How much do you know about tadpole shrimp?

First, they're neither tadpoles nor shrimp. Second, they're  crustaceans and are pests of rice.  

Tadpole shrimp will be one of the topics that Cooperative Extension specialist Ian Grettenberger, an agricultural entomologist, will cover when the Bohart Museum of Entomology hosts a family friendly open house from 1 to 4 p.m., Saturday, May 28 in Room 1124 of the Academic Surge Building, Crocker Lane, UC Davis campus.

The event, free and open to the public, is themed “Bugs in Ag: What Is Eating Our Crops and What Is Eating Them?”  

Grettenberger, a member of the UC Davis Department of Entomology faculty, will discuss pests of rice and alfalfa and other agricultural crops, and also will cover such beneficial insects as lady beetles, aka lady bugs.

But back to tadpole shrimp.  We asked Grettenberger 10 facts that most people may not know about these critters. Here we go!

1. The common name for Triops species is tadpole shrimp because they look superficially like tadpoles (frogs), but another common name is shield shrimp, named after their shield-like carapace.
2. The genus name for tadpole shrimp, "Triops" comes from Latin "tri" (three) and Greek "?ps" (eye). They have two large compound eyes and a third simple eye (ocellus) used for detecting light.
3. The California crop where tadpole shrimp are relevant is rice. Triops longicaudatus is an early-season pest that can damage germinating seeds.
4. While the pest species Triops longicaudatus is an abundant species because it can do well in rice fields, another species in California, Lepidurus packardi (vernal pool tadpole shrimp), is endangered and relies on limited vernal pool habitats for survival.
5. Triops longicaudatus carry their eggs in egg sacs, where they are kept before being deposited.
6. Eggs of Triops longicaudatus typically dry out completely as rice fields are drained or pools dry. Eggs can survive for many years (10's of years) in a desiccated state, able to hatch when they are flooded again.
7. Triops longicaudatus are omnivorous, meaning they eat plant material, invertebrates, and even their siblings (cannibalism!).
8. Triops longicaudatus will eat mosquito larvae.
9. A possible sign of a rice field full of tadpole shrimp is very murky water; as they feed and burrow on the bottom, they stir up mud and muddy the water.
10. You can actually buy dried eggs of Triops longicaudatus and keep them as a pet.

Grettenberger plans to feature a few videos of the pests and their natural enemies and display live insects from alfalfa crops, as well as  tadpole shrimp. 

“We plan to talk broadly about the pests that eat our crops and the natural enemies that help protect them,” Grettenberger said. He and postdoctoral fellow Buddhi Achhami of the Grettenberger lab will field questions. (For more information on tadpole shrimp, be sure to access KQED's Deep Look video, Tadpole Shrimp Are Coming For Your Rice. which includes Grettenberger's expertise; and the UC Statewide Integrated Pest Management Program's information about tadpole shrimp.)

Also during the Bohart Museum open house, the family activity is to make tadpole shrimp hats or puppets. "Googly eyes" will be used to imitate the compound eyes and and the ocellus, said Tabatha Yang, the Bohart Museum education and outreach coordinator. 

The Bohart Museum, directed by Lynn Kimsey, UC Davis distinguished professor of entomology, houses a global collection of eight million insect specimens; a live "petting zoo" comprised of Madagascar hissing cockroaches, walking sticks (stick insects) and tarantulas; and a year-around gift shop (also online) stocked with insect-themed gifts, such as t-shirts, hooded sweatshirts, posters, jewelry, books, puppets, candy and collecting equipment. 

The Bohart Museum has been closed to the public for the last two years due to COVID-19 pandemic precautions. The Bohart observed UC Davis Picnic Day by setting up displays in the hallway of the Academic Surge Building. This spring the museum is open to the public, but groups must make reservations and everyone must follow the UC Davis visitor guidelines: https://campusready.ucdavis.edu/visitors? The museum's "visiting us" page includes more information.

Cooperative Extension agricultural specialist Ian Grettenberger of the UC Davis Department of Entomology and Nematology has received a research grant from the California Department of Pesticide Regulation (DPR) to study tadpole shrimp in rice.

Grettenberger's project, "Assessing a Biocontrol System for the Management of Tadpole Shrimp in Rice," is one of 10 research grants sharing $3.75 million meant to explore integrated pest management (IPM) tools for urban, non-agricultural and agricultural pest management, according to DPR Director Julie Henderson. 

The grant program,  funded by the state budget, represents a 617 percent increase from the previous year's funding. In the last decade, DPR has awarded $9,702,819 in research grants.

The grant projects "are critical to developing and expanding innovative practices and biological, non-chemical and physical tools to manage pests in agriculture, urban and other non-agricultural communities,” said Henderson. “The research will support the state's work to accelerate a systemwide transition to safer, more sustainable pest management and better protect human health and the environment.”

"Tadpole shrimp usefully eat some early season weeds but can cause damage to rice later in their life cycle," Grettenberger noted. "To preserve their role in controlling weeds but diminish the shrimp's later impact on the rice harvest, predator mosquito fish will be introduced mid-season to control the shrimp's population when necessary."

The 10 projects comprise two areas of research:

• Research projects funded for urban and agriculture pest management
• Research projects funded for urban and nonagricultural pest management

See projects funded.

Grettenberger, who joined the Department of Entomology and Nematology faculty in January 2019, received his bachelor of science degree in biology, with an ecology, evolution and organismal emphasis in 2009 from Western Washington University, Bellingham, Wash., and his doctorate in entomology in 2015 from Pennsylvania State University, State College, Pa. He served as a postdoctoral researcher in the Godfrey lab and later, in the Frank Zalom lab.

His fields of expertise include field and vegetable crops; integrated pest management; applied insect ecology, and biological control of pests. 

The California Department of Pesticide Regulation aims to protect human health and the environment "by fostering safer and sustainable pest management practices and operating a robust regulatory system to evaluate and register pesticides and monitor and regulate their sale and use across the state." (See more information about DPR.)

Rice growers currently rely heavily on pyrethroid insecticides  to manage tadpole shrimp, a crustacean pest that targets young rice seedlings in flooded rice fields. 

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.”

“In addition, we used large square metal plots to evaluate if a fish released for mosquito control, mosquitofish (Gambusia affinis), could suppress shrimp populations. We found that a number of materials could suppress shrimp populations, while unregistered materials did not provide sufficient control. Mosquitofish also proved able to suppress shrimp populations, although extremely high shrimp populations could escape predation and shrimp could outgrow risk to predators. These results could help a field crop industry move beyond pyrethroids, which will be important to address issues of environmental contamination or regulatory changes as well as changes in susceptibility.”

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, Joanna Bloese, and Kevin Goding)

Do you want to make sure your freshly planted rice fields don't look like the muddied mess on the left below (vs. clear on right) following a pyrethroid application? Wondering if your tadpole shrimp are becoming less susceptible to pyrethroids? We do too! Pyrethroids are widely used for managing resistance, and resistance seems to be a growing issue.

We are looking for additional fields where we can sample tadpole shrimp to test for pyrethroid resistance. We will be gathering soil/shrimp and then using these samples to run laboratory bioassays and measure susceptibility. The goal is to start measuring precisely how susceptible populations are in different fields. This will help us determine precisely how resistant known resistant populations are, how prevalent low levels of resistance are, and how “susceptible” currently susceptible populations are to generate baseline data. This will help generate the long-term baseline data we need to stay on top of this issue.

We will anonymize any publicly available data. In addition, we hope that by measuring resistance in individual fields, we can help you by noting any susceptibility slippage that may not have shown up yet in terms of control. We can also help address questions about whether lack of control is due to resistance or application issues.

Types of fields:

• Fields with known resistance to pyrethroids in tadpole shrimp (control issues).
• Suspect fields where you think resistance is an issue, but it is a just a hunch or a concern.
• Any other field. Even if pyrethroids have been working well, it is still good to know susceptibility levels and for us to generate baseline data.

What we need:

• Access to field(s)
• Summary of your ability to manage tadpole shrimp with pyrethroids, any declines in susceptibility, etc.

If you are interested, please email or call Ian Grettenberger at imgrettenberger@ucdavis.edu or (530) 752-0473.

This article was originally posted in the UC Rice Blog.