Control of Tadpole Shrimp 05

Control of Tadpole
Shrimp - 2005

Project Leader and Principal UC Investigators

Brian Tsukimura, associate professor, Dept. of Biology, CSU Fresno

Fresno state scientists continued work on an alternative to copper sulfate (bluestone) for treatment of tadpole shrimp. This invertebrate pest is of concern because it uproots young rice plants and reduces yield.

The compound under study is methyl farnesoate, an organic hormone that affects the reproductive organs of tadpole shrimp. The challenge has been to find a successful method of packaging the hormone into an effective delivery mechanism. Researchers have been experimenting with a pellet that works not unlike snail bait. The idea is to get the shrimp to ingest the hormone-laced bait and fail to reproduce. Objectives for 2005 work included:

Determine the most efficient mixing of ingredients into pellets
Test the efficacy of methyl farnesoate pellets in a rice field setting
Determine the capacity of tadpole shrimp to synthesize the hormone

"Researchers have been experimenting with a pellet that works not unlike snail bait. The idea is to get the shrimp to ingest the hormone-laced bait and fail to reproduce."

Previous experiments successfully demonstrated methyl farnesoate’s ability to disrupt tadpole shrimp reproduction. The compound was blended into a standard crustacean feed mixture—the bait. Problems were reported in this mixture, so scientists altered the recipe and have greatly improved the effectiveness of the treatment with a more stable mixture. The key was in understanding the best order to mix the ingredients, which included tadpole shrimp “food” like corn starch, gluten, lecithin, casein and cod liver oil.

The reformulated pellets were tested in a rice field to determine effective methyl farnesoate concentrations. Future research on application technology will examine timing and treatment levels relative to field inundation. Studies are also planned on the metabolic pathways tadpole shrimp utilize in degrading methyl farnesoate in order to assess its potential to develop resistance to the treatment.

The third area of research investigated the capacity of tadpole shrimp to synthesize methyl farnesoate. Using radioactive tracers, researchers observed the highest activity in the head or cephalic region, as well as ovaries and other reproductive organs.