Eupeodes americanus and Leucopis annulipes as potential biocontrol agents of the foxglove aphid at low temperatures

Description

Abstract: The foxglove aphid, Aulacorthum solani Kaltenbach (Hemiptera: Aphididae), has become a significant pest in ornamental horticulture as it can build high populations at low temperatures from 10-18 °C. Currently, only chemical control is used, as no commercially available biological control agent is effective at these temperatures. Two new potential biocontrol agents were evaluated in the laboratory at low temperatures: the silverfly, Leucopis annulipes Zetterstedt (Diptera: Chamaemyiidae) and the American hoverfly, Eupeodes (Metasyrphus) americanus (Wiedemann) (Diptera: Syrphidae). Active flight, oviposition and larval voracity were evaluated at 12 °C, 15 °C and 18 °C. The number of eggs laid by females was calculated after 7 days (18 °C, 15 °C, and 12 °C) and 14 days (12 °C). The number of aphids consumed by larvae was determined after 8 days and 8 hrs (12 °C), 6 days and 6 hrs (15 °C) and 5 days (18 °C). Results indicated that hoverflies laid a significantly higher number of eggs than silverflies at all temperatures. When given an additional 7 days at 12 °C, oviposition increased for both species. Hoverfly larvae consumed 2 times more aphids than silverfly larvae at 12 °C, 15 °C and 18 °C. Globally, the present study demonstrates a clear superiority of the hoverfly over the silverfly at low temperatures, and identifies it as a potential biocontrol agent of the foxglove aphid.