Importance of alternative predators of pear suckers (Cacopsylla pyri) in organic versus IPM pear orchards

Abstract: Pear suckers (Cacopsylla sp. or pear psylla) are widely considered to be the most important pest in pear orchards. Sustainable control of pear psylla relies on their natural suppression by beneficial arthropods and a well-tuned integration of crop protection treatments. Predatory bugs (Anthocoris sp.) are efficient predators of pear suckers, playing a crucial role in the control of pear psylla summer generations. However, their poor presence early and late in the season and their high mobility makes it difficult for growers to build up persistent predatory bug populations in their orchards to efficiently control pear psylla the whole season. Therefore, we investigated alternative natural enemies which potentially play an important role in the suppression of pear psylla, especially during early spring and autumn. To this end, a large-scale monitoring study was executed comprising extensive samplings throughout the year in fourteen pear orchards, and comparing psylla as well as beneficial fauna population developments between organic and IPM pear orchards. Organic orchards clearly displayed a lower pear psylla pressure correlating with higher proportions of specific predator populations, in particularly velvet mite (Trombidiidae) and spider (Araneae) populations. In addition, predation of C. pyri was verified by PCR-based gut content analysis. The outcome was analyzed in light of different treatment schedules, providing insights in potential side-effects of crop protection treatments on the composition of beneficial fauna in pear orchards.