Agroforestry has an impact on nocturnal predation by ground beetles and Opiliones in a temperate organic alley cropping system

The sustainability of organic vegetable cropping relies on ecosystem services such as biocontrol. Vegetable agroforestry can combine perennial woody crops and non-woody crops, which may alter ground predator activity-density and predation potential. We used living sentinel prey (Cydia pomonella) to assess predation in two different months, as a function of three levels of canopy openness in an agroforestry system combining lettuce crops and grassy strips. Ground beetles and arachnids were sampled throughout the year and we analyzed summer data conjointly to assess potential differences in the activity-density of these major predators between treatments. We found significantly higher predation potential in June in all agroforestry treatments compared to the control. In August, however, no differences were observed. Ground beetles and Opiliones were the major predators involved in observed predation events at both sampling periods. Differences in predation potential in June (- 35% in the control compared to agroforestry treatments) could be due to differences in Pterostichus madidus and Opiliones activity-density, which may have increased due to warmer temperatures under trees compared to the control plot.