Science for non-scientists (intro to my PhD thesis)

We live in a world where, despite producing enough food for everyone, the number of undernourished people went above 800 million in 2016 (FAO 2017). Since 2014, world hunger has been increasing every year. With projections estimating global population to reach 10 billion people by the year 2050, the challenge of food security needs to be tackled with extreme urgency.

Increasing food demand will inevitably put pressure to further intensify agricultural production, while sustainability goals (and common sense) require us to reduce negative environmental impacts as much as possible. Thus, a balance needs to be achieved, where ecosystem services can be exploited and food production secured, while still conserving biodiversity and minimizing detrimental effects to our environment.

Towards pesticide-free farming

In recent years, the spread of health and environmental concerns among Danish consumers has led to increases in sales and import of products grown organically.

By the end of 2015, 7% of all Danish farms were certified for organic production of primarily eggs, vegetables and dairy products (Danish Agriculture and Food Council 2015). Thus, the vast majority of farms still use conventional and/or intensive
production methods.

Conventional farms producing crops, fruits and vegetables, rely on various types of pesticides in order to combat weeds, insects and fungi. These chemicals can persist in the soil and migrate into groundwater systems, polluting our water supply and carrying the risk of dramatic non-target effects on other lifeforms. Contrarily, organic farming contributes to a variety of public goods in Denmark, with positive effects on, for example, biodiversity or human and animal health (Melby Jespersen et al. 2017).

The Danish Government is committed to limiting the use of pesticides as much as possible. In 2013, the pesticide tax was  changed so those products causing the highest pesticide loads, i.e. those that pose the highest risk, became more expensive
(Miljøministeriet 2013, Kudsk et al. 2018).

In April 2017, the new and ambitious Pesticide Strategy 2017-2021 was approved (Ministry of Environment and Food 2017), highlighting the importance of using alternative methods to combat unwanted weeds and pests.

In order to achieve the desired reductions in pesticide loads and to encourage conventional farmers to move into organic systems, it is of paramount importance that we develop and establish environmentally friendly methods for plant protection that serve as a desirable alternative to chemical pesticides, ultimately leading to a more sustainable food production.

Sustainable plant protection

Integrated Pest Management (IPM) involves the combination of different management approaches, like biological control, cultural practices or responsible use of pesticides. By synergistically combining different strategies, it aims at suppressing populations of agricultural pests while minimizing the risks to both consumers and the environment.

One of the pillars of IPM action is biological control: the use of beneficial organisms, i.e. natural enemies, to control pest populations. Biocontrol focuses primarily on (i) modifying the agricultural landscape to accommodate permanent populations of beneficial insects or (ii) releasing populations of natural enemies that can suppress pest outbreaks at specific points in time.

Beneficial insects were exploited already 1700 years ago, when farmers in ancient China used the weaver ant Oecophylla smaragdina to suppress pests in citrus orchards (Peng 1983). Today, that same ant is used for successful pest control in crops like pomelo, mango or cashew in Australia and South East Asia (Offenberg et al. 2013).

There are several reasons why ants have great potential as biocontrol agents. Ants are abundant and form large and stable populations that can use chemical recruitment to quickly react to increases in pest numbers (Way & Heong 2009).

Moreover, since ants are generalist predators, they can switch to another prey when a specific resource, e.g. pest species, becomes rare (Symondson et al. 2002). Even in scenarios where all prey is scarce, ants can survive periods of food shortage by cannibalizing their own brood (Sorensen et al. 1983, Rueppell & Kirkman 2005). These traits allow ant populations to persist in the environment when prey numbers are low, ensuring their presence in the system if and when pest populations start to reappear.

However, and despite this potential, ants can often exacerbate pest problems and become an obstacle for successful biological control.

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