard bomb’ hydrolysis effect because the seeds contain myrosinase that acts as an enzyme activating the toxic properties of the glucosinlates (Wittstock and Halkier, 2002, Samuni-Blank et al., 2013). 31

This compartmentalisation concept could potentially be used by pest managers, to target the release of the repellent only when a predator interacts with a device.

4.2 PSMs as possum repellents

Possums have evolved to cope with eucalyptus PSMs (Foley and Moore, 2005). They can metabolise the terpenes α-pinene, β-pinene and 1,8-cineole (Southwell et al., 1980). Wöll et al. (2013, p. 4) reported that: ‘Possums ingest doses of up to 10 g of the essential oil 1,8-cineole per day, doses which would be quite poisonous for human beings.’ Nor did cineole concentration affect foraging behaviour of brushtail possums (Bedoya-Pérez et al., 2014). Lawler et al. (1999) demonstrated that brushtail possums reduced consumption of Euchalyptus leaves with high concentrations of 1,8-cineole but it was the phytochemical jensenone that induced illness. Pass et al. (1998) identified a compound from the polar extract of Eucalyptus ovata that explained the relative deterrent property of some individual trees to common ringtail possums (Pseudocheirus peregrinus). It is named macrocarpal G and is a formylated phloroglucinol compound. However, Marsh et al. (2003) found that brushtail possums had a higher tolerance than ringtail possums for formylated phloroglucinol compounds.

Capsaicin and piperine have been incorporated into a patented rodent-repellent grease that is also supposed to be effective against opossums (Numata and Willey, 2014). However capsaicin, although considered ‘universally repellent to mammals’ (Spurr and McGregor, 2003, p. 13), did not prevent browse of seedlings by brushtail possums when used in the commercial product ‘Hot Shot (Miller et al., 2008).

Extracts from daffodil leaves and bulbs combined with those from catnip leaves and pepper have shown some promise for herbivores including vole, deer, rabbit, raccoon and squirrel feeding reduction (Ries et al., 2001, Curtis et al., 2002), suggesting that these options could be assessed against possums.

Low concentrations of d-pulegone had no effect on bait acceptance or palatability by brushtail possums (Clapperton et al., 2015, Cowan et al., 2015). Low concentrations of AQ did not reduce food consumption or poison baiting efficacy of brushtail possums (Cowan et al., 2015, 32

Clapperton et al., 2015, Clapperton et al., 2014, Crowell et al., 2016b) but 0.25% AQ reduced palatability of baits (Cowan et al., 2015). Cinnamamide surface coated at 0.5% did not reduce bait consumption by brushtail possums (Spurr and Porter, 1998).

Coleman et al. (2006), in a review of the potential alternatives to the use of 1080 poisoning for brushtail possum control summarised the options for chemical repellents. They did not find any post-2000 studies reporting specific trials of plant-derived repellents for brushtail possums. They did provide an assessment of repellent delivery systems, cost effectiveness and technique implementation and integration.

4.3 PSMs as carnivore repellents

There has been little scientific assessment of the potential of plant-based repellent for carnivores and virtually none for mustelids. Nevertheless, there is a range of commercial cat and dog repellents in the marketplace.

Ketones have appeared as ingredients in patented repellents for carnivores (Freeman, 1969, Shotton, 1969, Haase and Tamalenus, 1979, Clayton, 1988, Brown, 2002, Kenney, 2003, Shields, 2015), including repellents to deter cats and dogs from eating slug and snail baits (e.g.Thompson, 1990). MNK is considered to be efficacious, safe and persistent (Freeman, 1969). In combination with cinnamaldehyde, it is considered to reduce damage to rubbish bags by both cats and dogs (Haase and Tamalenus, 1979, Wolski et al., 1984). Katz and Withycombe (1988) found, however, that their formulation of lemon essential oil was more repellent than MNK to dogs.

Cinnamamide has long been known to be repellent to coyote (Lehner et al., 1976) cats and dogs (Copping and Duke, 2007).

Repellents that included essential oils and oleoresins of black pepper and capsicum are promoted as being effective against cats, dogs and skunks as well as herbivores and rodents (Davidson, 2000, Anderson and Davidson, 2015, Anderson and Davidson, 2016).

D-pulegone is found in the eggs of herring gulls, which are not consumed by canids. It has been included in a patented repellent for domestic dogs (Mason et al., 1999).

Tobacco dust has been shown to be repellent to dogs (Huebner 1964 cited in Meuly (1975) but does not appear to be in current use.

5. Conditioning stimuli for aversion learning A range of chemicals have been used as illness-inducing agents for the establishment of place avoidance and/or CFA in mammals, including some of the plant-based products mentioned above. They are listed in Table 3.

LiCl has long been the laboratory standard (Nachman and Ashe, 1973). It is effective on brushtail possums (Clapperton et al., 1996) but has a detectable salty flavour (Burns, 1980). It can reduce food consumption but not prey-killing behaviour in carnivores (Nicolaus et al., 1989c). The potential of AQ and cinnamamide have been noted above. Another bird repellent methiocarb has also been investigated as a repellent for rodents (Reidinger, 1995). Likewise methyl anthranilate and dimethyl anthranilate are bird repellents that have been noted as potential mammalian repellents (Nolte et al., 1994a). Both of these compounds reduced bait consumption in captive Norway rats (5 ’ Lab’ and 1 wild) at 25 g kg-1 but all the rats ate enough to be killed in the no-choice test. Alone or in combination with MNK, methyl anthranilate reduced food consumption by both voles and mice (Hansen et al., 2016c).

Sodium carbonate was not detected by foxes and induced aversion to model eggs (Maguire et al., 2009). The synthetic oestrogenic hormone 17α ethinyl oestradiol has a long-lasting effect on ‘Lab’ rats, as does thiabendazole (Gill et al., 2000). Ethinyl oestradiol was used effectively to deter mammalian predators from consuming hen eggs (Nicolaus et al., 1989a, Nicolaus et al., 1989c). Thiram (tetramethylthiuram disulphide) is a sulphur-containing fungicide that is a secondary repellent to both mammals and birds (Clark, 1998, Kimball and Taylor, 2010). It has shown efficacy against rodents (Johnson et al., 1982, Parshad et al., 1993, Ngowo et al., 2003) and brushtail possums (D. Morgan, Landcare Research, cited in Cowan et al. (2016). A 34 combination of thiram and capsicum was recommended as a repellent to prevent consumption of seeds by mice (Nolte and Barnett, 2000). Ziram (zinc-bis(dimethyldithiocarbamate)) is an agricultural herbicide that has been demonstrated to condition aversions in rodents, herbivores and badgers (Welch, 1967, Baker et al., 2007a). Levamisole produced a stronger CFA in foxes than thiabendazole (Massei et al., 2003a) but oral presentation of this chemical was detectable to both foxes and ferrets (Gentle et al., 2004, Massei et al., 2003b). Massei et al. (2002) showed that ‘Lab’ rats would eat fewer eggs when the taste of egg was associated with thiabendazole. However, the effect was short lived compared with that of thiabendazole-induced CFA to biscuit-based food (Massei and Cowan, 2002). They found that fluoxetine hydrochloride and clotrimazole generated strong, persistent aversions in ‘Lab’ rats.

Antimony potassium tartrate was a more promising CFA-inducing agent than levamisole for ferrets (Massei et al., 2003b). Norbury et al. (2005) trialled ethinyl estradiol, antimony potassium tartrate, lithium chloride, levamisole hydrochloride, paracetamol and sodium monofluoroacetate as illness-inducing agents on ferrets but none of them conditioned a strong enough aversion to consumption of eggs to be considered useful as a conservation technique.

Carbachol (carbamyl choline chloride) has been used to induce CFA in corvids to reduce egg predation (Nicolaus et al., 1989b, Avery and Decker, 1994, Cox et al., 2004, Gabriel and Golightly, 2014, Gabriel et al., 2013, Ferguson, 2016) and also in mongoose (Herpes auropuntatus) (Nicolaus and Nellis, 1987). However, Gill et al. (2000) queried the safety issues surrounding using this chemical at effective doses for rats. Nicolaus et al. (1989b) reported unpublished results showing that ‘Lab’ rats develop food aversion using carbachol as the conditioning stimulus, and recommended it as a potential CFA agent for mammals.

Massei and Cowan (2002) found that aspirin, caffeine, copper sulphate, ipecacuanha, nicotine, nifedipine and xylazine did not reduce food consumption for ‘Lab’ rats adequately to be of use as CFA agents for this species. Cowan et al. (2016) reported unpublished trials by Landcare Research Ltd in which 2% caffeine reduced acceptance and palatability of pelleted baits by both possums and ship rats. ‘Lab’ rats also develop does-dependent aversions to caffeine (White and Mason, 1985). 35

Chemicals used to explore the roles of aryl hydrocarbon receptors (AHRs) in neurophysiological pathways in ‘Lab’ rats have been found to condition food avoidance. Presentation of doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) low enough not to be toxic stopped ‘Lab’ rats from eating chocolate and cheese (Tuomisto et al., 2000, Lensu et al., 2011). Mahiout and Pohjanvirta (2016) found that 6-formylindolo(3,2-b)carbazole, β-napthoflavone and benzo[α]pyrene all induced avoidance of chocolate presented as a novel food. A novel selective AHR modulator C2 also was an effective deterrent. It was not clear to what extent CFA and enhanced neophobia were involved in these results. Two flavonoids, kaempferol-3-O-β-glucoside and quercetin-3-O- β-glucoside, from Euphorbia plants, that in combination were aversive to ‘Lab’ rats (Halaweish et al., 2003), are ligands of the aryl hydrocarbon receptor (Ciolino et al., 1999). It would be interesting to determine the repellent effects of other plant-derived aryl hydrocarbon ligands like curcumin (Mohammadi-Bardbori et al., 2012).

6. Other chemical repellents There is a range of other chemicals that have an innate bitter taste that have potential as flavour modifiers (Kimball and Taylor, 2010). There is debate, however, over whether bitter tastes would deter all mammals. Bitter-flavoured deer and coyote repellents have little efficacy (Wagner and Nolte, 2001, Miller et al., 2014). Nolte et al. (1994a) argued that an aversion to bitterness would be maladaptive for herbivores and Mason et al. (2001) note that bitter-tasting denatonium derivatives appear to have no deterrent effect on most mammals. Pass and Foley (2000), however, conclude that it is the bitter taste of the phenolic glycoside salicin rather than any post-ingestive effects that cause brushtail possums to regulate salicin intake. Beauchamp (1995) considered that carnivores may be more sensitive than herbivores to bitter tastes.

Denatonium benzoate and denatonium saccharide are extremely bitter compounds that have been commonly used as animal repellents, including for rats (Shumake et al., 2000). They are also used at low concentrations to deter humans and pet cats and dogs from eating rodent baits (Kaukeinen and Buckle, 1992). Formulated as a commercial anti-nail-biting product for humans, denatonium benzonate reduced self-mutilation by ‘Lab’ rats (Sporel-Özakat et al., 1991). 36

Picric acid (2,4,6‐trinitrophenol) is a bitter-tasting compound that has shown potential to prevent self-mutilation in peripheral nerve studies on ‘Lab’ rats (Firouzi et al., 2015). It has been considered to have repellent properties (Shearer and Wicker, 1960)). However, picric acid is dangerous to handle (Firouzi et al., 2015) and can be toxic to aquatic wildlife (Goodfellow et al., 1983).

Trinitrobenzene-aniline was recognized in the 1950s as a rodent repellent and herbivore deterrent (Welch, 1954, Welch, 1967, Bowles et al., 1974) and was included in an early patent. However, it does not appear to be in current use.

Butyric acid (butanoic acid) is a carboxylic acid found in butter and other dairy products, and is the noxious smell from human vomit. It induced avoidance behaviour in ‘Lab’ rats (Wallace and Rosen, 2000) and had a deterrent effect on wild Norway rats when mixed into food (Barnett and Spencer, 1953).

β-Chloro-acetyl chloride was an effective repellent for coyotes and dogs but was not considered to be a practicable solution as it is a strong irritant and lachrymator that was likely to affect sheep as well as the predators (Lehner et al., 1976). If it also proved to be repellent to stoats, possums or rats, there may be potential for this compound to be employed in areas away from stock, e.g., arboreally.

The lactones ᵞ-n-alkyl-ᵞ-butyrolactones and ᵟ-n-alkyl-ᵟ-valerolactones have been claimed to have anti-mating effects on dogs (Meuly, 1975) but the mechanisms appears to be simply masking the scent of female dogs.

Carbon dioxide and argon are used to euthanase animals and have thus been assessed for their effect on rat behaviour. ‘Lab’ rats avoid CO2 at concentrations >15% that is not high enough to cause unconsciousness (Leach et al., 2002, Niel and Weary, 2007). While rats will avoid a lethal concentrations of argon (90%), they are less averse to lower concentrations of argon than of CO2

(Leach et al., 2002). The behavioural responses of mink to CO2 have also been examined. 37

Cooper et al. (1998) found that mink would avoid entry into a chamber containing 80% CO2. Mink did not show the same aversive reactions to argon (Raj and Mason, 1999).

Nichols (2016) has suggested that because of sensitivity to ozone, a patented high-voltage spark- producing repellent device works both via a chemical cue as well as light and sound cues to repel unspecified wild and domestic animals.

7. Visual, auditory and mechanical repellents

7.1 Visual repellents

Visual and acoustic repellents usually rely on the ‘startle’ response i.e. neophobia. There may be some avoidance of ‘sign stimuli’ e.g. the response of birds to eye spots (McLennan et al., 1995) but this may be just a response to highly conspicuous novel cues (Stevens et al., 2008, Stevens et al., 2007). Rats are sensitive to light but have poor visual acuity (Burn, 2008).Nor are stoats and possums primarily visual foragers so there is not likely to be the equivalent visual deterrent for these mammals as for birds. Visual cues that rely on neophobia will habituate quickly if not reinforced by negative association.

Fladry, the centuries-old technique that uses coloured flags on ropes to direct the movements of predators away from livestock has received scientific appraisal recently. It has shown some efficacy against wolf but not coyote predation (Musiani et al., 2003, Musiani and Visalberghi, 2001, Shivik et al., 2003, Gehring et al., 2006, Davidson-Nelson and Gehring, 2010, Treves et al., 2016). Modern designs of fladry have been developed using marine vinyl material (Young et al., 2015). Miller et al. (2016) cited a study on wolves that effectively used electrified fladry.

Green light has been touted as a visual repellent for mice because it interferes with nocturnal foraging (Wu, 2015, Wu, 2014). While there appears to have been no scientific verification of this claim, moonlight intensity can affect foraging rates of mice (Shapira et al., 2013). Strobe lights or flashing lights are often used in commercial animal repellent devices (e.g., Pearlman, 2015, Waldman et al., 2017). Trials by the Zero Invasive Predator team confirmed that ‘light on 38 its own seems to be a poor deterrent for rats (ZIP, 2017, p. 14). Light might be of use in a ‘push- pull’ system, enhancing trapping success by helping to direct the movement of some pests, but some preliminary trials reported by Robbins et al. (2007) revealed that neither mirrors nor red LED lights altered the investigatory responses of stoats to baited traps.

7.2 Acoustic repellents

Acoustic repellents may have some potential if they have biological meaning (Baker et al., 2007b, Aflitto and DeGomez, 2015). Bomford and O'Brien (1990, p. 419) stated that sonic devises, other than those using alarm and distress calls, ‘have no persistent effect on animals’ space use or food intake’. Rats produce ultrasound alarm calls at ~22 kHz as part of their defence pattern against predators (Blanchard et al., 1991a, Litvin et al., 2007). ‘Lab’ rats have been shown to reduce activity after the playback of 22-kHz calls (Brudzynski and Chiu, 1995, Nicolas et al., 2007). Kim et al. (2010) found that 22-kHZ calls induced freezing in other rats but only if they had previously experienced an aversive event associated with a 2.9-kHZ sound. Endres et al. (2007) also showed that ‘Lab’ rats learned to associate 22-kHz calls with aversive stimuli. Artificially generated 20-kHz sounds were effective at inducing freezing in trials conducted by Beckett et al. (1997), Beckett et al. (1996).

Many sound-based animal repellents have been patented (e.g. Malleolo, 1997, Cauchy, 2001, Rich and Kneller, 2006), but there is little evidence of efficacy over long time frames of the repellent effects of ultrasound (Greaves and Rowe, 1969, Mason, 1998). Recent reviews have confirmed these views and do not refer to any new scientific validation of sound repellent for mammals (Aflitto and DeGomez, 2015). Smith and Meyer (2015) listed the limitations of the use of ultrasonic rodent devices, including the need for a power source, attenuation of signal, poor cost-effectiveness, lack of penetration of the signal, habituation and adverse effects on humans. A commercially available ultrasonic-wave emitter did not reduce the number of seabird nests predated by ship rats (Latorre et al., 2013). Zhelev et al. (2018) found no repellent effect on ship rats or Norway rats from an electronic device that combined ultrasonic waves, light signals and electromagnetic field change. Dormice (Eliomys melanurus) reduced movements and spent more time hiding when played calls of the tawny owl (Strix aluco) but spiny mice (Acomys cahirinus) did not, even though tawny owls are known to prey on the latter species (Hendrie et al., 1998). 39

Only one possum-specific acoustic repellent device has been assessed. Coleman & Tyson (1994, cited in Coleman et al., 2006) found that the ultrasonic ‘Po-guard’ did not prevent possums from entering pastures to forage. Coleman et al. (2006) noted the dearth of information on the effect of biologically meaningful acoustic signals on possum behaviour.

Acoustic devices appear to have some limited potential for carnivores. In one trial, although cats reduced exploration activity, they actually approached a commercial ultrasonic cat repellent and the only other behavioural change was increased ear flicking (Mills et al., 2000). However, an ultrasonic cat repellent did reduce entries of domestic cats into a garden and reduced the duration of these incursions (Nelson et al., 2006). Moreover, the aversion to the device increased over the weeks of deployment. Like most pest control devices, the positioning of the deterrent was thought to be an important determinant of its range. In a small-scale trial on captive animals, an ultrasonic device was shown to have no effect on food consumption by dingoes (Canis lupis) (Edgar et al., 2007).

Combining or alternating visual and acoustic signals might increase the repellent effects of these stimuli and reduce habituation (Baker et al., 2007b). Alternation between visual (clothing hung around the paddock) and auditory (man-made sounds and dog barking) repellents have shown efficacy in deterring large felid predator from attacking livestock in Mexico (Zarco‐González and Monroy‐Vilchis, 2014). Some marketed devices, such as Critter Gitter (https://cdn.shopify.com/s/files/1/0311/2753/files/Pestgard_Catalogue_2017.pdf), include a range of different loud, disruptive sounds as well as lights (Bell, 2008, Milanovich, 2010). However, their protective effects, if any, are limited to small areas (Shivik and Martin, 2000, Shivik et al., 2003, VerCauteren et al., 2005, Baker et al., 2007b) or work better with multiple device deployment (Linhart et al., 1992). Acoustic stimuli may have a role as salient cues for the establishment in aversive conditioning, i.e. if the sound is associated with a negative reinforcement (Smith et al., 2000, Götz and Janik, 2011).

For the use of sonic or ultrasonic devices, motion-activation can be a more effective deployment than random presentation as it reduces habituation. This has been demonstrated on wolves and 40 rats (Shivik and Martin, 2000, Fisol and Jubadi, 2010). Shivik (2006, p. 255) predicted that ‘more sophisticated sensor designs using radar and other technologies may result in sensors that are useful in a wide array of predation management situations’.

7.3 Mechanical repellents

Simple mechanical devices have advantages when used in the field in that they provide consistent repellent stimuli with little need for servicing. Barrier fences can be used to protect crops and wildlife sanctuaries (Hayward and Kerley, 2009, Smith and Meyer, 2015). There has been research conducted to determine effective designs to target feral cats, mustelids, rodents and possums in New Zealand (Clapperton and Matthews, 1996, Moseby and Read, 2006, Day and MacGibbon, 2007, Burns et al., 2012).

Mooring line and electrical cable shields are examples of simple devices to prevent rodents from invading ships and buildings. Various designs have been patented (e.g. Roberts, 1990, Hattenbach and Hahn, 1993). Some are augmented by sound and electric shock stimuli (Ratigan, 2015). Sheet metal and polycarbonate guards are also used to keep rats and possums off fruit trees and power poles (Pehling, 2012)( http://www.possumguard.com.au/; http://www.stuff.co.nz/marlborough-express/news/6969320/Great-lengths-to-foil-possums).

Systems that rely upon electricity have practical limitations for use in the field associated with power supply but modern solar systems may provide some solutions (Sharma et al., 2016). Electric training collars have worked to prevent predators from attacking livestock (Mason, 1998, Andelt et al., 1999, Breck et al., 2002), but were limited because of differences in responses among individuals as well as logistic, animal care and maintenance issues (Shivik et al., 2003).

There has been some success deterring rodents from gnawing on cables using mechanical/tactile stimuli. Abrasive substances like sand or glass can be added to paint (Fagerstone et al., 2012).

8. Combination repellents Single component repellents or cocktails? If animals combine cocktails of defensive compounds maybe we should too. Mason and Singer (2015) describe how animals use ‘acquired combinatorial chemical defence’ to defend against natural enemies and many insects use defence cocktails (Spiteller, 2008). Jones et al. (2016) also emphasised that natural and varied is better than simplistic unvaried synthetics, replicating a multi-predator environment to ensure the prey species is most likely to respond by leaving the area rather than just enhanced vigilance or ‘going to ground’. If synthetic repellents are to be developed, complexity could be important. While some chemical may be critical components for inducing specific behaviours, trials have shown that combinations of synthetic plant extracts are not always as effective as natural products (Ries et al., 2001). Efficacy may then depend both on the particular combination of compounds, other additives, and their sensory modality. Fischer et al. (2013a) found that a combination of black pepper oil, Chinese geranium and methyl nonyl ketone was no more repellent than black pepper oil alone to water voles, while Clayton (1988) patented a repellent for dogs and cats in which the addition of sodium di-C4-C13 alkylsulphosuccinate significantly enhanced the effect of red pepper or quinine.

One form of combination repellent is to use both primary- and secondary-acting compounds together. Mason et al. (2001) pointed out that primary repellents that act via irritation or fear can act as sensory cues for the establishment of CFA. This approach has been successfully used for bird repellents using d-pulegone and AQ (Clapperton et al., 2014, Clapperton et al., 2012, Day et al., 2012). Ballinger and Werner (2015) described a rodent repellent system that uses this combination of polycyclic quinone and irritant terpenes. They claim it is effective in preventing seed consumption by both ship rats and Norway rats. The combination of AQ and pennyroyal oil (major component being d-pulegone) was repellent to a New Zealand macroinvertebrate (Morgan et al., 2017). Another example is that while clove oil (containing eugenol) enhanced the repellent effect of ziram to European badgers (Meles meles) (Baker et al., 2008, Baker et al., 2005, Baker et al., 2007a). The addition of black pepper oil to the combination of methyl anthranilate and MNK increased repellency for mice (Hansen et al., 2016a).

Combination repellents can also include other sensory cues. Auditory visual, mechanical, and chemical stimuli can reinforce each other (Beauchamp, 1995). Munoz and Blumstein (2012) noted that species use multisensory stimuli in predator avoidance. There are rodent and predator repellent designs that use strobe light and/or ultrasonic sound and/or odour with a motion- detection device (e.g. Nichols, 2016, Waldman et al., 2017). Polycyclic quinones are particularly effective repellents for voles when paired with ultraviolet light (Werner et al., 2016). Rats can also see into the ultraviolet (Burn, 2008). Such multisensory approaches can produce longer lasting repellents than single-stimulus systems (Miller et al., 2016).

9. Conclusions There are a range of sources of chemicals that could be effective predator repellents for use in island/border protection, push-pull strategies for protection of specific sites, to re-direct hunting/foraging behaviour or even in mating disruption. They include chemicals that induce innate fear and/or anxiety responses, irritation, neophobia or malaise. Chemicals can also be used to condition learned food aversion or place avoidance to manage the behaviour of a stable predator population.

9.1 Predator odours

Predator odours are one source of repellent odours for rodents and much is known about the responses of rats and mice to cat and fox odours because they have been used as models for human anxiety research. Fur/body odours are likely to be most repellent as they indicate close proximity of the predator but may not be effective as broadcast repellents. To be used more effectively in wildlife management, much needs to be discovered about the active ingredients of fur odours (Hegab et al., 2015). The highly malodorous anal gland odours also have potential. The well-known fox urine component TMT could be assessed as a mustelid repellent. Likewise pyrazines, pyridines, butanoic acids from wolverine anal glands and PEA from large cat scents could be considered as components of repellents for all the New Zealand mammal pest species. Other potential animal-sourced of repellents include kairomones from mustelids, insects and amphibians, as well as rat alarm pheromones. Egg-based products are possible feeding deterrents. 43

Synthetic predator odour repellents should mimic as closely as possible the ‘real thing’. Apps et al. (2015) noted that terrestrial vertebrates use complex mixes of compounds for communication, not simple volatiles. The responses of prey depend upon the concentration, and age of the odours, and the diet of the predator producing the odour. If animals can show fear and aversion to odours that they have not previously encountered (Apfelbach et al., 2015a), this opens up an array of potential noxious compounds that could be included in repellency strategies in New Zealand. However, some odours may need to be pre-exposed to the animal during the critical period of odour sensitisation early in life, as demonstrated for mice and odours from cat urine (Voznessenskaya et al., 2016).

We must be aware of the context in which repellent effects are assessed. Laboratory-based trials might not be clear indicators of field efficacy (Voznessenskaya, 2014). Lima and Bednekoff (1999) predicted that experimental procedures that exposed prey to sudden intense odour signals would overestimate the efficacy of predator odours in the field, where prey are more likely to be constantly exposed to low levels of such odours and are living in their familiar home range. Nikaido and Nakashima (2009) showed that TMT-induced fear responses in ‘Lab’ rats were enhanced by environmental novelty.

It is important that responses to repellents do not rapidly habituate. Habituation has been demonstrated in the response of rodents to the odour of cats and ferrets (Dielenberg and McGregor, 1999, Weinberg et al., 2009, Hegab et al., 2014b). ‘Lab’ rats habituated to repeated exposure to ferret bedding odour (Weinberg et al., 2009). But earlier studies found few signs of habituation by rats to cat fur odour, and the response generalised to other novel odours (Zangrossi and File, 1992, Zangrossi and File, 1994).

While natural product and synthetic animal odour components have shown promise and methods to use them even patented (e.g. Weiser, 2005, Liberles and Ferrero, 2014), they have not become ‘magic bullet’ repellents. The absolute concentration of a repellent may not be as critical as for attractant lures (Jackson et al., 2016, Clapperton et al., 2017) — for repellents more is probably better — but the relative concentration of different components may be important, and effective 44 repellent concentrations can vary greatly amongst species (Forbey et al., 2013). There can also be seasonal variation in the responsiveness of prey to predator odours (Soltz-Herman and Valone, 2000).

We also need to understand the ecological framework to predict responses to predator odour- based lures (Jones et al., 2016). The complex web of ecological relationships might see small prey like mice and rats being attracted to rather than repelled from mustelid and cat odours so they can determine information on the relative abundance of the predator species and therefore predation threat (Jones et al., 2016). Synthetic repellents would need to replicate FRESH odour or they might act more as attractants rather than repellents. Even if the predator odours deter prey species, they could attract other predators of the same and other species (Clapperton et al., 2017). We also need more information on the potential of exposure to fear-inducing stimuli to reduce breeding success or induce demographic changes in prey populations.

Banks et al. (2014) noted that the risk-assessment response to predators is likely to be pulsed, with prey animals more responsive at times of high risk. Responses are also likely to be transient. Banks et al. (2016) explored the responses of not only prey but other predator species to olfactory signals of predators. Garvey et al. (2016) showed an example of this; stoats would approach and investigate the body scent of ferrets. This web of eavesdropping suggests that prey species would need to balance the benefit of approaching a predator odour cue not only against the risk of being caught by the scent leaver but also by other predators. Conversely, the potential for mesopredators to be repelled by apex predators is counterbalanced by the benefits they can gain from such interspecific eavesdropping behaviour. For example, as ferrets use chin-rubbing behaviour to scent mark caches of food (Wildhaber, 1984, Clapperton, 1985), this might partly explain the risky approach of stoats to ferret odour (Garvey et al., 2016).

Behavioural responses after the initial investigation of a predator odour will also be context specific (Hughes et al., 2010a, Jones et al., 2016). Food abundance and level of competition from other individuals and species may determine whether prey are prompted to either indulge in risk- taking activities or leave an area that contains high predator density (as indicated by abundant scent) (Jones et al., 2016, Dent et al., 2014). The vegetation cover can also play a role, with the 45 presence of potential bolt holes or dense cover providing an alternative strategy for predator avoidance (Merkens et al., 1991). The response of a prey to a predator odour will be affected by all these variables and their evolved suite of behavioural responses (Hegab et al., 2015). All these factors will, therefore, need to be considered when deploying odours as repellents.

Prey species already modify their behaviour to avoid predators — e.g. brushtail possums spend more time foraging in trees than on the ground where they are more likely to encounter predators so the addition of a predator odour (dog urine) to above-ground feeding stations produced little effect on foraging behaviour (Mella et al., 2014). Nor were the possums captured any less frequently in traps scented with fox, cat, quoll or dingo odour (Mella et al., 2010).

We have little understanding of how prey species distinguish between the odours of different individual predators but this has implications especially for the use of artificial animal-based repellents — the more natural and more varied they are, the more likely that the prey will believe that the area is inhabited by numerous predators.

9.2 Plant-based repellents

While the formulating of predator odours into usable products for widespread use in the field may be difficult and costly, plant-based compounds may be more producible — they are commonly used for other purposes and commercially available. PSMs have been studied as repellents for rodents and possums. There have been no studies on their effects on the behaviour of mustelids but domestic dog and cat repellents could point the direction towards repellents effective on other carnivores. Essential oils, terpenes and ketones from black pepper, geranium, eucalyptus, capsicum, cinnamon, fennel, pine needle and neem oils have all shown promise for various species. MNK, piperine, capsaicin, acetophenones, α- and β-pinene, pulegone and 8- cineole are among the active ingredients that that could be incorporated into synthetic repellent formulations. Polycyclic quinones are CFA-inducing agents and there are many other chemicals that have/are being assessed for this purpose. They can be combined with irritant primary repellents that can both enhance the repellent effect directly and act as salient cues for the CFA effect. It must be remembered that conditioned aversions are prone to habituation over time and new individuals would need to be conditioned if there is population turn-over. A range of other 46 chemicals have bitter flavours or are repellent in lower than lethal doses. These could be considered as ‘long shots’, worth further investigation.

9.3 Repellent identity and test procedures

New insect repellents and lures are being identified in a cost-effective manner using chemical molecule prospecting and modelling, bioassay procedures and even 3D-printed test mechanisms (Gupta and Bhattacharjee, 2007, Deletre et al., 2016b, Sullivan et al., 2017) but mammalian chemical and behavioural processes are more complex. Apps et al. (2015) found only small-scale patterns in form and function of mammalian semiochemicals. However, Jackson et al. (2016) recommended the use of integrated chemical image and response-guided approach for lure development, and structure-activity relationship studies are identifying new potential mammalian repellents (Osada et al., 2017).

We need species-specific test protocols that identify the appropriate behavioural responses of the target species. The responses of Norway rats to repellent stimuli have been well characterised but less work has been directed at ship rats. We cannot assume what works for one species will be appropriate for another (Jones and Dayan, 2000). We also need to determine response criteria for stoats. Erlinge (1977) listed retreat, fleeing, escape and whining/squealing vocalisations as submissive reactions when stoats meet each other. Behaviours observed during interactions between ferrets were described by Poole (1972), who differentiated and described deterrent defensive, aversive defensive and fearful defensive responses. Mustelids will respond to threat by release of anal sac odours (Clapperton, 1985, Gorman and Trowbridge, 1989). Possum defensive behaviour has not been clearly classified but Winter (1976) describes the responses of possums during agonistic interactions and Clapperton and Matthews (1996) described their ‘flight’ responses from electric shocks.

The need to establish the appropriate behavioural criteria is essential. Repellents can produce behavioural changes in predators but not necessarily ones that will protect the prey species of concern. For example, quinolizidine alkaloids reduced feeding but not hording of seeds by agouti Dasyprocta leporina (Guimarães et al., 2003). CFA is an effective means to reduce food consumption in some situations, but it does not always affect prey-killing behaviour (Burns and 47

Connolly, 1980, Mason et al., 2001). Ferrets modified their mouse-killing method from biting to using their feet when the mice were treated with aversive flavour and odour (Rusiniak et al., 1976). Predator odours sometimes elicit only physiological responses not behavioural ones. Perrot-Sinal et al. (1999) found that PTA caused concentrations of cortisone and adrenocorticotrophic hormone to increase in ‘Lab’ rats, with no associated change in locomotor activity.

9.4 Repellent commercialisation and application

To convert the success of repellents in the laboratory into cost-effective chemical repellents in the field, compatible delivery systems must be assessed. Developments in nanotechnology are producing slow-release systems for pesticides (Nuruzzaman et al., 2016). Hopefully this and other modern slow-release techniques might make it possible for repellent odours to be delivered into the environment with the necessary stability, solubility and permeability characteristics. They could be a way of delivering ‘FRESH’ predator odour, indicating the presence of a nearby predator.

Developing chemical repellents for mammals of conservation concern might always be limited by economic realities (Deletre et al., 2016b). This is especially true for stoats and possums. While rodents are universal pests that damage agricultural systems as well as wildlife, there is very limited demand for control systems for mustelids and marsupials.

We must be aware of the possibility of creating ‘dinner bells’ (Caretta & Barlow 2011 cited in Greggor et al., 2014). Mild irritants can become associated with the food source being protected, reinforcing approach and feeding rather than withdrawal. Mason et al. (2001) mentioned an unpublished result of moose (Alces alces) learning to associate wolf urine applied as a repellent with a salt source. This learned association behaviour might also explain the attractiveness of ultrasonic cat and badger ‘repellents’ (Mills et al., 2000, Ward et al., 2008).

Clark and Avery (2013) emphasised the value in integrating the use of chemical repellents with other management methods. Visual and auditory repellent systems have limited long-term effects on mammals but could be components of multisensory repellents. Mechanical devices might also 48 provide cost-effective solutions to some pest control situations. The closer we can get to producing the effect of a real predator by combining fresh odour with visual, auditory and movement cues, the more likely that we can manipulate the pest species’ movements, foraging and/or reproductive behaviour.

Smith and Meyer (2015, p. 105) noted that: ‘in practice, like all methods that do not exclude absolutely, behavioural manipulation is only effective if the animal can choose a more attractive alternative.’ Thus repellents must be seen as just the ‘push’ in a push-pull strategy aimed at increasing toxic bait consumption, entry into traps or movements away from birds’ nests or other areas, with the ‘pull’ being provided by other control systems. Suitable mixes of chemical repellents and multi-sensory systems could, however, play important roles in helping to protect our native fauna as we strive towards a predator-free New Zealand.

10. Acknowledgements I thank Maggie Nichols and Elaine Murphy for their help with obtaining the references. Tim Sjoberg, Tom Agnew and Elaine Murphy initiated this review, which was funded by ZIP.

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Table 1. Components of predator odours that have potential as rodent, mustelid or possum repellents. Odour source Species known to be References Compound Species Source repelled* o- Aminoacetophenone Mustelids Urine Ship rat, mouse (Mason et al., 1991a, Nolte et al., 1994a, Nolte et al., 1993) 2,5-Dihydro-2,4,5- Fox Faeces Norway rat, ship rat, (Burwash et al., 1998b, Fendt et al., 2005, Endres and trimethylthiazoline mouse Fendt, 2009, Fortes‐Marco et al., 2013) (TMT) 3,3-Dimethyl-1,2- Ferret, Anal gland Ship rat (Burwash et al., 1998b) dithiolane (DMDIT weasel Dimethyl pyrazines Ferret, wolf Urine Mouse, deer (Zhang et al., 2007, Osada et al., 2013, Osada et al., 2015, Osada et al., 2014, Osada et al., 2017, May, 2016) L-Felinine Cat Urine Mouse (Voznessenskaya et al., 2016) Hexanal Ferret, rat Body Norway rat (Inagaki et al., 2014, May, 2016) 2,4-Lutidine Mountain Urine Mouse (Brechbühl et al., 2015) lion 3-Mercapto-3- Felines Urine — (Apps et al., 2014) methylbutanol 3-Methyl-1-butanethiol Skunk Anal gland Mouse (Sievert and Laska, 2016) 2-Methylbutanoic acid Wolverine Anal gland — (Wood et al., 2005) 3-Methylbutanoic acid Wolverine Anal gland — (Wood et al., 2005) 2-Methylbutyric acid Ferret Body Norway(?) rat (May, 2016)

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2-Methyldecanoic acid Wolverine Anal gland — (Wood et al., 2005) 4-Methylpentanal Norway rat Perianal Norway rat (Inagaki et al., 2014) 2-Phenylethylamine Large felines Urine Norway rat, Mouse (Ferrero et al., 2011) (PEA) n-Propylthietane Ferret, stoat, Anal gland Norway rat, possum (Heale and Vanderwolf, 1994, Woolhouse and Morgan, (PTA) weasel 1995, Bramley et al., 2000) Pyridines Large felines Urine Mouse (Brechbühl et al., 2015, May, 2016) α-Tocopherol Wolverine Anal gland — (Wood et al., 2005) Trimethyl pyrazines Wolf Urine Mouse, deer (Osada et al., 2013, Osada et al., 2015, Osada et al., 2014, Osada et al., 2017) * A dash indicates that the component has not been scientifically tested on nay species

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Table 2. Plant secondary metabolites that have potential as rat, mustelid or possum repellents. Plant material Potential active components Species References repelled* Black pepper oil Piperine, acetophenones Ship rat (Nolte et al., 1993, Fagerstone et al., 2012, Fischer et al., 2013a, Hansen et al., 2015, Desoky et al., 2014) Bergamot oil Linalool, limonene, γ-terpinene Norway rat (Eleni et al., 2009, Kalandakanond-Thongsong et al., 2010, Kalandakanond-Thongsong et al., 2011) Capsicum Capsaicin — (Mason et al., 1991b, Shumake et al., 1999, Shumake et al., 2000, Jensen et al., 2003, Baylis et al., 2012, Numata and Willey, 2014) Cinnamon oil Cinnamamide, cinnamic aldehyde Norway rat (Crocker et al., 1993b, Spurr and Porter, 1998, Spurr et al., Ship rat 2001, Vijayan and Thampuran, 2004, Kaur, 2013, Babbar et al., 2015) Citronella Citronellal, geraniol Ship rat (Singla and Kaur, 2014, Saini, 2018) Daffodil extract β-sitosterol, tazettine, demethyl — (Ries et al., 2001) tazettine Eucalyptus oil 8-Cineole, α- and β-pinene, p- Ship rat, (Pass et al., 1998, Lawler et al., 1999, Marsh et al., 2003, cymene, eucamalol, limonene, brushtail Singla et al., 2013, Singla et al., 2014) linalool, γ-terpinene, α-terpineol, possum alloocimene aromadendrene, jensenone, macrocarpal G Fennel oil Not identified — (Hansen et al., 2015) 112

Geramium oil Citronellol, geraniol, citronellyl Norway rat (Kalandakanond-Thongsong et al., 2010, Kalandakanond- Thongsong et al., 2011, Sharopov et al., 2014) Mugwort oil Camphor, camphene, α-thujone, Rats (Sinha, 2014) germacrene D, 1,8-cineole, β- caryophyllene Neem oil Azadirachtin Norway rat (Gaoh, 1999); Singla & Parshad 2007 cited in (Singla et al., Ship rat 2014) Pine needle oil α- and β-Pinene, limonene — (Epple et al., 1996, Epple et al., 1995, Wager-Pagé et al., 1997) Rheum, Aloe, Polycyclic anthraquinones Norway rat (Ballinger and Werner, 2015, Clapperton et al., 2015, Cowan Rhannus, Cassia et al., 2015) Rue oil Methyl nonyl ketone (MNK; — (Fischer et al., 2013a, Fischer et al., 2013b, Hansen et al., undecanone-2) 2016a, Hansen et al., 2015, Hansen et al., 2016c) Szechuan Limonen, α-terpineol, linalool, Norway rat (Epple et al., 2001) pepper citral, citronellal, cineol dipentene, geraniol, alkylamides Wormwood oil Thujone — (Harding, 1987, Harding, 1989, Harding, 1988) * A dash indicates that the component has not been scientifically tested on Norway rats, ship rats or brushtail possums

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Table 3. Chemicals that have potential as conditioned food aversion agents for rodent, mustelids or possum repellents. Chemical Species repelled Prey protected References 9,10-Anthraquinone Brushtail possum, Experimental food (Clapperton et al., 2015, Cowan et al., 2015, Norway rats, ship Hansen et al., 2015, Werner et al., 2016) rats, other rodents, rabbits Antimony potassium tartrate Ferret Meat, eggs (Massei et al., 2003b, Norbury et al., 2005) Benzo[α]pyrene Norway rat Chocolate (Mahiout and Pohjanvirta, 2016) Caffeine Rats, brushtail Experimental foods (Cowan et al., 2016, White and Mason, 1985, possum Massei and Cowan, 2002) Carbachol Rat, mongoose, Eggs (Nicolaus et al., 1989b, Nicolaus and Nellis, birds 1987, Ferguson, 2016) Cinnamamide Norway rat Experimental food, pest (Crocker et al., 1993b, Spurr and Porter, 1998, control baits, natural food Spurr et al., 2001, Gill et al., 2000, Ngowo et al., 2003) Clotrimazole Norway rat Experimental food (Massei and Cowan, 2002) Ethinyl oestradiol Norway rats, Eggs, experimental food (Nicolaus et al., 1989a, Nicolaus et al., 1989c, ferret Gill et al., 2000, Norbury et al., 2005) Fluoxetine hydrochloride Norway rat Experimental food (Massei and Cowan, 2002) 6-Formylindolo(3,2- Norway rat Chocolate (Mahiout and Pohjanvirta, 2016) b)carbazole

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Levamisole Norway rat, Meat, eggs, experimental (Massei and Cowan, 2002, Massei et al., 2003a, ferret, fox food Massei et al., 2003b, Gentle et al., 2004) Lithium chloride Norway rat, Experimental food, sheep, (Nicolaus et al., 1989c, Burns and Connolly, brushtail possum, eggs 1980, Quick et al., 1985, Nachman and Ashe, coyote, fox, 1973, Burns, 1980, Clapperton et al., 1996) raccoon, skunk, opossum Methiocarb Rodents Natural food (Swihart, 1990, Reidinger, 1995) Methyl anthranilate and Norway rats, Water, experimental food (Nolte et al., 1994a, Hansen et al., 2015, Hansen dimethyl anthranilate mice, voles, birds et al., 2016c) β-Napthoflavone Norway rat Chocolate (Mahiout and Pohjanvirta, 2016) Sodium carbonate Fox Model eggs (Maguire et al., 2009) 2,3,7,8-Tetrachlorodibenzo Norway rat Chocolate, cheese (Tuomisto et al., 2000, Lensu et al., 2011) -p-dioxin Thiabendazole Norway rats, Eggs, experimental food (Massei and Cowan, 2002, Massei et al., 2003a, foxes Gill et al., 2000) Thiram Rodents, mice, Natural food (Nolte and Barnett, 2000, Cowan et al., 2016, brushtail possum Ngowo et al., 2003) Ziram Rodents, Natural food, experimental (Welch, 1967, Baker et al., 2007a) herbivores, food badgers

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