Agroforestry impacts the seasonal and diurnal activity of dominant predatory arthropods in organic vegetable crops

Abstract

Agroforestry can improve predator recruitment by increasing the diversity of microhabitats and modifying the microclimate. Four treatment plots were defined with three tree-shading levels in a 20 years old agroforestry system combining organic vegetable crops with hybrid walnut trees. Temperature and canopy openness were recorded in each treatment in July and September 2015 and arthropods were sampled using pitfall traps at two dates (2 weeks in July and 2 weeks in September). The daily activity pattern of the main taxa was then estimated using dry pitfall traps for 7 days in July and 8 days in September. Agroforestry significantly limited the daily temperature extremes in the day and night (± 1.5 °C). We observed a significant effect of treatment on species distribution. In July, the main xerophilic species, Pseudoophonus rufipes (Coleoptera, Carabidae), was less abundant in the two most shaded plots (− 25%). Pardosa hortensis (Arachnida, Lycosidae) showed significant differences in activity-density and diurnal activity between treatments. This spider was more active between 10:00 and 14:00 in the two most shaded treatments especially in tomatoes (more than 20% of the daily activity) compared to the control (13%). The activity-density of this species was also higher in the two shaded treatments than in the control (> 20%). Our results highlight that agroforestry, by buffering climate extremes, is likely to modify predatory arthropod activity and possibly the associated services such as biocontrol.