The samples of DBM caterpillars were taken from brassica crops in Lincolnshire, Suffolk and Scotland.
Research leader Dr Steve Foster said: "Pyrethroids are normally the first choice of insecticides against moth pests but these tests indicate that resistance is present in the DBM population over a wide geographical spread."
He added: "If growers continue to use pyrethroids, this could be doubly damaging – not only would it not have an effect on DBM, it would be killing beneficial insects which attack DBM."
Foster will present his findings at an AHDB Horticulture workshop at PGRO near Peterborough on 24 January, which will provide the industry with an opportunity to discuss the implications of these on future pest management.
Pyrethroid resistance was first confirmed in one DBM sample from Lincolnshire in August. AHDB worked together with industry to produce an emergency 120-day authorisation for Benevia 10OD for use as an insecticide on a range of Brassica crops for DBM control.
"The Benevia approval meant growers had a product available that would work well alongside products containing spinosad as an active ingredient, but it does not currently have full label recommendation from the Chemical Regulation Directorate," Foster explained.