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The importance of plant richness to enhance the presence, biodiversity and efficiency of natural enemies in agricultural systems has largely been studied and demonstrated these last decades. Planting and preserving non-crop plants or manipulating crop richness in fields are practices that have proven their efficiency. However, the impact of crop-richness continuity in space and time on pests and natural enemies at a landscape scale remains poorly studied. In a two-year study, we assessed the effect of crop richness (single crop vs. multiple crops) on pest and natural enemy abundance and spillover in a field experiment in north-east China. Overall, we found crop diversity had a limited impact on pest and natural enemy abundance at the spatial scale tested (0.025 vs. 0.2 ha). The total pest and natural enemy abundances were not different between single-crop and multi-crop plots in either year, and the community composition at the functional group level was mostly determined by the crop but not crop diversity. However, we found that crop diversity influenced the numeric response of ladybirds to aphids in wheat; their negative response (higher abundance where aphid abundance was lower, suggesting predation) was attenuated in multi-crop plots (no correlation of aphid and ladybird abundance, suggesting the use of alternative resources). This pattern was not found in maize. Finally, crop succession enhanced the spillover of ladybirds from wheat and maize to cotton plots but with limited benefits for aphid control. Because of these limited impacts, we hypothesized that crop diversity may benefit natural enemy populations and enhance pest control at larger spatial scales; while we found similar abundances of ladybirds between our small (0.025–0.2 ha) plots and in large (2 ha) close-by cotton fields, aphid abundances were more than ten times higher in large cotton fields. Our study highlights the need to accurately estimate the spatial scale at which crop biodiversity may benefit pest control, in relation to the ecology of the target pest and natural enemies.

International audience; The South American tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is a serious worldwide threat to tomato industry. Since it has spread to the Afro-Eurasia, it was responsible of extensive damage and its control mainly relied on chemical insecticide applications. In this context, a survey of natural enemies attacking T absoluta spontaneously was conducted in Southern France. Infested tomato leaves were collected from protected tomato crops in seasons 2011 and 2012. Three species of mind predators [Macrolophus pygmaeus (Rambur), Nesidiocoris tenuis (Reuter) and Dicyphus sp.] were found preying on eggs and young larvae of the moth in both seasons of sampling. Eggs were also attacked by two trichogrammatid species, Trichogramma achaeae Nagaraja & Nagarkatti and Trichogramma sp. Whereas, T absoluta larvae were parasitized by four parasitoid species belong to the families; Braconidae (Bracon nigricans Szepligeti), Eulophidae [Neochrysocharis formosa (Westwood), Stenomesius sp. near japonicus and Necremnus sp. near artynes]. Although further studies are needed to assess the actual role of these species in T absoluta control, obtained results represent the first step towards developing biological and integrated management strategies against this pest in France. Furthermore, these results stress the need of conservation strategies of indigenous natural enemies to control the exotic pest species.

International audience; Seasonal population dynamics of Brevicoryne brassicae (L.) and Diaeretiella rapae (McIntosh) were studied in two canola (Brassica napus) fields with two different irrigation methods (flooding and sprinkler irrigations) from April to June 2010. Aphid and parasitoid (mummies) populations were sampled once a week. The highest aphid density was recorded on May 12th (792.5 +/- 55.5) and on May 18th (1701.1 +/- 195) in the sprinkler and flood irrigated fields, respectively. Parasitism rate recorded ranged from 0.4 to 19.5% and from 1.0 to 11.9% in sprinkler and flood irrigated fields, respectively. During the course of the study, there was no significant relationship between the weather values recorded and aphid populations observed in the field. However relationship with weather values was found in the case of D. rapae populations. Secondary parasitism was higher at the end of growing season and two hyperparasitoid species were dominant: Pachyneuron aphidis (Bouche) and Alloxysta fuscicomis (Ashmead). We discuss role of seasonal parasitism and irrigation systems for management of B. brassicae.

The capacity to assess invasion risk from potential crop pests before invasion of new regions globally would be invaluable, but this requires the ability to predict accurately their potential geographic range and relative abundance in novel areas. This may be unachievable using de facto standard correlative methods as shown for the South American tomato pinworm Tuta absoluta, a serious insect pest of tomato native to South America. Its global invasive potential was not identified until after rapid invasion of Europe, followed by Africa and parts of Asia where it has become a major food security problem on solanaceous crops. Early prospective assessment of its potential range is possible using physiologically based demographic modeling that would have identified knowledge gaps in T. absoluta biology at low temperatures. Physiologically based demographic models (PBDMs) realistically capture the weather-driven biology in a mechanistic way allowing evaluation of invasive risk in novel areas and climes including climate change. PBDMs explain the biological bases for the geographic distribution, are generally applicable to species of any taxa, are not limited to terrestrial ecosystems, and hence can be extended to support ecological risk modeling in aquatic ecosystems. PBDMs address a lack of unified general methods for assessing and managing invasive species that has limited invasion biology from becoming a more predictive science.