Alternative Chemical Control Options and Monitoring Techniques for Triops longicaudatus (Notostraca: Triopsidae) in California Rice

Abstract

The tadpole shrimp (Triops longicaudatus (Leconte); Notostraca; Triopsidae) is a vernal pool crustacean that has emerged as a significant pest for many rice farmers in California. Currently, lambda-cyhalothrin is the commercial standard and sole management practice for TPS, but resistance appears to be emerging. Field and laboratory trials were conducted from 2015 to 2018 at the Rice Experiment Station in Biggs, California, and in greenhouses at the University of California (UC) Davis to evaluate the efficacy of several alternative chemical controls and to explore early indicators of TPS activity and damage as monitoring tools. TPS mortality in plots treated with azadirachtin was not significantly different from those in the untreated control across all trials. Copper sulfate, lambda-cyhalothrin, and clothianidin were consistently effective across both lab and field trials. Chlorantraniliprole generated effective control in four of the five trials, whereas two diflubenzuron rates generated adequate control in the field, but not in laboratory bioassays. Thus, there appear to be several effective alternative control options available for farmers, should resistance to lambda-cyhalothrin continue to spread. Water turbidity (measured using a scale of 1-4) and the number of dislodged seedlings were both significantly correlated with TPS counts in field studies. Turbidity exhibited the highest correlations with TPS counts, suggesting that with further refinement it could play a valuable role in monitoring TPS populations.

Keywords: Triops longicaudatus; California rice; chemical management; tadpole shrimp; turbidity.