The effect of landscape context on the biological control of Sitobion avenae: temporal partitioning response of natural enemy guilds

Landscape contexts with high complexity may promote diversity of natural enemies, although the effect on biocontrol remains under discussion. Although biocontrol of Sitobion avenae is a well-studied system, little is known about the temporal effect of landscape context on the natural enemy assemblages. In a previous study, we showed a positive effect of predators in the decline of aphids; however, this effect had a temporal pattern responding to different landscape contexts. We study here two contrasting agricultural contexts, high landscape complexity with low intensification and low complexity with high intensification. Abundance and diversity of parasitoids was examined via a molecular approach, using a combination of diagnostic multiplex and singleplex PCR assays to test field-collected samples of S. avenae with genus- and species-specific parasitoid primer pairs. Temporal population dynamics were analyzed and differences related to these two contexts were observed. Parasitism rates were greater in the mid-sampling dates in high intensification simple landscapes, which were not observed for the low intensification complex landscapes. According to our results, we suggest that the greater landscape complexity in combination with a low agricultural intensification increase negative interactions for parasitoid population built-up; however, early predation by coccinellids was able to control the aphid populations. In contrast, under a simple landscape context with a high agricultural intensification, our results suggest an important role of parasitism with a complementary effect of late predation. We highlight the importance of different natural enemy guilds and their temporal dynamics under contrasting agricultural settings to further understand the relationship between functional diversity and biological control.