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Landscape complexity may provide ecosystem services to agriculture through the provision of natural enemies of agricultural pests. Strong positive effect of adjacent semi-natural habitats on natural enemies in croplands has been evidenced, but the resulting impact on biological control remains unclear. Taking into account the temporal dynamics of pest and natural enemies in agricultural landscapes provides better resolution to the studies and better understanding of the biological control service. In this study, the population dynamics of aphids and two groups of predators (coccinellid and carabid beetles) were examined. Insects were sampled in 20 wheat fields, surrounded by structurally simple and complex landscapes in Chilean central valley. Considering the whole sampling period, the diversity of aphids and natural enemies were similar in wheat crops surrounded by both types of landscapes, and the abundance of ladybirds was higher in crops in the complex landscapes. The dynamics of predators was more advanced in complex landscapes than in the simple ones, whereas the dynamics of aphids were similar in both types of landscape. Negative correlation between abundance of predators and aphid population growth rate in both landscape contexts were observed suggesting a control of the pest population by the predators. Different temporal patterns were observed in these correlations in the two landscape contexts, which suggests differences in the biological control related to the landscape composition. The present study shows that colonization of crops by natural enemies occurs sooner in structurally complex landscapes and suggests that this early colonization may facilitate an early and efficient control of aphid populations, nevertheless the biological control efficiency seems to be higher in structurally simple landscapes later in the season.

Evidence is required to show that parasitoids are able to move between floral subsidies and the crop in sufficient numbers, and sufficiently rapidly to improve pest suppression. Marking and tracking techniques can elucidate parasitoid movement and the spatial structure of their population, and therefore, help determine the crop area in which to manage. This, in turn, would help in the deployment of nectar and pollen as resource subsidies, as well as determining the optimal timing for their implementation. Over two successive seasons, experiments were carried out to determine the effect of buckwheat (Fagopyrum esculentum) on the nutritional status and movement of the parasitoid Diadegma semiclausum and parasitism rates on its host Plutella xylostella. The number of parasitoids decreased significantly with the distance from the flowers; however, there was no trend in plots without flowers. The percentage of fed females varied from 72.4 to 77.7% irrespective of treatment. Although the results suggest that the parasitoids can move 80 m in a short period, parasitism rates were lower in a non-flower treated plot separated from a flower treated plot by just 60 m. Parasitoid mobility alone will not give a complete indication of the spatial arrangement to follow to produce enhanced parasitism rates. There is a clear difference between how far a parasitoid can move and how far apart floral subsidies should be deployed.