Mark Bolda, Santa Cruz, Monterey & San Benito UC County Farm Adviser, has reported on recent laboratory assays conducted in California demonstrating tolerance to Pyganic (pyrethrins), an organic insecticide used against spotted wing drosophila (SWD). The assays were conducted on a population that had been treated in the field with Pyganic many times.
Organic management tools for SWD are very limited. Entrust (spinosad) and Pyganic (pyrethrins) are the two most effective organic control methods, but both have short residual control times and must be applied frequently. This means that SWD are exposed to pesticides over multiple generations, which is a recipe for resistance development. The same situation exists with conventional insecticides, but there are more modes of action available to rotate, which lessens the likelihood of short term resistance development.
The two-year period from SWD detection to potential pesticide tolerance development is definitely short term and only highlights the fact that we need to manage SWD on a system-wide scale: optimizing non chemical/cultural management to reduce populations, wisely selecting pesticides, and rotating modes of action.
Suspected Tolerance to Pyganic (pyrethrin) Found in Spotted Wing Drosophila - Strawberries and Caneberries Blog