Evaluating detection methods for Trechnites insidiosus (Encyrtidae), a key natural enemy of pear psylla

Trechnites insidiosus (Encyrtidae) is the most common parasitoid of pear psylla, Cacopsylla pyri (Psyllidae). Parasitism rates vary wildly within and between orchards year-to-year but can reach as high as 80%. The cause of this variation remains unknown. In fact, surprisingly little is known about T. insidiosus and there are few published studies on Trechnites spp. more broadly. To understand T. insidosus we must first determine the best methods for monitoring. Four approaches were used to study T. insidosus abundance during the April-October 2019-2020 seasons: beat trays, sticky cards, screeded sticky cards, and 3D-printed tube traps. To study percent parasitism we sampled 10 leaves from 5 plots at 4 locations in Oregon and Washington. We screened leaves for immature pear psylla and then dissected each nymph for T. insidosus larvae and eggs. Further, these specimens were screened via PCR for T. insidosus DNA presence. Last, to monitor overwintering T. insidosus (pear psylla mummies) we placed small carboard bands on tree limbs prior to leaf drop in October and recovered the bands in February. We found both types of sticky cards performed better than beat trays and 3D-printed tube traps for T. insidosus detection. Screened sticky cards reduced bycatch while maintaining high levels of detection. The 3D-printed traps did not catch as many T. insidiosus but were much easier to process and preserved high quality DNA samples. Beat trays were the least effective monitoring tool. PCR outperformed dissection for T. insidosus detection. Cardboard bands were effective for collecting overwintering mummies.