Insects and insecticides in agricultural landscapes: : socio-ecological challenges and patterns

Résumé

Pest management is essential to prevent crop losses. Chemical pesticides are standard practice in conventional farming systems because they are simple to use, cheap, and usually highly effective in providing short-term reduction in pest densities. Yet, their use can also lead to impacts on human health and biodiversity, pollution of air and water, and evolution of resistance in target pests. Chemical-based pest management can lead to lock-in because of an interplay of reinforcing environmental factors, science and technology, and socio-political factors, the so-called pesticide treadmill. To reduce farmers’ dependency upon pesticides and to lessen the associated environmental burden, a solid understanding of the socio-ecological features of pest management decision-making is needed. Using a multidisciplinary approach, I aimed to provide critically needed insight in the system dynamics underlying farmers’ pest control practices, and elucidate key principles governing a transition towards sustainable pest management.

First, I conducted a literature review to identify drivers of the pesticide treadmill. I found that pest management decisions at the farm level, characteristics of farming landscapes, science & technology, and societal demands are four domains with self-re-enforcing drivers for pesticide ‘lock-in’. Current pesticide use showed similarities with historical pesticide treadmills, as farmers remain trapped in the pesticide treadmill. An important difference is that I studied neonicotinoids at a global scale and in several crops, while documented historical examples of the pesticide treadmill were reported more locally and on a few cash crops. Second, in a two-year landscape study I assessed how beneficial arthropods and biocontrol services are jointly impacted by local and landscape-wide pesticide use and by semi-natural habitats in the landscape. I found that the abundance of beneficial arthropods was negatively associated with landscape-wide insecticide use, but biocontrol services in field margins were not significantly associated with insecticide use in the adjacent field or the wider landscape. Furthermore, landscapes with greater area of woody semi-natural habitat moderated insecticide use effects for parasitoids, but not for pollinators and arthropod predators. Third, I conducted an online survey among Dutch farmers to identify barriers towards reducing pesticide use. Farmers’ intention to reduce pesticide use was strongly determined by whether other farmers also acted, and farmers perceived limited capacity and autonomy to reduce pesticide use.

In this thesis I showed that current mainstream agriculture is trapped in a pesticide treadmill, which is reinforced by both a landscape and a social lock-in. Therefore, it is crucial that ecological information is integrated with social and behavioural understanding of pest management decision-making. Landscape management and increasing diversity is essential to facilitate beneficial insects. True costs of pesticide use and knowledge development on pest management alternatives could help farmers to overcome barriers to transition from chemical to ecologically-based pest management.