Comparative efficacy of three techniques for monitoring the establishment and spread of larval parasitoids recently introduced for biological control of emerald ash borer, Agrilus planipennis (Coleoptera: Buprestidae).
We compared three detection methods for two larval parasitoids introduced for the control of the emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae): Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae) and Spathius galinae Belokobylskij and Strazanac (Hymenoptera: Braconidae). The three methods compared were (1) debarking the lower 2 m of ash trees, (2) yellow pan traps (YPT), and (3) sentinel logs containing manually inserted late-instar EAB larvae. The parasitoids studied were released in a mixed hardwood forest in Cromwell, Connecticut from 2015 to 2017 and had established self-sustaining populations before this experiment. In 2019, we deployed all three detection methods along two transects (4.6 km and 5.7 km long, respectively) radiating out from the parasitoid release area. All three methods detected both parasitoid species. Each parasitoid was detected at the furthest transect point of at least one of the transects. Sentinel logs were the most efficient method for capturing T. planipennisi, with a labor requirement of 2.4 h/detection (139 h/57 broods). Debarking, in contrast, was the most efficient method for S. galinae, with a labor requirement of 3.6 h/detection (172 h/48 broods). YPT were the least efficient technique, capturing only 15 T. planipennisi and 9 S. galinae wasps for the entire trapping period at Cromwell, a labor requirement of 18.7 h/per detection (280 h/15 adults) and 31.1 h/detection (280 h/9 adults), respectively. We discuss the advantages and disadvantages of these three techniques.