Pre- and post-harvest protection strategies against

Since the beginning of farming from around 10,000 BC, people have developed methods to deter wildlife species and prevent crop damage (Larson et al. 2014). Children guarding the fields against birds, is one of the first methods of crop protection conveyed from the past (Conover 2002). In African and Asian countries, where subsistence farming requires low-cost measures which can be applied easily by the farmers themselves, various techniques to protect crops against wildlife species are in use to this day.

1.4.1. Barriers

Installations which aim at preventing species to enter crop fields, are frequently applied measures in African and Asian countries. Mostly, they were set up to keep out multiple species, not only wildlife but also free-ranging livestock. Plants with spines which hinder easy access by animals were planted systematically around fields, such as the common milk-hedge (Euphorbia neriifolia L.) to protect against deer or wild boars in India (Thapa 2010), or fast growing thorny trees and myrrhs (Commiphora spp. Jacq.) in Tanzania to protect against predators (Lichtenfeld et al. 2014). Bamboo fences have been erected to protect against wild and domestic herbivores in Asia, whilst the placement of thorny bushes around fields is used in semi-arid African countries. The digging of trenches to hinder elephants crossing has been used in Uganda (MacKenzie 2012) and India (Gubbi et al. 2014). Fences, electric or non-electric, have been installed around villages, around fields or along national parks (Hoare 2003). A disadvantage of all of these barrier systems was that they required high maintenance; the voltage of electric fences was reduced when high grasses were touching the

stances, trenches needed to be dug out after the rains and natural fences needed to be re-planted regularly.

1.4.2. Early warning systems

Early warning systems were used to warn farmers about approaching wildlife, such as trip-alarm techniques that produce noise when wildlife crosses (O'Connell-Rodwell et al. 2000), or watchtowers used for guarding. After being alerted, farmers would then start scaring wildlife with the aim of chasing it away from the fields. A modern type of early warning system has been developed in India, in areas where elephants use tea gardens as a refuge or need to move through them to reach de-connected forest patches. To decrease the likelihood of walking into a herd of elephants on the way home or to work, warning SMS were sent out to registered villagers to alert them about the presence of elephants on their way (Sugumar and Jayaparvathy 2013). Furthermore, well visible red LED lights were switched on at specific landmarks to warn villagers, in case of elephants’ presence in certain areas (Kumar and Raghhunathan 2014).

1.4.3. Frightening devices

Fear-provoking stimuli, which were used to increase animals’ fear of areas where crops were located, included visual, acoustic or olfactory techniques. Typical visual scaring devices included scarecrows or reflecting objects against birds (Marsh et al. 1991), reflective tape against deer or antelopes (Gilsdorf et al. 2002), or spotlights against elephants (Davies et al.

2011; Zimmermann et al. 2009). Acoustic deterrents included fire crackers or carbide-canons which were used against birds (Long 1981; Mott 1980) or elephants (Hedges and Gunaryadi 2009). In addition, alarm calls recorded and played back to wildlife species were used as acoustic deterrents; experiments to ward off Asian elephant bulls from food sources through the playback of vocalizations from a wild Asian elephant matriarchal group had resulted in flight responses by the bulls (Wijayagunawardane et al. 2016). One main constraint with the use of visual and acoustic deterrent techniques was the effect of habituation, where the noise or object had no biological relevance to the species. Such habituation to sounds has been shown for captive elephants with the playback sounds of buzzing by a disturbed beehive and the sound created by banging on pots and pans (Goodyear and Schulte 2015). Elephants were said to learn that the sound of blank cartridges had no direct effect on them and start ignoring it (Rachel McRobb 2014, personal communication), or birds stopped reacting to static raptor figures (Conover 2002). The combination of visual and acoustic techniques was, therefore,

recommended (Conover 2002). A promising combination of acoustic, visual and barrier techniques was the bee-hive fence against elephants (King et al. 2017). In this strategy, beehives were connected to a fence wire; once the elephants tried to break the fence, the beehives would move resulting in the alarmed bees starting buzzing and moving out of the hives, thus prompting the elephants to move away from the nuisance.

1.4.4. Olfactory repellents

Olfactory repellents are used against herbivores, by placing a repellent odour in crops and orchards to keep herbivores away. Extensive experiments have been conducted with small and medium sized herbivores and the odour of sympatric predators (faeces, urine, and fur) (Apfelbach et al. 2005; Sullivan et al. 1985). The repellent effect of predator odours was enhanced when the odour was applied on the plant needing protection, but was less effective in large crop fields. Other olfactory repellents which have been tested against African and Asian elephants were based on the extract from the fruit of the chilli plant (Capsicum spp. L.).; when sprayed against elephants, they were deterred from fields much faster than without the use of these repellents (Osborn 2002). This repellent effect of the chemical capsaicin, contained in the fruit of the chilli pepper, has been further used for other elephant repellents, such as chilli smoke produced by burning chilli briquettes, or chilli smokers made from dried chilli, tobacco leaves (Nicotiana tabacum L.), straw and cardboard (Osborn and Parker 2002; Zimmermann et al. 2009), or the application of a chilli-grease mixture on cotton cloth and sisal rope fences, so-called chilli fences (Karidozo and Osborn 2015).

The difficulty about all of these olfactory techniques is that the smell easily evaporates or washes off in the rain and, therefore, may not produce the expected results in field situations (Conover 2002; Sitati and Walpole 2006).

Besides the use as an olfactory repellent, chilli has been propagated as an alternative cash crop, as its fruits are not consumed by elephants and other herbivorous mammals (Parker and Osborn 2006). Other crops, containing high amounts of plant secondary metabolites (e.g.

medicinal and aromatic plants), may also be less attractive to wildlife herbivores. The cultivation of such crops has been initiated in several areas adjacent to national parks, especially in Nepal, India and Sri Lanka (Martin and Martin 2010; Santiapillai et al. 2010;

Thapa 2010; Tiller 2010). A profound knowledge on the repellent effects of crops containing plant secondary metabolites on the feeding behaviour of herbivores, did not exist before this study was conducted.