How to reinforce pollen beetle biocontrol at landscape level using a spatially explicit model?

Abstract: The intensification of agriculture has led to a loss of biodiversity, and subsequently a decrease in ecosystem services, such as natural regulation. Winter Oilseed Rape is an important oil crop in Europe and has to cope with numerous insects, which induce high pesticide use. Among the damaging insects, pollen beetle is the target of numerous pesticide utilizations, while natural regulation is known to induce high mortality rates. It appears that assessment of biological regulation of pests requires a landscape perspective (Bianchi et al., 2010) and modelling is now considered a powerful tool to infer mechanisms from spatial patterns (Vinatier et al., 2011b), and especially for tri-trophic interactions between plant, pest, and parasitoids. Therefore, we developed a lattice model called Mosaic-Pest to simulate the spatio-temporal dynamics of cohorts of pollen beetles and parasitoids in relation with landscape composition and structure. The model describes the most important processes (dispersal, mortality and fecundity) affecting population structure in space and time. Crop allocation in space and time, ploughing, and use of trap crops were explicitly considered in the model, on the basis of their influence on beetle and parasitoid populations. Species-specific parameters were derived from the literature available on the species or its closed taxon. Landscape mosaic and especially semi-natural habitats and oilseed rape crops were defined on the basis of GIS maps collected in north-western France, figuring contrasting situations in terms of landscape complexity. We tested various combinations of cultural practices affecting population of pollen beetles to select innovative integrated pest management strategies. The model showed a negative effect of trap crop on pollen beetle densities due to a diminution of pollen beetle egg-laying and an enhancement of parasitism. The model showed a relative low effect of ploughed soil tillage compared to other cultural practices but with a negative effect on pollen beetles infestations. Interaction between crop rotation and biological regulation was negative, because long crop rotation decreased the connectivity between fields, and consequently increased the mortality rate of both pollen beetles and parasitoids during dispersal events.