Evaluation of Leucopis hennigrata (Diptera: Chamaemyiidae) as a classical biological control agent of Adelges nordmannianae (Hemiptera: Adelgidae) in northern Europe

•Leucopis hennigrata is a promising candidate for biological control of Adelges nordmannianae in Northern Europe.•L. hennigrata is a key predator of Ad. nordmannianae in Western Asia and Central Europe.•Under laboratory conditions larvae of L. hennigrata killed 57–117 eggs in 24 h.•Adult L. hennigrata oviposited on various non-target species, but rarely completed development.•Leucopis hennigrata was not found from non-target adelgids or aphids in the field.