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Rice seedlings of different stages of development were infested with tadpole shrimp (TPS, Triops longicaudatus [LeConte]), of different sizes in four experiments conducted in a lath house in Colusa, CA, during 2015 and 2016. Tadpole shrimp size was based on carapace length. Rice seedling stages were classified as S0 if no structures were present; S1 if only the coleoptile was present; S2 if the coleoptile and radicle were present; S3-I if the prophyll had emerged; S3-II if the first true leave had emerged but was not unfurled; and V1 if the first true leave was unfurled. Results showed that TPS of all sizes are capable of injuring rice and reducing seedling establishment, with larger TPS causing more seedling establishment reduction than medium or small TPS. The coleoptile, radicle, and roots were the structures most injured by TPS. During the S0 stage, TPS buried seeds, preventing their establishment. Seedling stages S1, S2, and S3-I were found to have the highest risk of injury by TPS, while seedling stage V1 had the lowest. Pearson's correlation between injured seedlings and the normalized number of established seedlings indicates that injury to the coleoptile, root, and radicle combined are the most important in preventing seedling establishment. [ABSTRACT FROM AUTHOR]

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 forTPS, 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 ofTPS 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 monitoringTPS populations. [ABSTRACT FROM AUTHOR]

The tadpole shrimp [Triops longicaudatus (Leconte)] has emerged as a significant pest of rice grown in California in recent decades. The change in T. longicaudatus' pest status has coincided with changes in cultural management of residual rice straw postharvest. Policy changes have reduced the postharvest burning of fields from nearly 95% to less than 10%, promoting increased use of winter flooding as a means of accelerating straw decomposition. Field and laboratory trials were conducted from 2015 to 2017 at the Rice Experiment Station in Biggs, CA and in greenhouses at the University of California (UC) Davis to evaluate the effects of burning, flooding, and a fallow control on T. longicaudatus population dynamics. Experiments demonstrated that burning of rice straw failed to suppress densities of hatching T. longicaudatus and actually had the reverse effect, causing a 51% increase in numbers hatching, perhaps as a result of burning triggering termination of multiyear T. longicaudatus egg dormancy. Winter flooding had no measurable effect on T. longicaudatus hatch. Thus, these changes in winter cultural practices do not appear to be responsible for the emergence of T. longicaudatus as a major rice pest., (© The Author(s) 2020. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)