Tage der Biodiversität 2027

Predatory mites (Acari: Phytoseiidae) are key natural enemies of pest mites and small insects in apple orchards. In Austria, apple cultivation comprises three main management systems: extensively managed meadow orchards („Streuobstwiesen“), organic orchards, and integrated orchards. Over two seasons, we sampled and identified predatory mites in southern Styria to compare their diversity across these three systems. We hypothesized that (1) mite diversity would be highest in extensive orchards due to the absence of pesticide applications, followed by organic orchards, and lowest in integrated orchards; and (2) tree canopies buffer thermal peaks, with this effect being significantly stronger in extensive orchards charcterized by taller trees.

Mites were collected monthly from leaves and subsequently identified. Additionally, ambient weather conditions were recorded using a mobile weather station, while leaf sensors monitored microclimate temperatures on the adaxial leaf surfaces in extensive and organic trees. Our diversity analyses (α- and β-diversity) partially supported our hypotheses: predatory mite diversity was notably higher in extensive orchards (18 species). However, diversity in organic and integrated orchards did not differ (8 species in both systems). As hypothesized, the canopy of extensively managed apple trees buffered daily peak temperatures up to 5°C more effectively than in organic trees.

We conclude that pesticide use is most likely the primary stressor reducing diversity in commercial orchards, in addition to considerably higher temperatures and potentially lower food resources. Ongoing climate change may exacerbate species decline in commercial orchards through direct heat stress and cumulative negative effects of heat stress and pesticides. Finally, our diversity analyses indicate that each extensive location hosts a distinct predatory mite community. This highlights the high conservation value of extensively managed meadow orchards, as they serve as vital reservoirs of climate-resilient natural enemies for commercial agriculture.