- Author: Kathy Keatley Garvey
Agricultural entomologist and Cooperative Extension specialist Ian Grettenberger of the UC Davis Department of Entomology and Nematology and his colleagues propose alternative management.
Grettenberger's poster, “Past Pyrethroids: Alternative Management Approaches for Tadpole Shrimp in Rice,” presented at Entomological Society of America meeting (Oct. 31-Nov. 3) in Denver, offers non-pesticide alternatives, including the use of mosquitofish.
Collaborative research with UCCE Butte County director and Rice Farming Systems Advisor Luis Espino and UC Davis staff research associate Kevin Goding, indicates that mosquitofish proved able to suppress shrimp populations.
“Tadpole shrimp (Triops longicaudatus) are an early-season pest in California rice,” Grettenberger explained in his abstract. “Soon after flooding, eggs hatch and growing shrimp are soon large enough to damage germinating rice seedlings. Currently, pyrethroid insecticides are heavily relied upon for management, as they are in many cropping systems, because of their efficacy and low cost. However, contamination of surface waters is a concern, as is insecticide resistance.”
"We evaluated alternative management strategies that could be used to manage tadpole shrimp,” he wrote. “We tested a number of materials using small metal ring plots and natural shrimp populations. This included several timings of applications to mimic an early, more proactive application along with a later, rescue application, as well as reduced rates of a number of insecticides.”
Deep Look Video. Tadpole shrimp recently made the national news in two ways, Grettenberger said. First, they made news with the sudden appearance of tadpole shrimp following monsoon rains this summer in an ancient ceremonial ball court at the Wupatki National Monument in northern Arizona (https://www.livescience.com/dinosaur-shrimp-emerge-arizona). In October, KQED's Deep Look released a new video, “Tadpole Shrimp Are Coming For Your Rice," the work of lead producer and cinematographer Josh Cassidy and other members of the Deep Look crew. (See https://youtu.be/T2xnXaX7r3g.) Grettenberger assisted with the project, providing tadpole shrimp and taking some of the video clips used in the five-minute video.
“Much of his shooting was in my garage,” the UC Davis entomologist said, “so I get to see just how much effort and care goes into producing these videos. They end up pretty short, but that doesn't mean it is simple to get all the pieces together.”
“This tadpole shrimp is coming for your rice,” the narrator said. “Hungry hordes of them find their way into the ice fields of California's Central Valley and go to town munching on the young seedlings. But where did they come from, with the ocean so far away? A couple of weeks ago, this was just a dry dusty field. Turns out they were here all along.”
Deep Look referred to them as “time travelers,” as the eggs of shrimp tadpoles can be viable for decades and hatch when the rice growers flood their fields. "At the very least, they have survived as eggs since last season," Grettenberger noted.
The pests are neither tadpoles or shrimp but are fresh-water crustaceans descended from the ocean. “They look like tiny horseshoe crabs,” Grettenberger told Deep Look. “It's obvious when rice fields have lots of tadpole shrimp in them, because they stir up the mud making the water look a bit like chocolate milk. There will also be shrimp zooming around, many upside down at the surface, popping up for a few seconds before disappearing back into the murkiness."
Adult tadpole shrimp cannot survive when the soil dries out. But Grettenberger said their eggs have a rugged outer layer called a “chorion” that protects the eggs from desiccation.
“They've been living this way for hundreds of millions of years-- since before the dinosaurs-- waiting out droughts, changing climates, even global catastrophes,” KQED relates in the video. “In a world where the future is unpredictable, tadpole shrimp are the ultimate survivors.”
Grettenberger, who joined the UC Davis Department of Entomology faculty in January, 2019, focuses his research on field and vegetable crops; integrated pest management; applied insect ecology; and biological control of pests.
Additional Information:
- Resource on tadpole shrimp, UC Statewide Integrated Pest Management Program (co-authors, the late Larry Godfrey, UC Davis Department of Entomology and Nematology; Luis Espino, UC Cooperative Extension; and Sharon Lawler, UC Davis Department of Entomology and Nematology
- "Effect of Rice Winter Cultural Management Practices on the Size of the Hatching Population of Triops longicaudatus (Notostraca:Triopsidae) in California Rice Fields" (Co-authors Larry Godfrey,
- Author: Kathy Keatley Garvey
Newly published research by a seven-member international team of scientists, including UC Davis agricultural entomologist Christian Nansen, points out the dilemma that rice farmers in Bangladesh and elsewhere in Asia are facing: Should we increase fertilizer inputs on our rice fields to maximize yields but then also increase the risk of a pest outbreak by the brown planthopper, Nilaparvata lugens? The planthopper is a major pest of rice in Asia, and it is resistant to many of the available insecticides.
Their research, “Higher Fertilizer Inputs Increase Fitness Traits of Brown Planthopper in Rice,” published July 5 in Scientific Reports of the journal Nature,” is online at http://rdcu.be/tWnE.
“This study underscores the importance of considering crop fertilization as a component of integrated pest management,” said Nansen, whose role included analyzing the data collected in Bangladesh and co-authoring the research paper. “That is, the management practices, including fertilizer regimes, impact the risk of pest outbreaks--just like the risk of humans falling ill is affected by our diet, the same applies to crop plants!”
In their research, conducted in Bangladesh, the scientists investigated the effects of three principal fertilizer components--nitrogen, phosphorus and potassium—on the development of potted rice plants and their effects on fitness traits of the brown planthopper.
“Compared to low fertilizer inputs, high fertilizer treatments induced plant growth but also favored brown planthopper development,” the scientists wrote in their abstraction. “The brown planthopper had higher survival, developed faster, and the intrinsic rate of natural increase was higher on well-fertilized than under-fertilized plants. Among the fertilizer inputs, nitrogen had the strongest effect on the fitness traits of brown planthopper.”
Rice, the primary food stable for more than half of the world's population, is cultivated in at least 114—mostly developing—countries. More than 100 million households in Asia and Africa derive their income from rice production. However, due to the growing population's increased demand for more rice, and limited land for production, yields must increase by at least 70 percent over the next three decades, Nansen said. “In many developing countries, increased use of fertilizers is a response to increase demand for rice.”
Nansen is an assistant professor with the UC Davis Department of Entomology and Entomology, and an affiliate of Bangladesh Rice Institute and the Zhejiang Academy of Agricultural Sciences, Hangzhou, China. He uses his international expertise to zero in on more sustainable farming systems, better food production and fewer pesticides.
Five members of the team are based at the Bangladesh Rice Institute in Gazipur, Bangladesh: M. P. Ali, M. M. Rashid, N. Ahmed, M. Jahan, and K. S. Islam. Co-author J. L. Willers is with the United States Department of Agriculture's Agricultural Research Service, Southern Insect Management Research Unit, Stoneville, Missouri.
Over the past decade, yield losses substantially decreased in Asia due to a widespread outbreak of the brown planthopper, the researchers said.1 For example, the Central Plains of Thailand sustained persistent planthopper outbreaks for 10 consecutive growing seasons from 2008 to 2012, with losses worth $52 million or equivalent to about 173,000 tons in 2010. The same pest was responsible for losses of around 1 million tons in Vietnam in 2007, and resulted in a government freeze on rice exports.
