Overwintering Diapause and Survival of Western Leucotaraxis Argenticollis, a Promising Biological Control Agent for Adelges Tsugae, in the Eastern United States

Abstract

Successful use of biological control agents can be improved with a thorough understanding of the life history, survival, diapausing strategy, and synchrony with the host in the introduced range. Introduction of a novel organism can be influenced by abiotic factors that can impact the interactions with their target prey. Leucotaraxis argenticollis (Zetterstedt) and Le. piniperda (Malloch) (Diptera: Chamaemyiidae) are two species of predatory fly showing promise in the biological control program to manage the invasive hemlock woolly adelgid, Adelges tsugae, in eastern North America. Field releases of these Leucotaraxis spp. began in 2015, but little is known about their potential for survival or how they overwinter. In an effort to explore Le. argenticollis establishment potential, laboratory reared puparia were observed at seven sites, across a latitudinal gradient, on the east coast and one site on the west coast (native range) from July 20, 2020, to June 1, 2021. Adult Le. argenticollis emerged in spring 2021, after successfully overwintering as puparia, with a subset emerging in summer-fall 2020 at all observation sites. Results suggest that 1) the interaction of mean daily fall max temperatures and relative humidity has the most impact on survival, 2) mean daily minimum temperatures influence induction/maintenance of diapause, and 3) mean average daily temperatures and relative humidity impact survival to spring emergence. While this study supports continued research and release of Le. argenticollis, substantial variation in survival and facultative diapause was observed across a south to north gradient.

Keywords: biological control, diapause, A. tsugae, Leucotaraxis, Chamaemyiidae, Diptera