• By Ian Grettenberger, Luis Espino and Madi Hendrick •
Pyrethroids have been the go-to material of choice for tadpole shrimp management. Because they are widely used, there is a real concern that resistance to one or multiple active ingredients in this class (e.g., lambda cyhalothrin and zeta-cypermethrin).
As many of you may have heard, resistance appears to have cropped up in a few areas already, although it is fairly localized. Tadpole shrimp don’t move a lot across the landscape (lack of wings contributes to that!), so any resistance or “lack of susceptibility” issues likely will be localized to given fields or farms. We are conducting laboratory bioassays to measure resistance as part of our California Rice Research Board-funded research.
We were able to gather soil/eggs from some fields last year, although some samples didn’t produce any shrimp when we flooded up soil and some of this work was delayed with the changes with lab work due to COVID. Nevertheless, we noted some differences in susceptibility with the populations that we have assayed, with a roughly 25-fold difference in susceptibility between the most and least susceptible populations.
We use laboratory bioassays to expose shrimp to a range of lambda-cyhalothrin concentrations to determine how susceptible they are to this material (and likely most pyrethroids).
What we could use and if you are interested/able to help:
If you have fields that have tadpole shrimp and that we can gather some soil from, please let us know. We ideally will gather soil from fields before they are flooded but after they are prepped. If fields are untreated, we can also gather shrimp from the fields. Fields where resistance is suspected would great, but any fields work.
All we need is access and a place to go. Since sampling is straight-forward, we would just need a map or a map pin to go to. If you are interested, please email Ian and Madi at email@example.com and firstname.lastname@example.org. Madi Hendrick is the UCD graduate student that will be working on tadpole shrimp resistance. You can also call Ian at 530-752-0473 and he will return your call (likely not in the office).
Ian Grettenberger is a University of California Cooperative Extension specialist. Luis Espino is a UC Cooperative Extension rice systems advisor. Madi Hendrick is a UC Davis graduate student.